Chapter 3. Verify Prerequisites

This chapter provides the prerequisites that have to be verified before for the two different use cases available in Containerized Red Hat Gluster Storage before deployment.

3.1. Converged mode

3.1.1. Supported Versions

The following table lists the supported versions of OpenShift Container Platform with Red Hat Gluster Storage Server and Red Hat Openshift Container Storage.

Table 3.1. Supported Versions

OpenShift Container PlatformRed Hat Gluster StorageRed Hat Openshift Container Storage / Openshift Container Storage
3.113.43.10, 3.11
3.103.43.9, 3.10
3.7, 3.9, 3.103.3.1 3.9

3.1.2. Environment Requirements

The requirements for Red Hat Enterprise Linux Atomic Host, Red Hat OpenShift Container Platform, Red Hat Enterprise Linux, and Red Hat Gluster Storage are described in this section. A Red Hat Gluster Storage Container Native with OpenShift Container Platform environment consists of Red Hat OpenShift Container Platform installed on either Red Hat Enterprise Linux Atomic Host or Red Hat Enterprise Linux.

3.1.2.1. Installing Red Hat Openshift Container Storage with OpenShift Container Platform on Red Hat Enterprise Linux 7

This section describes the procedures to install Red Hat Gluster Storage Container Native with OpenShift Container Platform on Red Hat Enterprise Linux 7 based OpenShift Container Platform 3.10.
3.1.2.1.1. Setting up the Openshift Master as the Client
You can use the OpenShift Master as a client to execute the oc commands across the cluster when installing OpenShift. Generally, this is setup as a non-scheduled node in the cluster. This is the default configuration when using the OpenShift installer. You can also choose to install their client on their local machine to access the cluster remotely. For more information, see https://access.redhat.com/documentation/en-us/openshift_container_platform/3.10/html/cli_reference/cli-reference-get-started-cli#installing-the-cli.
Install heketi-client package

Execute the following commands to install heketi-client package. 

# subscription-manager repos --enable=rh-gluster-3-client-for-rhel-7-server-rpms
# yum install heketi-client
After installing the heketi-client package, disable the gluster repo by executing the following command: 
# subscription-manager repos --disable=rh-gluster-3-client-for-rhel-7-server-rpms

3.1.3. Red Hat OpenShift Container Platform and Red Hat Openshift Container Storage Requirements

The following list provides the Red Hat OpenShift Container Platform and Red Hat Openshift Container Storage requirements:

3.1.4. Red Hat Gluster Storage Requirements

The following list provides the details regarding the Red Hat Gluster Storage requirements:
  • Installation of Heketi packages must have valid subscriptions to Red Hat Gluster Storage Server repositories.
  • Red Hat Gluster Storage installations must adhere to the requirements outlined in the Red Hat Gluster Storage Installation Guide.
  • The versions of Red Hat Enterprise OpenShift and Red Hat Gluster Storage integrated must be compatible, according to the information in Section 3.1.1, “Supported Versions” section.
  • A fully qualified domain name must be set for Red Hat Gluster Storage server node. Ensure that the correct DNS records exist, and that the fully qualified domain name is resolvable via both forward and reverse DNS lookup.
  • To access GlusterFS volumes, the mount.glusterfs command must be available on all schedulable nodes. For RPM-based systems, the glusterfs-fuse package must be installed: 
    # yum install glusterfs-fuse
    This package comes installed on every RHEL system. However, it is recommended to update to the latest available version from Red Hat Gluster Storage. To do this, the following RPM repository must be enabled: 
    # subscription-manager repos --enable=rh-gluster-3-client-for-rhel-7-server-rpms
    If glusterfs-fuse is already installed on the nodes, ensure that the latest version is installed: 
    # yum update glusterfs-fuse

Important

Restrictions for using Snapshot

  • After a snapshot is created, it must be accessed through the user-serviceable snapshots feature only. This can be used to copy the old versions of files into the required location.
    Reverting the volume to a snapshot state is not supported and should never be done as it might damage the consistency of the data.
  • On a volume with snapshots, volume changing operations, such as volume expansion, must not be performed.

3.1.5. Deployment and Scaling Guidelines

To prevent potential deployment or scaling issues, review the following guidelines before deploying converged mode or independent mode with OpenShift Container Platform.
Ensure that the Trusted Storage Pool is appropriately sized and you have room for dynamic scaling on demand. This action ensures that you do not scale beyond the following maximum limits:
  • Sizing guidelines on converged mode or independent mode:
    • Persistent volumes backed by the file interface: For typical operations, size for 300-500 persistent volumes backed by files per three-node converged mode or independent mode cluster. The maximum limit of supported persistent volumes backed by the file interface is 1000 persistent volumes per three-node cluster in a converged mode or independent mode deployment. Considering that micro-services can dynamically scale as per demand, it is recommended that the initial sizing keep sufficient headroom for the scaling. If additional scaling is needed, add a new three-node converged mode or independent mode cluster to support additional persistent volumes
      Creation of more than 1,000 persistent volumes per trusted storage pool is not supported for file-based storage.
    • Persistent volumes backed by block-based storage: Size for a maximum of 300 persistent volumes per three-node converged mode or independent mode cluster. Be aware that converged mode and independent mode supports only OpenShift Container Platform logging and metrics on block-backed persistent volumes.
    • Persistent volumes backed by file and block: Size for 300-500 persistent volumes (backed by files) and 100-200 persistent volumes (backed by block). Do not exceed these maximum limits of file or block-backed persistent volumes or the combination of a maximum 1000 persistent volumes per three-node converged mode or independent mode cluster.
    • 3-way distributed-replicated volumes and arbitrated volumes are the only supported volume typesS.
    • Minimum Red Hat Openshift Container Storage cluster size (4): It is recommended to have a minimum of 4 nodes in the Red Hat Openshift Container Storage cluster to adequately meet high-availability requirements. Although 3 nodes are required to create a persistent volume claim, the failure of one node in a 3 node cluster prevents the persistent volume claim from being created. The fourth node provides high-availability and allows the persistent volume claim to be created even if a node fails.
    • Each physical or virtual node that hosts a converged mode or independent mode peer requires the following:
      • a minimum of 8 GB RAM and 30 MB per persistent volume.
      • the same disk type.
      • the heketidb utilises 2 GB distributed replica volume.
  • Deployment guidelines on converged mode or independent mode:
    • In converged mode, you can install the Red Hat Openshift Container Storage nodes, Heketi, and all provisioner pods on OpenShift Container Platform Infrastructure nodes or OpenShift Container Platform Application nodes.
    • In independent mode, you can install Heketi and all provisioners pods on OpenShift Container Platform Infrastructure nodes or on OpenShift Container Platform Application nodes
  • Red Hat Gluster Storage Container Native with OpenShift Container Platform supports up to 14 snapshots per volume by default (snap-max-hard-limit =14 in Heketi Template).