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Storage

OpenShift Container Platform 4.1

Configuring and managing storage in OpenShift Container Platform 4.1

Red Hat OpenShift Documentation Team

Abstract

This document provides instructions for configuring persistent volumes from various storage back ends and managing dynamic allocation from Pods.

Chapter 1. Understanding persistent storage

1.1. Persistent storage overview

Managing storage is a distinct problem from managing compute resources. OpenShift Container Platform uses the Kubernetes persistent volume (PV) framework to allow cluster administrators to provision persistent storage for a cluster. Developers can use persistent volume claims (PVCs) to request PV resources without having specific knowledge of the underlying storage infrastructure.

PVCs are specific to a project, and are created and used by developers as a means to use a PV. PV resources on their own are not scoped to any single project; they can be shared across the entire OpenShift Container Platform cluster and claimed from any project. After a PV is bound to a PVC, that PV can not then be bound to additional PVCs. This has the effect of scoping a bound PV to a single namespace, that of the binding project.

PVs are defined by a PersistentVolume API object, which represents a piece of existing, networked storage in the cluster that was provisioned by the cluster administrator. It is a resource in the cluster just like a node is a cluster resource. PVs are volume plug-ins like Volumes but have a lifecycle that is independent of any individual Pod that uses the PV. PV objects capture the details of the implementation of the storage, be that NFS, iSCSI, or a cloud-provider-specific storage system.

Important

High availability of storage in the infrastructure is left to the underlying storage provider.

PVCs are defined by a PersistentVolumeClaim API object, which represents a request for storage by a developer. It is similar to a Pod in that Pods consume node resources and PVCs consume PV resources. For example, Pods can request specific levels of resources, such as CPU and memory, while PVCs can request specific storage capacity and access modes. For example, they can be mounted once read-write or many times read-only.

1.2. Lifecycle of a volume and claim

PVs are resources in the cluster. PVCs are requests for those resources and also act as claim checks to the resource. The interaction between PVs and PVCs have the following lifecycle.

1.2.1. Provision storage

In response to requests from a developer defined in a PVC, a cluster administrator configures one or more dynamic provisioners that provision storage and a matching PV.

Alternatively, a cluster administrator can create a number of PVs in advance that carry the details of the real storage that is available for use. PVs exist in the API and are available for use.

1.2.2. Bind claims

When you create a PVC, you request a specific amount of storage, specify the required access mode, and create a storage class to describe and classify the storage. The control loop in the master watches for new PVCs and binds the new PVC to an appropriate PV. If an appropriate PV does not exist, a provisioner for the storage class creates one.

The PV volume might exceed your requested volume. This is especially true with manually provisioned PVs. To minimize the excess, OpenShift Container Platform binds to the smallest PV that matches all other criteria.

Claims remain unbound indefinitely if a matching volume does not exist or can not be created with any available provisioner servicing a storage class. Claims are bound as matching volumes become available. For example, a cluster with many manually provisioned 50Gi volumes would not match a PVC requesting 100Gi. The PVC can be bound when a 100Gi PV is added to the cluster.

1.2.3. Use Pods and claimed PVs

Pods use claims as volumes. The cluster inspects the claim to find the bound volume and mounts that volume for a Pod. For those volumes that support multiple access modes, you must specify which mode applies when you use the claim as a volume in a Pod.

Once you have a claim and that claim is bound, the bound PV belongs to you for as long as you need it. You can schedule Pods and access claimed PVs by including persistentVolumeClaim in the Pod’s volumes block.

1.2.4. PVC protection

PVC protection is enabled by default.

1.2.5. Release volumes

When you are finished with a volume, you can delete the PVC object from the API, which allows reclamation of the resource. The volume is considered released when the claim is deleted, but it is not yet available for another claim. The previous claimant’s data remains on the volume and must be handled according to policy.

1.2.6. Reclaim volumes

The reclaim policy of a PersistentVolume tells the cluster what to do with the volume after it is released. Volumes reclaim policy can either be Retain, Recycle, or Delete.

  • Retain reclaim policy allows manual reclamation of the resource for those volume plug-ins that support it.
  • Recycle reclaim policy recycles the volume back into the pool of unbound persistent volumes once it is released from its claim.
Important

The Recycle reclaim policy is deprecated in OpenShift Container Platform 4. Dynamic provisioning is recommended for equivalent and better functionality.

  • Delete reclaim policy deletes both the PersistentVolume object from OpenShift Container Platform and the associated storage asset in external infrastructure, such as AWS EBS or VMware vSphere.
Note

Dynamically provisioned volumes are always deleted.

1.3. Persistent volumes

Each PV contains a spec and status, which is the specification and status of the volume, for example:

PV object definition example

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv0001 1
spec:
  capacity:
    storage: 5Gi 2
  accessModes:
    - ReadWriteOnce 3
  persistentVolumeReclaimPolicy: Retain 4
  ...
status:
  ...

1
Name of the persistent volume.
2
The amount of storage available to the volume.
3
The access mode, defining the read-write and mount permissions.
4
The reclaim policy, indicating how the resource should be handled once it is released.

1.3.1. Types of PVs

OpenShift Container Platform supports the following PersistentVolume plug-ins:

  • AWS Elastic Block Store (EBS)
  • Fibre Channel
  • HostPath
  • iSCSI
  • NFS
  • VMWare vSphere

1.3.2. Capacity

Generally, a PV has a specific storage capacity. This is set by using the PV’s capacity attribute.

Currently, storage capacity is the only resource that can be set or requested. Future attributes may include IOPS, throughput, and so on.

1.3.3. Access modes

A PersistentVolume can be mounted on a host in any way supported by the resource provider. Providers have different capabilities and each PV’s access modes are set to the specific modes supported by that particular volume. For example, NFS can support multiple read-write clients, but a specific NFS PV might be exported on the server as read-only. Each PV gets its own set of access modes describing that specific PV’s capabilities.

Claims are matched to volumes with similar access modes. The only two matching criteria are access modes and size. A claim’s access modes represent a request. Therefore, you might be granted more, but never less. For example, if a claim requests RWO, but the only volume available is an NFS PV (RWO+ROX+RWX), the claim would then match NFS because it supports RWO.

Direct matches are always attempted first. The volume’s modes must match or contain more modes than you requested. The size must be greater than or equal to what is expected. If two types of volumes, such as NFS and iSCSI, have the same set of access modes, either of them can match a claim with those modes. There is no ordering between types of volumes and no way to choose one type over another.

All volumes with the same modes are grouped, and then sorted by size, smallest to largest. The binder gets the group with matching modes and iterates over each, in size order, until one size matches.

The following table lists the access modes:

Table 1.1. Access modes

Access ModeCLI abbreviationDescription

ReadWriteOnce

RWO

The volume can be mounted as read-write by a single node.

ReadOnlyMany

ROX

The volume can be mounted as read-only by many nodes.

ReadWriteMany

RWX

The volume can be mounted as read-write by many nodes.

Important

A volume’s AccessModes are descriptors of the volume’s capabilities. They are not enforced constraints. The storage provider is responsible for runtime errors resulting from invalid use of the resource.

For example, NFS offers ReadWriteOnce access mode. You must mark the claims as read-only if you want to use the volume’s ROX capability. Errors in the provider show up at runtime as mount errors.

iSCSI and Fibre Channel volumes do not currently have any fencing mechanisms. You must ensure the volumes are only used by one node at a time. In certain situations, such as draining a node, the volumes can be used simultaneously by two nodes. Before draining the node, first ensure the Pods that use these volumes are deleted.

Table 1.2. Supported access modes for PVs

Volume Plug-inReadWriteOnceReadOnlyManyReadWriteMany

AWS EBS

-

-

Fibre Channel

-

HostPath

-

-

iSCSI

-

NFS

VMWare vSphere

-

-

Note

Use a recreate deployment strategy for Pods that rely on AWS EBS.

1.3.4. Reclaim policy

The following table lists the current reclaim policy:

Table 1.3. Current reclaim policy

Reclaim policyDescription

Retain

Manual reclamation

Warning

If you do not want to retain all Pods, use dynamic provisioning.

1.3.5. Phase

Volumes can be found in one of the following phases:

Table 1.4. Volume phases

PhaseDescription

Available

A free resource not yet bound to a claim.

Bound

The volume is bound to a claim.

Released

The claim was deleted, but the resource is not yet reclaimed by the cluster.

Failed

The volume has failed its automatic reclamation.

The CLI shows the name of the PVC bound to the PV.

1.3.5.1. Mount options

You can specify mount options while mounting a PV by using the annotation volume.beta.kubernetes.io/mount-options.

For example:

Mount options example

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv0001
  annotations:
    volume.beta.kubernetes.io/mount-options: rw,nfsvers=4,noexec 1
spec:
  capacity:
    storage: 1Gi
  accessModes:
  - ReadWriteOnce
  nfs:
    path: /tmp
    server: 172.17.0.2
  persistentVolumeReclaimPolicy: Retain
  claimRef:
    name: claim1
    namespace: default

1
Specified mount options are used while mounting the PV to the disk.

The following PV types support mount options:

  • AWS Elastic Block Store (EBS)
  • iSCSI
  • NFS
  • VMWare vSphere
Note

Fibre Channel and HostPath PVs do not support mount options.

1.4. Persistent volume claims

Each persistent volume claim (PVC) contains a spec and status, which is the specification and status of the claim, for example:

PVC object definition example

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: myclaim 1
spec:
  accessModes:
    - ReadWriteOnce 2
  resources:
    requests:
      storage: 8Gi 3
  storageClassName: gold 4
status:
  ...

1
Name of the PVC
2
The access mode, defining the read-write and mount permissions
3
The amount of storage available to the PVC
4
Name of the StorageClass required by the claim

1.4.1. Storage classes

Claims can optionally request a specific storage class by specifying the storage class’s name in the storageClassName attribute. Only PVs of the requested class, ones with the same storageClassName as the PVC, can be bound to the PVC. The cluster administrator can configure dynamic provisioners to service one or more storage classes. The cluster administrator can create a PV on demand that matches the specifications in the PVC.

The cluster administrator can also set a default storage class for all PVCs. When a default storage class is configured, the PVC must explicitly ask for StorageClass or storageClassName annotations set to "" to be bound to a PV without a storage class.

1.4.2. Access modes

Claims use the same conventions as volumes when requesting storage with specific access modes.

1.4.3. Resources

Claims, such as Pods, can request specific quantities of a resource. In this case, the request is for storage. The same resource model applies to volumes and claims.

1.4.4. Claims as volumes

Pods access storage by using the claim as a volume. Claims must exist in the same namespace as the Pod by using the claim. The cluster finds the claim in the Pod’s namespace and uses it to get the PersistentVolume backing the claim. The volume is mounted to the host and into the Pod, for example:

Mount volume to the host and into the Pod example

kind: Pod
apiVersion: v1
metadata:
  name: mypod
spec:
  containers:
    - name: myfrontend
      image: dockerfile/nginx
      volumeMounts:
      - mountPath: "/var/www/html" 1
        name: mypd 2
  volumes:
    - name: mypd
      persistentVolumeClaim:
        claimName: myclaim 3

1
Path to mount the volume inside the Pod
2
Name of the volume to mount
3
Name of the PVC, that exists in the same namespace, to use

1.5. Block volume support

You can statically provision raw block volumes by including API fields in your PV and PVC specifications.

The following table displays which volume plug-ins support block volumes.

Table 1.5. Block volume support

Volume Plug-inManually provisionedDynamically provisioned

AWS EBS

Fibre Channel

 

HostPath

  

iSCSI

 

NFS

  

VMWare vSphere

Important

Block volume support is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see https://access.redhat.com/support/offerings/techpreview/.

1.5.1. Block volume examples

PV example

apiVersion: v1
kind: PersistentVolume
metadata:
  name: block-pv
spec:
  capacity:
    storage: 10Gi
  accessModes:
    - ReadWriteOnce
  volumeMode: Block 1
  persistentVolumeReclaimPolicy: Retain
  fc:
    targetWWNs: ["50060e801049cfd1"]
    lun: 0
    readOnly: false

1
volumeMode field indicating that this PV is a raw block volume.

PVC example

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: block-pvc
spec:
  accessModes:
    - ReadWriteOnce
  volumeMode: Block 1
  resources:
    requests:
      storage: 10Gi

1
volumeMode field indicating that a raw block PVC is requested.

Pod specification example

apiVersion: v1
kind: Pod
metadata:
  name: pod-with-block-volume
spec:
  containers:
    - name: fc-container
      image: fedora:26
      command: ["/bin/sh", "-c"]
      args: [ "tail -f /dev/null" ]
      volumeDevices:  1
        - name: data
          devicePath: /dev/xvda 2
  volumes:
    - name: data
      persistentVolumeClaim:
        claimName: block-pvc 3

1
volumeDevices, similar to volumeMounts, is used for block devices and can only be used with PersistentVolumeClaim sources.
2
devicePath, similar to mountPath, represents the path to the physical device.
3
The volume source must be of type persistentVolumeClaim and must match the name of the PVC as expected.

Table 1.6. Accepted values for VolumeMode

ValueDefault

Filesystem

Yes

Block

No

Table 1.7. Binding scenarios for block volumes

PV VolumeModePVC VolumeModeBinding Result

Filesystem

Filesystem

Bind

Unspecified

Unspecified

Bind

Filesystem

Unspecified

Bind

Unspecified

Filesystem

Bind

Block

Block

Bind

Unspecified

Block

No Bind

Block

Unspecified

No Bind

Filesystem

Block

No Bind

Block

Filesystem

No Bind

Important

Unspecified values result in the default value of Filesystem.

Chapter 2. Configuring persistent storage

2.1. Persistent Storage Using AWS Elastic Block Store

OpenShift Container Platform supports AWS Elastic Block Store volumes (EBS). You can provision your OpenShift Container Platform cluster with persistent storage using AWS EC2. Some familiarity with Kubernetes and AWS is assumed.

The Kubernetes persistent volume framework allows administrators to provision a cluster with persistent storage and gives users a way to request those resources without having any knowledge of the underlying infrastructure. AWS Elastic Block Store volumes can be provisioned dynamically. Persistent volumes are not bound to a single project or namespace; they can be shared across the OpenShift Container Platform cluster. Persistent volume claims are specific to a project or namespace and can be requested by users.

Important

High-availability of storage in the infrastructure is left to the underlying storage provider.

Additional References

2.1.1. Creating the EBS Storage Class

StorageClasses are used to differentiate and delineate storage levels and usages. By defining a storage class, users can obtain dynamically provisioned persistent volumes.

Procedure

  1. In the OpenShift Container Platform console, click StorageStorage Classes.
  2. In the storage class overview, click Create Storage Class.
  3. Define the desired options on the page that appears.

    1. Enter a name to reference the storage class.
    2. Enter an optional description.
    3. Select the reclaim policy.
    4. Select kubernetes.io/aws-ebs from the drop down list.
    5. Enter additional parameters for the storage class as desired.
  4. Click Create to create the storage class.

2.1.2. Creating the Persistent Volume Claim

Prerequisites

Storage must exist in the underlying infrastructure before it can be mounted as a volume in OpenShift Container Platform.

Procedure

  1. In the OpenShift Container Platform console, click StoragePersistent Volume Claims.
  2. In the persistent volume claims overview, click Create Persistent Volume Claim.
  3. Define the desired options on the page that appears.

    1. Select the storage class created previously from the drop-down menu.
    2. Enter a unique name for the storage claim.
    3. Select the access mode. This determines the read and write access for the created storage claim.
    4. Define the size of the storage claim.
  4. Click Create to create the persistent volume claim and generate a persistent volume.

2.1.3. Volume Format

Before OpenShift Container Platform mounts the volume and passes it to a container, it checks that it contains a file system as specified by the fsType parameter in the persistent volume definition. If the device is not formatted with the file system, all data from the device is erased and the device is automatically formatted with the given file system.

This allows using unformatted AWS volumes as persistent volumes, because OpenShift Container Platform formats them before the first use.

2.1.4. Maximum Number of EBS Volumes on a Node

By default, OpenShift Container Platform supports a maximum of 39 EBS volumes attached to one node. This limit is consistent with the AWS volume limits.

OpenShift Container Platform can be configured to have a higher limit by setting the environment variable KUBE_MAX_PD_VOLS. However, AWS requires a particular naming scheme (AWS Device Naming) for attached devices, which only supports a maximum of 52 volumes. This limits the number of volumes that can be attached to a node via OpenShift Container Platform to 52.

2.2. Persistent storage using NFS

OpenShift Container Platform clusters can be provisioned with persistent storage using NFS. Persistent volumes (PVs) and persistent volume claims (PVCs) provide a convenient method for sharing a volume across a project. While the NFS-specific information contained in a PV definition could also be defined directly in a Pod definition, doing so does not create the volume as a distinct cluster resource, making the volume more susceptible to conflicts.

Additional resources

2.2.1. Provisioning

Storage must exist in the underlying infrastructure before it can be mounted as a volume in OpenShift Container Platform. To provision NFS volumes, a list of NFS servers and export paths are all that is required.

Procedure

  1. Create an object definition for the PV:

    apiVersion: v1
    kind: PersistentVolume
    metadata:
      name: pv0001 1
    spec:
      capacity:
        storage: 5Gi 2
      accessModes:
      - ReadWriteOnce 3
      nfs: 4
        path: /tmp 5
        server: 172.17.0.2 6
      persistentVolumeReclaimPolicy: Retain 7
    1
    The name of the volume. This is the PV identity in various oc <command> pod commands.
    2
    The amount of storage allocated to this volume.
    3
    Though this appears to be related to controlling access to the volume, it is actually used similarly to labels and used to match a PVC to a PV. Currently, no access rules are enforced based on the accessModes.
    4
    The volume type being used, in this case the nfs plug-in.
    5
    The path that is exported by the NFS server.
    6
    The host name or IP address of the NFS server.
    7
    The reclaim policy for the PV. This defines what happens to a volume when released.
    Note

    Each NFS volume must be mountable by all schedulable nodes in the cluster.

  2. Verify that the PV was created:

    $ oc get pv
    NAME     LABELS    CAPACITY     ACCESSMODES   STATUS      CLAIM  REASON    AGE
    pv0001   <none>    5368709120   RWO           Available                    31s
  3. Create a persistent volume claim which binds to the new PV:

    apiVersion: v1
    kind: PersistentVolumeClaim
    metadata:
      name: nfs-claim1
    spec:
      accessModes:
        - ReadWriteOnce 1
      resources:
        requests:
          storage: 5Gi 2
    1
    As mentioned above for PVs, the accessModes do not enforce security, but rather act as labels to match a PV to a PVC.
    2
    This claim looks for PVs offering 1Gi or greater capacity.
  4. Verify that the persistent volume claim was created:

    $ oc get pvc
    NAME         STATUS   VOLUME   CAPACITY   ACCESS MODES   STORAGECLASS   AGE
    nfs-claim1   Bound    pv0001   4Gi        RWO            gp2            2m

2.2.2. Enforcing disk quotas

You can use disk partitions to enforce disk quotas and size constraints. Each partition can be its own export. Each export is one PV. OpenShift Container Platform enforces unique names for PVs, but the uniqueness of the NFS volume’s server and path is up to the administrator.

Enforcing quotas in this way allows the developer to request persistent storage by a specific amount, such as 10Gi, and be matched with a corresponding volume of equal or greater capacity.

2.2.3. NFS volume security

This section covers NFS volume security, including matching permissions and SELinux considerations. The user is expected to understand the basics of POSIX permissions, process UIDs, supplemental groups, and SELinux.

Developers request NFS storage by referencing either a PVC by name or the NFS volume plug-in directly in the volumes section of their Pod definition.

The /etc/exports file on the NFS server contains the accessible NFS directories. The target NFS directory has POSIX owner and group IDs. The OpenShift Container Platform NFS plug-in mounts the container’s NFS directory with the same POSIX ownership and permissions found on the exported NFS directory. However, the container is not run with its effective UID equal to the owner of the NFS mount, which is the desired behavior.

As an example, if the target NFS directory appears on the NFS server as:

$ ls -lZ /opt/nfs -d
drwxrws---. nfsnobody 5555 unconfined_u:object_r:usr_t:s0   /opt/nfs

$ id nfsnobody
uid=65534(nfsnobody) gid=65534(nfsnobody) groups=65534(nfsnobody)

Then the container must match SELinux labels, and either run with a UID of 65534, the nfsnobody owner, or with 5555 in its supplemental groups in order to access the directory.

Note

The owner ID of 65534 is used as an example. Even though NFS’s root_squash maps root, uid 0, to nfsnobody, uid 65534, NFS exports can have arbitrary owner IDs. Owner 65534 is not required for NFS exports.

2.2.3.1. Group IDs

The recommended way to handle NFS access, assuming it is not an option to change permissions on the NFS export, is to use supplemental groups. Supplemental groups in OpenShift Container Platform are used for shared storage, of which NFS is an example. In contrast block storage, such as iSCSI, use the fsGroup SCC strategy and the fsGroup value in the Pod’s securityContext.

Note

It is generally preferable to use supplemental group IDs to gain access to persistent storage versus using user IDs.

Because the group ID on the example target NFS directory is 5555, the Pod can define that group ID using supplementalGroups under the Pod’s securityContext definition. For example:

spec:
  containers:
    - name:
    ...
  securityContext: 1
    supplementalGroups: [5555] 2
1
securityContext must be defined at the Pod level, not under a specific container.
2
An array of GIDs defined for the Pod. In this case, there is one element in the array. Additional GIDs would be comma-separated.

Assuming there are no custom SCCs that might satisfy the Pod’s requirements, the Pod likely matches the restricted SCC. This SCC has the supplementalGroups strategy set to RunAsAny, meaning that any supplied group ID is accepted without range checking.

As a result, the above Pod passes admissions and is launched. However, if group ID range checking is desired, a custom SCC is the preferred solution. A custom SCC can be created such that minimum and maximum group IDs are defined, group ID range checking is enforced, and a group ID of 5555 is allowed.

Note

To use a custom SCC, you must first add it to the appropriate service account. For example, use the default service account in the given project unless another has been specified on the Pod specification.

2.2.3.2. User IDs

User IDs can be defined in the container image or in the Pod definition.

Note

It is generally preferable to use supplemental group IDs to gain access to persistent storage versus using user IDs.

In the example target NFS directory shown above, the container needs its UID set to 65534, ignoring group IDs for the moment, so the following can be added to the Pod definition:

spec:
  containers: 1
  - name:
  ...
    securityContext:
      runAsUser: 65534 2
1
Pods contain a securityContext specific to each container and a Pod’s securityContext which applies to all containers defined in the Pod.
2
65534 is the nfsnobody user.

Assuming the default project and the restricted SCC, the Pod’s requested user ID of 65534 is not allowed, and therefore the Pod fails. The Pod fails for the following reasons:

  • It requests 65534 as its user ID.
  • All SCCs available to the Pod are examined to see which SCC allows a user ID of 65534. While all policies of the SCCs are checked, the focus here is on user ID.
  • Because all available SCCs use MustRunAsRange for their runAsUser strategy, UID range checking is required.
  • 65534 is not included in the SCC or project’s user ID range.

It is generally considered a good practice not to modify the predefined SCCs. The preferred way to fix this situation is to create a custom SCC A custom SCC can be created such that minimum and maximum user IDs are defined, UID range checking is still enforced, and the UID of 65534 is allowed.

Note

To use a custom SCC, you must first add it to the appropriate service account. For example, use the default service account in the given project unless another has been specified on the Pod specification.

2.2.3.3. SELinux

By default, SELinux does not allow writing from a Pod to a remote NFS server. The NFS volume mounts correctly, but is read-only.

To enable writing to a remote NFS server, follow the below procedure.

Prerequisites

  • The container-selinux package must be installed. This package provides the virt_use_nfs SELinux boolean.

Procedure

  • Enable the virt_use_nfs boolean using the following command. The -P option makes this boolean persistent across reboots.

    # setsebool -P virt_use_nfs 1

2.2.3.4. Export settings

In order to enable arbitrary container users to read and write the volume, each exported volume on the NFS server should conform to the following conditions:

  • Every export must be exported using the following format:

    /<example_fs> *(rw,root_squash)
  • The firewall must be configured to allow traffic to the mount point.

    • For NFSv4, configure the default port 2049 (nfs) and port 111 (portmapper).

      NFSv4

      # iptables -I INPUT 1 -p tcp --dport 2049 -j ACCEPT
      # iptables -I INPUT 1 -p tcp --dport 111 -j ACCEPT

    • For NFSv3, there are three ports to configure: 2049 (nfs), 20048 (mountd), and 111 (portmapper).

      NFSv3

      # iptables -I INPUT 1 -p tcp --dport 2049 -j ACCEPT
      # iptables -I INPUT 1 -p tcp --dport 20048 -j ACCEPT
      # iptables -I INPUT 1 -p tcp --dport 111 -j ACCEPT

  • The NFS export and directory must be set up so that they are accessible by the target Pods. Either set the export to be owned by the container’s primary UID, or supply the Pod group access using supplementalGroups, as shown in group IDs above.

2.2.4. Reclaiming resources

NFS implements the OpenShift Container Platform Recyclable plug-in interface. Automatic processes handle reclamation tasks based on policies set on each persistent volume.

By default, PVs are set to Retain.

Once claim to a PVC is deleted, and the PV is released, the PV object should not be reused. Instead, a new PV should be created with the same basic volume details as the original.

For example, the administrator creates a PV named nfs1:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: nfs1
spec:
  capacity:
    storage: 1Mi
  accessModes:
    - ReadWriteMany
  nfs:
    server: 192.168.1.1
    path: "/"

The user creates PVC1, which binds to nfs1. The user then deletes PVC1, releasing claim to nfs1. This results in nfs1 being Released. If the administrator wants to make the same NFS share available, they should create a new PV with the same NFS server details, but a different PV name:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: nfs2
spec:
  capacity:
    storage: 1Mi
  accessModes:
    - ReadWriteMany
  nfs:
    server: 192.168.1.1
    path: "/"

Deleting the original PV and re-creating it with the same name is discouraged. Attempting to manually change the status of a PV from Released to Available causes errors and potential data loss.

2.2.5. Additional configuration and troubleshooting

Depending on what version of NFS is being used and how it is configured, there may be additional configuration steps needed for proper export and security mapping. The following are some that may apply:

NFSv4 mount incorrectly shows all files with ownership of nobody:nobody

  • Could be attributed to the ID mapping settings, found in /etc/idmapd.conf on your NFS.
  • See this Red Hat Solution.

Disabling ID mapping on NFSv4

  • On both the NFS client and server, run:

    # echo 'Y' > /sys/module/nfsd/parameters/nfs4_disable_idmapping

2.3. Persistent Storage Using iSCSI

You can provision your OpenShift Container Platform cluster with persistent storage using iSCSI. Some familiarity with Kubernetes and iSCSI is assumed.

The Kubernetes persistent volume framework allows administrators to provision a cluster with persistent storage and gives users a way to request those resources without having any knowledge of the underlying infrastructure.

Important

High-availability of storage in the infrastructure is left to the underlying storage provider.

Important

When you use iSCSI on Amazon Web Services, you must update the default security policy to include TCP traffic between nodes on the iSCSI ports. By default, they are ports 860 and 3260.

2.3.1. Provisioning

Verify that the storage exists in the underlying infrastructure before mounting it as a volume in OpenShift Container Platform. All that is required for the iSCSI is the iSCSI target portal, a valid iSCSI Qualified Name (IQN), a valid LUN number, the filesystem type, and the PersistentVolume API.

Optionally, you can provide multipath portals and the Challenge Handshake Authentication Protocol (CHAP) configuration.

Example 2.1. Persistent Volume Object Definition

apiVersion: v1
kind: PersistentVolume
metadata:
  name: iscsi-pv
spec:
  capacity:
    storage: 1Gi
  accessModes:
    - ReadWriteOnce
  iscsi:
     targetPortal: 10.16.154.81:3260
     portals: ['10.16.154.82:3260', '10.16.154.83:3260']
     iqn: iqn.2014-12.example.server:storage.target00
     lun: 0
     fsType: 'ext4'
     readOnly: false
     chapAuthDiscovery: true
     chapAuthSession: true
     secretRef:
       name: chap-secret

2.3.2. Enforcing Disk Quotas

Use LUN partitions to enforce disk quotas and size constraints. Each LUN is one persistent volume. Kubernetes enforces unique names for persistent volumes.

Enforcing quotas in this way allows the end user to request persistent storage by a specific amount (e.g, 10Gi) and be matched with a corresponding volume of equal or greater capacity.

2.3.3. iSCSI Volume Security

Users request storage with a PersistentVolumeClaim. This claim only lives in the user’s namespace and can only be referenced by a pod within that same namespace. Any attempt to access a persistent volume claim across a namespace causes the pod to fail.

Each iSCSI LUN must be accessible by all nodes in the cluster.

2.3.4. iSCSI Multipathing

For iSCSI-based storage, you can configure multiple paths by using the same IQN for more than one target portal IP address. Multipathing ensures access to the persistent volume when one or more of the components in a path fail.

To specify multi-paths in the pod specification use the portals field. For example:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: iscsi_pv
spec:
  capacity:
    storage: 1Gi
  accessModes:
    - ReadWriteOnce
  iscsi:
    targetPortal: 10.0.0.1:3260
    portals: ['10.0.2.16:3260', '10.0.2.17:3260', '10.0.2.18:3260'] 1
    iqn: iqn.2016-04.test.com:storage.target00
    lun: 0
    fsType: ext4
    readOnly: false
1
Add additional target portals using the portals field.

2.3.5. iSCSI Custom Initiator IQN

Configure the custom initiator iSCSI Qualified Name (IQN) if the iSCSI targets are restricted to certain IQNs, but the nodes that the iSCSI PVs are attached to are not guaranteed to have these IQNs.

To specify a custom initiator IQN, use initiatorName field.

apiVersion: v1
kind: PersistentVolume
metadata:
  name: iscsi_pv
spec:
  capacity:
    storage: 1Gi
  accessModes:
    - ReadWriteOnce
  iscsi:
    targetPortal: 10.0.0.1:3260
    portals: ['10.0.2.16:3260', '10.0.2.17:3260', '10.0.2.18:3260']
    iqn: iqn.2016-04.test.com:storage.target00
    lun: 0
    initiatorName: iqn.2016-04.test.com:custom.iqn 1
    fsType: ext4
    readOnly: false
1
Specify the name of the initiator.

2.4. Persistent storage using the Container Storage Interface (CSI)

The Container Storage Interface (CSI) allows OpenShift Container Platform to consume storage from storage backends that implement the CSI interface as persistent storage.

Important

Container Storage Interface is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see https://access.redhat.com/support/offerings/techpreview/.

Note

OpenShift Container Platform does not ship with any CSI drivers. It is recommended to use the CSI drivers provided by community or storage vendors.

OpenShift Container Platform 4.1 supports version 1.0.0 of the CSI specification.

2.4.1. CSI Architecture

CSI drivers are typically shipped as container images. These containers are not aware of OpenShift Container Platform where they run. To use CSI-compatible storage backend in OpenShift Container Platform, the cluster administrator must deploy several components that serve as a bridge between OpenShift Container Platform and the storage driver.

The following diagram provides a high-level overview about the components running in pods in the OpenShift Container Platform cluster.

Architecture of CSI components

It is possible to run multiple CSI drivers for different storage backends. Each driver needs its own external controllers' deployment and DaemonSet with the driver and CSI registrar.

2.4.1.1. External CSI controllers

External CSI Controllers is a deployment that deploys one or more pods with three containers:

  • An external CSI attacher container translates attach and detach calls from OpenShift Container Platform to respective ControllerPublish and ControllerUnpublish calls to the CSI driver.
  • An external CSI provisioner container that translates provision and delete calls from OpenShift Container Platform to respective CreateVolume and DeleteVolume calls to the CSI driver.
  • A CSI driver container

The CSI attacher and CSI provisioner containers communicate with the CSI driver container using UNIX Domain Sockets, ensuring that no CSI communication leaves the pod. The CSI driver is not accessible from outside of the pod.

Note

attach, detach, provision, and delete operations typically require the CSI driver to use credentials to the storage backend. Run the CSI controller pods on infrastructure nodes so the credentials are never leaked to user processes, even in the event of a catastrophic security breach on a compute node.

Note

The external attacher must also run for CSI drivers that do not support third-party attach or detach operations. The external attacher will not issue any ControllerPublish or ControllerUnpublish operations to the CSI driver. However, it still must run to implement the necessary OpenShift Container Platform attachment API.

2.4.1.2. CSI Driver DaemonSet

The CSI driver DaemonSet runs a pod on every node that allows OpenShift Container Platform to mount storage provided by the CSI driver to the node and use it in user workloads (pods) as persistent volumes (PVs). The pod with the CSI driver installed contains the following containers:

  • A CSI driver registrar, which registers the CSI driver into the openshift-node service running on the node. The openshift-node process running on the node then directly connects with the CSI driver using the UNIX Domain Socket available on the node.
  • A CSI driver.

The CSI driver deployed on the node should have as few credentials to the storage backend as possible. OpenShift Container Platform will only use the node plug-in set of CSI calls such as NodePublish/NodeUnpublish and NodeStage/NodeUnstage, if these calls are implemented.

2.4.2. Example CSI deployment

Since OpenShift Container Platform does not ship with any CSI driver installed, this example shows how to deploy a community driver for OpenStack Cinder in OpenShift Container Platform.

Procedure

  1. Create a new project where the CSI components will run, and then create a new service account to run the components. An explicit node selector is used to run the Daemonset with the CSI driver also on master nodes.

    # oc adm new-project csi --node-selector=""
    Created project csi
    
    # oc create serviceaccount cinder-csi
    serviceaccount "cinder-csi" created
    
    # oc adm policy add-scc-to-user privileged system:serviceaccount:csi:cinder-csi
    securitycontextconstraints.security.openshift.io/privileged added to: ["system:serviceaccount:csi:cinder-csi"]
  2. Apply this YAML file to create the deployment with the external CSI attacher and provisioner and DaemonSet with the CSI driver.

    # This YAML file contains all API objects that are necessary to run Cinder CSI
    # driver.
    #
    # In production, this needs to be in separate files, e.g. service account and
    # role and role binding needs to be created once.
    #
    # It serves as an example how to use external attacher and external provisioner
    # images shipped with {product-title} with a community CSI driver.
    
    kind: ClusterRole
    apiVersion: rbac.authorization.k8s.io/v1
    metadata:
      name: cinder-csi-role
    rules:
      - apiGroups: [""]
        resources: ["persistentvolumes"]
        verbs: ["create", "delete", "get", "list", "watch", "update", "patch"]
      - apiGroups: [""]
        resources: ["events"]
        verbs: ["create", "get", "list", "watch", "update", "patch"]
      - apiGroups: [""]
        resources: ["persistentvolumeclaims"]
        verbs: ["get", "list", "watch", "update", "patch"]
      - apiGroups: [""]
        resources: ["nodes"]
        verbs: ["get", "list", "watch", "update", "patch"]
      - apiGroups: ["storage.k8s.io"]
        resources: ["storageclasses"]
        verbs: ["get", "list", "watch"]
      - apiGroups: ["storage.k8s.io"]
        resources: ["volumeattachments"]
        verbs: ["get", "list", "watch", "update", "patch"]
      - apiGroups: [""]
        resources: ["configmaps"]
        verbs: ["get", "list", "watch", "create", "update", "patch"]
    
    ---
    
    kind: ClusterRoleBinding
    apiVersion: rbac.authorization.k8s.io/v1
    metadata:
      name: cinder-csi-role
    subjects:
      - kind: ServiceAccount
        name: cinder-csi
        namespace: csi
    roleRef:
      kind: ClusterRole
      name: cinder-csi-role
      apiGroup: rbac.authorization.k8s.io
    
    ---
    apiVersion: v1
    data:
      cloud.conf: W0dsb2JhbF0KYXV0aC11cmwgPSBodHRwczovL2V4YW1wbGUuY29tOjEzMDAwL3YyLjAvCnVzZXJuYW1lID0gYWxhZGRpbgpwYXNzd29yZCA9IG9wZW5zZXNhbWUKdGVuYW50LWlkID0gZTBmYTg1YjZhMDY0NDM5NTlkMmQzYjQ5NzE3NGJlZDYKcmVnaW9uID0gcmVnaW9uT25lCg== 1
    kind: Secret
    metadata:
      creationTimestamp: null
      name: cloudconfig
    ---
    kind: Deployment
    apiVersion: apps/v1
    metadata:
      name: cinder-csi-controller
    spec:
      replicas: 2
      selector:
        matchLabels:
          app: cinder-csi-controllers
      template:
        metadata:
          labels:
            app: cinder-csi-controllers
        spec:
          serviceAccount: cinder-csi
          containers:
            - name: csi-attacher
              image: quay.io/k8scsi/csi-attacher:v1.0.0
              args:
                - "--v=5"
                - "--csi-address=$(ADDRESS)"
                - "--leader-election"
                - "--leader-election-namespace=$(MY_NAMESPACE)"
                - "--leader-election-identity=$(MY_NAME)"
              env:
                - name: MY_NAME
                  valueFrom:
                    fieldRef:
                      fieldPath: metadata.name
                - name: MY_NAMESPACE
                  valueFrom:
                    fieldRef:
                      fieldPath: metadata.namespace
                - name: ADDRESS
                  value: /csi/csi.sock
              volumeMounts:
                - name: socket-dir
                  mountPath: /csi
            - name: csi-provisioner
              image: quay.io/k8scsi/csi-provisioner:v1.0.0
              args:
                - "--v=5"
                - "--provisioner=csi-cinderplugin"
                - "--csi-address=$(ADDRESS)"
              env:
                - name: ADDRESS
                  value: /csi/csi.sock
              volumeMounts:
                - name: socket-dir
                  mountPath: /csi
            - name: cinder-driver
              image: k8scloudprovider/cinder-csi-plugin:v0.3.0
              command: [ "/bin/cinder-csi-plugin" ]
              args:
                - "--nodeid=$(NODEID)"
                - "--endpoint=unix://$(ADDRESS)"
                - "--cloud-config=/etc/cloudconfig/cloud.conf"
              env:
                - name: NODEID
                  valueFrom:
                    fieldRef:
                      fieldPath: spec.nodeName
                - name: ADDRESS
                  value: /csi/csi.sock
              volumeMounts:
                - name: socket-dir
                  mountPath: /csi
                - name: cloudconfig
                  mountPath: /etc/cloudconfig
          volumes:
            - name: socket-dir
              emptyDir:
            - name: cloudconfig
              secret:
                secretName: cloudconfig
    
    ---
    
    kind: DaemonSet
    apiVersion: apps/v1
    metadata:
      name: cinder-csi-ds
    spec:
      selector:
        matchLabels:
          app: cinder-csi-driver
      template:
        metadata:
          labels:
            app: cinder-csi-driver
        spec:
          2
          serviceAccount: cinder-csi
          containers:
            - name: csi-driver-registrar
              image: quay.io/k8scsi/csi-node-driver-registrar:v1.0.2
              securityContext:
                privileged: true
              args:
                - "--v=5"
                - "--csi-address=$(ADDRESS)"
              env:
                - name: ADDRESS
                  value: /csi/csi.sock
                - name: KUBE_NODE_NAME
                  valueFrom:
                    fieldRef:
                      fieldPath: spec.nodeName
              volumeMounts:
                - name: socket-dir
                  mountPath: /csi
            - name: cinder-driver
              securityContext:
                privileged: true
                capabilities:
                  add: ["SYS_ADMIN"]
                allowPrivilegeEscalation: true
              image: k8scloudprovider/cinder-csi-plugin:v0.3.0
              command: [ "/bin/cinder-csi-plugin" ]
              args:
                - "--nodeid=$(NODEID)"
                - "--endpoint=unix://$(ADDRESS)"
                - "--cloud-config=/etc/cloudconfig/cloud.conf"
              env:
                - name: NODEID
                  valueFrom:
                    fieldRef:
                      fieldPath: spec.nodeName
                - name: ADDRESS
                  value: /csi/csi.sock
              volumeMounts:
                - name: socket-dir
                  mountPath: /csi
                - name: cloudconfig
                  mountPath: /etc/cloudconfig
                - name: mountpoint-dir
                  mountPath: /var/lib/origin/openshift.local.volumes/pods/
                  mountPropagation: "Bidirectional"
                - name: cloud-metadata
                  mountPath: /var/lib/cloud/data/
                - name: dev
                  mountPath: /dev
          volumes:
            - name: cloud-metadata
              hostPath:
                path: /var/lib/cloud/data/
            - name: socket-dir
              hostPath:
                path: /var/lib/kubelet/plugins/csi-cinderplugin
                type: DirectoryOrCreate
            - name: mountpoint-dir
              hostPath:
                path: /var/lib/origin/openshift.local.volumes/pods/
                type: Directory
            - name: cloudconfig
              secret:
                secretName: cloudconfig
            - name: dev
              hostPath:
                path: /dev
    1
    Replace with cloud.conf for your OpenStack deployment. For example, the Secret can be generated using the oc create secret generic cloudconfig --from-file cloud.conf --dry-run -o yaml.
    2
    Optionally, add nodeSelector to the CSI driver pod template to configure the nodes on which the CSI driver starts. Only nodes matching the selector run pods that use volumes that are served by the CSI driver. Without nodeSelector, the driver runs on all nodes in the cluster.

2.4.3. Dynamic Provisioning

Dynamic provisioning of persistent storage depends on the capabilities of the CSI driver and underlying storage backend. The provider of the CSI driver should document how to create a StorageClass in OpenShift Container Platform and the parameters available for configuration.

As seen in the OpenStack Cinder example, you can deploy this StorageClass to enable dynamic provisioning.

Procedure

  • Create a default storage class that ensures all PVCs that do not require any special storage class are provisioned by the installed CSI driver.

    # oc create -f - << EOF
    apiVersion: storage.k8s.io/v1
    kind: StorageClass
    metadata:
      name: cinder
      annotations:
        storageclass.kubernetes.io/is-default-class: "true"
    provisioner: csi-cinderplugin
    parameters:
    EOF

2.4.4. Example using the CSI driver

The following example installs a default MySQL template without any changes to the template.

Prerequisites

  • The CSI driver has been deployed.
  • A StorageClass has been created for dynamic provisioning.

Procedure

  • Create the MySQL template:

    # oc new-app mysql-persistent
    --> Deploying template "openshift/mysql-persistent" to project default
    ...
    
    # oc get pvc
    NAME              STATUS    VOLUME                                   CAPACITY
    ACCESS MODES   STORAGECLASS   AGE
    mysql             Bound     kubernetes-dynamic-pv-3271ffcb4e1811e8   1Gi
    RWO            cinder         3s

2.5. Persistent storage using volume snapshots

This document describes how to use VolumeSnapshots to protect against data loss in OpenShift Container Platform. Familiarity with persistent volumes is suggested.

Important

Volume Snapshot is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see https://access.redhat.com/support/offerings/techpreview/.

2.5.1. About snapshots

A volume snapshot is a snapshot taken from a storage volume in a cluster. The external snapshot controller and provisioner enable use of the feature in the OpenShift Container Platform cluster and handle volume snapshots through the OpenShift Container Platform API.

With volume snapshots, a cluster administrator can:

  • Create a snapshot of a PersistentVolume bound to a PersistentVolumeClaim.
  • List existing VolumeSnapshots.
  • Delete an existing VolumeSnapshot.
  • Create a new PersistentVolume from an existing VolumeSnapshot.

Supported PersistentVolume types:

  • AWS Elastic Block Store (EBS)
  • Google Compute Engine (GCE) Persistent Disk (PD)

2.5.2. External controller and provisioner

The controller and provisioner provide volume snapshotting. These external components run in the cluster.

There are two external components that provide volume snapshotting:

External controller
Creates, deletes, and reports events on volume snapshots.
External provisioner
Creates new PersistentVolumes from VolumeSnapshots.

The external controller and provisioner services are distributed as container images and can be run in the OpenShift Container Platform cluster as usual.

2.5.2.1. Running the external controller and provisioner

The cluster administrator must configure access to run the external controller and provisioner.

Procedure

To allow the containers managing the API objects:

  1. Create a ServiceAccount and ClusterRole:

    apiVersion: v1
    kind: ServiceAccount
    metadata:
      name: snapshot-controller-runner
    kind: ClusterRole
    apiVersion: rbac.authorization.k8s.io/v1
    metadata:
      name: snapshot-controller-role
    rules:
      - apiGroups: [""]
        resources: ["persistentvolumes"]
        verbs: ["get", "list", "watch", "create", "delete"]
      - apiGroups: [""]
        resources: ["persistentvolumeclaims"]
        verbs: ["get", "list", "watch", "update"]
      - apiGroups: ["storage.k8s.io"]
        resources: ["storageclasses"]
        verbs: ["get", "list", "watch"]
      - apiGroups: [""]
        resources: ["events"]
        verbs: ["list", "watch", "create", "update", "patch"]
      - apiGroups: ["apiextensions.k8s.io"]
        resources: ["customresourcedefinitions"]
        verbs: ["create", "list", "watch", "delete"]
      - apiGroups: ["volumesnapshot.external-storage.k8s.io"]
        resources: ["volumesnapshots"]
        verbs: ["get", "list", "watch", "create", "update", "patch", "delete"]
      - apiGroups: ["volumesnapshot.external-storage.k8s.io"]
        resources: ["volumesnapshotdatas"]
        verbs: ["get", "list", "watch", "create", "update", "patch", "delete"]
  2. Bind the rules via ClusterRoleBinding:

    apiVersion: rbac.authorization.k8s.io/v1beta1
    kind: ClusterRoleBinding
    metadata:
      name: snapshot-controller
    roleRef:
      apiGroup: rbac.authorization.k8s.io
      kind: ClusterRole
      name: snapshot-controller-role
    subjects:
    - kind: ServiceAccount
      name: snapshot-controller-runner
      namespace: default

2.5.2.2. AWS and GCE authentication

To authenticate the external controller and provisioner, your cloud provider may require the administrator to provide a secret.

2.5.2.2.1. AWS authentication

If the external controller and provisioner are deployed in Amazon Web Services (AWS), AWS must be able to authenticate using the access key.

To provide the credential to the Pod, the cluster administrator creates a new secret:

apiVersion: v1
kind: Secret
metadata:
  name: awskeys
type: Opaque
data:
  access-key-id: <base64 encoded AWS_ACCESS_KEY_ID>
  secret-access-key: <base64 encoded AWS_SECRET_ACCESS_KEY>

The following example displays the AWS deployment of the external controller and provisioner containers. Both Pod containers use the secret to access the AWS API.

kind: Deployment
apiVersion: extensions/v1beta1
metadata:
  name: snapshot-controller
spec:
  replicas: 1
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: snapshot-controller
    spec:
      serviceAccountName: snapshot-controller-runner
      containers:
        - name: snapshot-controller
          image: "registry.redhat.io/openshift3/snapshot-controller:latest"
          imagePullPolicy: "IfNotPresent"
          args: ["-cloudprovider", "aws"]
          env:
            - name: AWS_ACCESS_KEY_ID
              valueFrom:
                secretKeyRef:
                  name: awskeys
                  key: access-key-id
            - name: AWS_SECRET_ACCESS_KEY
              valueFrom:
                secretKeyRef:
                  name: awskeys
                  key: secret-access-key
        - name: snapshot-provisioner
          image: "registry.redhat.io/openshift3/snapshot-provisioner:latest"
          imagePullPolicy: "IfNotPresent"
          args: ["-cloudprovider", "aws"]
          env:
            - name: AWS_ACCESS_KEY_ID
              valueFrom:
                secretKeyRef:
                  name: awskeys
                  key: access-key-id
            - name: AWS_SECRET_ACCESS_KEY
              valueFrom:
                secretKeyRef:
                  name: awskeys
                  key: secret-access-key
2.5.2.2.2. GCE authentication

For Google Compute Engine (GCE), there is no need to use secrets to access the GCE API.

The administrator can proceed with the deployment as shown in the following example:

kind: Deployment
apiVersion: extensions/v1beta1
metadata:
  name: snapshot-controller
spec:
  replicas: 1
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: snapshot-controller
    spec:
      serviceAccountName: snapshot-controller-runner
      containers:
        - name: snapshot-controller
          image: "registry.redhat.io/openshift3/snapshot-controller:latest"
          imagePullPolicy: "IfNotPresent"
          args: ["-cloudprovider", "gce"]
        - name: snapshot-provisioner
          image: "registry.redhat.io/openshift3/snapshot-provisioner:latest"
          imagePullPolicy: "IfNotPresent"
          args: ["-cloudprovider", "gce"]

2.5.2.3. Managing snapshot users

Depending on the cluster configuration, it might be necessary to allow non-administrator users to manipulate the VolumeSnapshot objects on the API server. This can be done by creating a ClusterRole bound to a particular user or group.

For example, assume the user "alice" needs to work with snapshots in the cluster. The cluster administrator completes the following steps:

  1. Define a new ClusterRole:

    apiVersion: v1
    kind: ClusterRole
    metadata:
      name: volumesnapshot-admin
    rules:
    - apiGroups:
      - "volumesnapshot.external-storage.k8s.io"
      attributeRestrictions: null
      resources:
      - volumesnapshots
      verbs:
      - create
      - delete
      - deletecollection
      - get
      - list
      - patch
      - update
      - watch
  2. Bind the cluster role to the user "alice" by creating a ClusterRole binding object:

    apiVersion: rbac.authorization.k8s.io/v1beta1
    kind: ClusterRoleBinding
    metadata:
      name: volumesnapshot-admin
    roleRef:
      apiGroup: rbac.authorization.k8s.io
      kind: ClusterRole
      name: volumesnapshot-admin
    subjects:
    - kind: User
      name: alice
Note

This is only an example of API access configuration. The VolumeSnapshot objects behave similar to other OpenShift Container Platform API objects. See the API access control documentation for more information on managing the API RBAC.

2.5.3. Creating and deleting snapshots

Similar to how a persistent volume claim (PVC) binds to a persistent volume (PV) to provision a volume, VolumeSnapshotData and VolumeSnapshot are used to create a volume snapshot.

Volume snapshots must use a supported PersistentVolume type.

2.5.3.1. Create snapshot

To take a snapshot of a PV, create a new VolumeSnapshotData object based on the VolumeSnapshot, as shown in the following example:

apiVersion: volumesnapshot.external-storage.k8s.io/v1
kind: VolumeSnapshot 1
metadata:
  name: snapshot-demo
spec:
  persistentVolumeClaimName: ebs-pvc 2
1
A VolumeSnapshotData object is automatically created based on the VolumeSnapshot.
2
persistentVolumeClaimName is the name of the PersistentVolumeClaim bound to a PersistentVolume. This particular PV is snapshotted.

Depending on the PV type, the create snapshot operation might go through several phases, which are reflected by the VolumeSnapshot status:

  1. Create the new VolumeSnapshot object.
  2. Start the controller. The snapshotted PersistentVolume might need to be frozen and the applications paused.
  3. Create ("cut") the snapshot. The snapshotted PersistentVolume might return to normal operation, but the snapshot itself is not yet ready (status=True, type=Pending).
  4. Create the new VolumeSnapshotData object, representing the actual snapshot.
  5. The snapshot is complete and ready to use (status=True, type=Ready).
Important

It is the user’s responsibility to ensure data consistency (stop the Pod or application, flush caches, freeze the file system, and so on).

Note

In case of error, the VolumeSnapshot status is appended with an Error condition.

To display the VolumeSnapshot status:

$ oc get volumesnapshot -o yaml

The status is displayed, as shown in the following example:

apiVersion: volumesnapshot.external-storage.k8s.io/v1
kind: VolumeSnapshot
metadata:
  clusterName: ""
  creationTimestamp: 2017-09-19T13:58:28Z
  generation: 0
  labels:
    Timestamp: "1505829508178510973"
  name: snapshot-demo
  namespace: default
  resourceVersion: "780"
  selfLink: /apis/volumesnapshot.external-storage.k8s.io/v1/namespaces/default/volumesnapshots/snapshot-demo
  uid: 9cc5da57-9d42-11e7-9b25-90b11c132b3f
spec:
  persistentVolumeClaimName: ebs-pvc
  snapshotDataName: k8s-volume-snapshot-9cc8813e-9d42-11e7-8bed-90b11c132b3f
status:
  conditions:
  - lastTransitionTime: null
    message: Snapshot created successfully
    reason: ""
    status: "True"
    type: Ready
  creationTimestamp: null

2.5.3.2. Restore snapshot

A PVC is used to restore a snapshot. But first, the administrator must create a StorageClass to restore a PersistentVolume from an existing VolumeSnapshot.

  1. Create a StorageClass:

    kind: StorageClass
    apiVersion: storage.k8s.io/v1
    metadata:
      name: snapshot-promoter
    provisioner: volumesnapshot.external-storage.k8s.io/snapshot-promoter
  2. Create a PVC:

    apiVersion: v1
    kind: PersistentVolumeClaim
    metadata:
      name: snapshot-pv-provisioning-demo
      annotations:
        snapshot.alpha.kubernetes.io/snapshot: snapshot-demo 1
    spec:
      storageClassName: snapshot-promoter 2
    1
    The name of the VolumeSnapshot to be restored.
    2
    Created by the administrator for restoring VolumeSnapshots.

    A new PersistentVolume is created and bound to the PersistentVolumeClaim. The process might take several minutes depending on the PV type.

2.5.3.3. Delete snapshot

To delete a VolumeSnapshot:

$ oc delete volumesnapshot/<snapshot-name>

The VolumeSnapshotData bound to the VolumeSnapshot is automatically deleted.

Chapter 3. Expanding persistent volumes

3.1. Enabling volume expansion support

Before you can expand persistent volumes, the StorageClass must have the allowVolumeExpansion field set to true.

Procedure

  • Edit the StorageClass and add the allowVolumeExpansion attribute. The following example demonstrates adding this line at the bottom of the StorageClass’s configuration.

    apiVersion: storage.k8s.io/v1
    kind: StorageClass
    ...
    parameters:
      type: gp2
    reclaimPolicy: Delete
    allowVolumeExpansion: true 1
    1
    Setting this attribute to true allows PVCs to be expanded after creation.

3.2. Expanding Persistent Volume Claims (PVC) with a file system

Expanding PVCs based on volume types that need file system resizing, such as GCE, PD, EBS, and Cinder, is a two-step process. This process involves expanding volume objects in the cloud provider, and then expanding the file system on the actual node.

Expanding the file system on the node only happens when a new pod is started with the volume.

Prerequisites

  • The controlling StorageClass must have allowVolumeExpansion set to true.

Procedure

  1. Edit the PVC and request a new size by editing spec.resources.requests. For example, the following expands the ebs PVC to 8 Gi.

    kind: PersistentVolumeClaim
    apiVersion: v1
    metadata:
      name: ebs
    spec:
      storageClass: "storageClassWithFlagSet"
      accessModes:
        - ReadWriteOnce
      resources:
        requests:
          storage: 8Gi 1
    1
    Updating spec.resources.requests to a larger amount will expand the PVC.
  2. Once the cloud provider object has finished resizing, the PVC is set to FileSystemResizePending. The following command is used to check the condition:

    $ oc describe pvc <pvc_name>
  3. When the cloud provider object has finished resizing, the persistent volume object reflects the newly requested size in PersistentVolume.Spec.Capacity. At this point, you can create or re-create a new pod from the PVC to finish the file system resizing. Once the pod is running, the newly requested size is available and the FileSystemResizePending condition is removed from the PVC.

3.3. Recovering from Failure when Expanding Volumes

If expanding underlying storage fails, the OpenShift Container Platform administrator can manually recover the Persistent Volume Claim (PVC) state and cancel the resize requests. Otherwise, the resize requests are continuously retried by the controller without administrator intervention.

Procedure

  1. Mark the persistent volume (PV) that is bound to the PVC with the Retain reclaim policy. This can be done by editing the PV and changing persistentVolumeReclaimPolicy to Retain.
  2. Delete the PVC. This will be recreated later.
  3. To ensure that the newly created PVC can bind to the PV marked Retain, manually edit the PV and delete the claimRef entry from the PV specs. This marks the PV as Available.
  4. Re-create the PVC in a smaller size, or a size that can be allocated by the underlying storage provider.
  5. Set the volumeName field of the PVC to the name of the PV. This binds the PVC to the provisioned PV only.
  6. Restore the reclaim policy on the PV.

Chapter 4. Dynamic provisioning

4.1. About dynamic provisioning

The StorageClass resource object describes and classifies storage that can be requested, as well as provides a means for passing parameters for dynamically provisioned storage on demand. StorageClass objects can also serve as a management mechanism for controlling different levels of storage and access to the storage. Cluster Administrators (cluster-admin) or Storage Administrators (storage-admin) define and create the StorageClass objects that users can request without needing any intimate knowledge about the underlying storage volume sources.

The OpenShift Container Platform persistent volume framework enables this functionality and allows administrators to provision a cluster with persistent storage. The framework also gives users a way to request those resources without having any knowledge of the underlying infrastructure.

Many storage types are available for use as persistent volumes in OpenShift Container Platform. While all of them can be statically provisioned by an administrator, some types of storage are created dynamically using the built-in provider and plug-in APIs.

4.2. Available dynamic provisioning plug-ins

OpenShift Container Platform provides the following provisioner plug-ins, which have generic implementations for dynamic provisioning that use the cluster’s configured provider’s API to create new storage resources:

Storage typeProvisioner plug-in nameNotes

AWS Elastic Block Store (EBS)

kubernetes.io/aws-ebs

For dynamic provisioning when using multiple clusters in different zones, tag each node with Key=kubernetes.io/cluster/<cluster_name>,Value=<cluster_id> where <cluster_name> and <cluster_id> are unique per cluster.

Important

Any chosen provisioner plug-in also requires configuration for the relevant cloud, host, or third-party provider as per the relevant documentation.

4.3. Defining a StorageClass

StorageClass objects are currently a globally scoped object and must be created by cluster-admin or storage-admin users.

Note

For AWS, a default StorageClass is created during OpenShift Container Platform installation. You can change the default StorageClass after installation, but the created StorageClass cannot be deleted.

The following sections describe the basic object definition for a StorageClass and specific examples for each of the supported plug-in types.

4.3.1. Basic StorageClass object definition

The following resource shows the parameters and default values that you use to configure a StorageClass. This example uses the AWS ElasticBlockStore (EBS) object definition.

Sample StorageClass definition

kind: StorageClass 1
apiVersion: storage.k8s.io/v1 2
metadata:
  name: gp2 3
  annotations: 4
    storageclass.kubernetes.io/is-default-class: 'true'
    ...
provisioner: kubernetes.io/aws-ebs 5
parameters: 6
  type: gp2
...

1
(required) The API object type.
2
(required) The current apiVersion.
3
(required) The name of the StorageClass.
4
(optional) Annotations for the StorageClass
5
(required) The type of provisioner associated with this storage class.
6
(optional) The parameters required for the specific provisioner, this will change from plug-in to plug-in.

4.3.2. StorageClass annotations

To set a StorageClass as the cluster-wide default, add the following annotation to your StorageClass’s metadata:

storageclass.kubernetes.io/is-default-class: "true"

For example:

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  annotations:
    storageclass.kubernetes.io/is-default-class: "true"
...

This enables any Persistent Volume Claim (PVC) that does not specify a specific volume to automatically be provisioned through the default StorageClass.

Note

The beta annotation storageclass.beta.kubernetes.io/is-default-class is still working; however, it will be removed in a future release.

To set a StorageClass description, add the following annotation to your StorageClass’s metadata:

kubernetes.io/description: My StorageClass Description

For example:

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  annotations:
    kubernetes.io/description: My StorageClass Description
...

4.3.3. AWS Elastic Block Store (EBS) object definition

aws-ebs-storageclass.yaml

kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: slow
provisioner: kubernetes.io/aws-ebs
parameters:
  type: io1 1
  zone: us-east-1d 2
  iopsPerGB: "10" 3
  encrypted: "true" 4
  kmsKeyId: keyvalue 5
  fsType: ext4 6

1
(required) Select from io1, gp2, sc1, st1. The default is gp2. See the AWS documentation for valid Amazon Resource Name (ARN) values.
2
(optional) The AWS zone. If no zone is specified, volumes are generally round-robined across all active zones where the OpenShift Container Platform cluster has a node. The zone and zones parameters must not be used at the same time.
3
(optional) Only for io1 volumes. I/O operations per second per GiB. The AWS volume plug-in multiplies this with the size of the requested volume to compute IOPS of the volume. The value cap is 20,000 IOPS, which is the maximum supported by AWS. See the AWS documentation for further details.
4
(optional) Denotes whether to encrypt the EBS volume. Valid values are true or false.
5
(optional) The full ARN of the key to use when encrypting the volume. If none is supplied, but encypted is set to true, then AWS generates a key. See the AWS documentation for a valid ARN value.
6
(optional) File system that is created on dynamically provisioned volumes. This value is copied to the fsType field of dynamically provisioned persistent volumes and the file system is created when the volume is mounted for the first time. The default value is ext4.

4.4. Changing the default StorageClass

If you are using AWS, use the following process to change the default StorageClass. This process assumes you have two StorageClasses defined, gp2 and standard, and you want to change the default StorageClass from gp2 to standard.

  1. List the StorageClass:

    $ oc get storageclass
    
    NAME                 TYPE
    gp2 (default)        kubernetes.io/aws-ebs 1
    standard             kubernetes.io/aws-ebs
    1
    (default) denotes the default StorageClass.
  2. Change the value of the annotation storageclass.kubernetes.io/is-default-class to false for the default StorageClass:

    $ oc patch storageclass gp2 -p '{"metadata": {"annotations": {"storageclass.kubernetes.io/is-default-class": "false"}}}'
  3. Make another StorageClass the default by adding or modifying the annotation as storageclass.kubernetes.io/is-default-class=true.

    $ oc patch storageclass standard -p '{"metadata": {"annotations": {"storageclass.kubernetes.io/is-default-class": "true"}}}'
  4. Verify the changes:

    $ oc get storageclass
    
    NAME                 TYPE
    gp2                  kubernetes.io/aws-ebs
    standard (default)   kubernetes.io/aws-ebs

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