Chapter 9. Caching images for faster workspace start

This section describes installing the Image Puller on a CodeReady Workspaces cluster to cache images on cluster nodes.

9.1. Image Puller overview

Slow starts of Red Hat CodeReady Workspaces workspaces may be caused by waiting for the underlying cluster to pull images used in workspaces from remote registries. As such, pre-pulling images can improve start times significantly. The Image Puller can be used to pre-pull images and shorten workspace start times.

The Image Puller is an additional deployment that runs alongside Red Hat CodeReady Workspaces. Given a list of images to pre-pull, the application runs inside a cluster and creates a DaemonSet that pulls the images on each node.

Note

The minimal requirement for an image to be pre-pulled is the availability of the sleep command, which means that FROM scratch images (for example, 'che-machine-exec') are currently not supported. Also, images that mount volumes in the dockerfile are not supported for pre-pulling on OpenShift.

The application can be deployed:

The Image Puller loads its configuration from a ConfigMap with the following available parameters:

Table 9.1. Image Puller default parameters

ParameterUsageDefault

CACHING_INTERVAL_HOURS

Interval, in hours, between checking health of DaemonSets

"1"

CACHING_MEMORY_REQUEST

The memory request for each cached image when the puller is running

10Mi

CACHING_MEMORY_LIMIT

The memory limit for each cached image when the puller is running

20Mi

CACHING_CPU_REQUEST

The CPU request for each cached image when the puller is running

.05

CACHING_CPU_LIMIT

The CPU limit for each cached image when the puller is running

.2

DAEMONSET_NAME

Name of DaemonSet to be created

kubernetes-image-puller

NAMESPACE

Namespace where DaemonSet is to be created

k8s-image-puller

IMAGES

List of images to be cached, in the format <name>=<image>;…​

Contains a default list of images. Before deploying, fill this with the images that fit the current requirements

NODE_SELECTOR

Node selector applied to the Pods created by the DaemonSet

'{}'

The default memory requests and limits ensure that the container has enough memory to start. When changing CACHING_MEMORY_REQUEST or CACHING_MEMORY_LIMIT, you will need to consider the total memory allocated to the DaemonSet Pods in the cluster:

(memory limit) * (number of images) * (number of nodes in the cluster)

For example, running the Image Puller that caches 5 images on 20 nodes, with a container memory limit of 20Mi requires 2000Mi of memory.

9.2. Deploying Image Puller using the Operator

The recommended way to deploy the Image Puller is through the Operator.

9.2.1. Installing the Image Puller on OpenShift using OperatorHub

Prerequisites

  • A project in your cluster to host the Image Puller. This document uses the project image-puller as an example.

Procedure

  1. Navigate to your OpenShift cluster console, navigate to Operators → OperatorHub.
  2. Use the Filter by keyword box to search for Kubernetes Image Puller Operator. Click the Kubernetes Image Puller Operator.
  3. Read the description of the Operator. Click Continue → Install.
  4. Select A specific project on the cluster for the Installation Mode. In the drop-down find the project you created to install the Image Puller. Click Subscribe.
  5. Wait for the Kubernetes Image Puller Operator to install. Click the KubernetesImagePuller → Create instance.
  6. In a redirected window with a YAML editor, make modifications to the KubernetesImagePuller Custom Resource and click Create.
  7. Navigate to the Workloads and Pods menu in the project and verify that the Image Puller is available.

9.3. Deploying Image Puller using OpenShift templates

The Image Puller repository contains OpenShift templates for deploying on OpenShift.

Prerequisites

  • A running OpenShift cluster.
  • The oc tool is available.

The following parameters are available to further configure the OpenShift templates:

Table 9.2. Parameters for installing with OpenShift templates

ValueUsageDefault

DAEMONSET_NAME

The value of DAEMONSET_NAME to set in the ConfigMap

kubernetes-image-puller

IMAGE

Image used for the kubernetes-image-puller deployment

registry.redhat.io/codeready-workspaces/imagepuller-rhel8:2.5

IMAGE_TAG

The image tag to pull

2.5

SERVICEACCOUNT_NAME

The name of the ServiceAccount used by the deployment (created as part of installation)

k8s-image-puller

CACHING_INTERVAL_HOURS

The value of CACHING_INTERVAL_HOURS to set in the ConfigMap

"1"

CACHING_INTERVAL_REQUEST

The value of CACHING_MEMORY_REQUEST to set in the ConfigMap

"10Mi"

CACHING_INTERVAL_LIMIT

The value of CACHING_MEMORY_LIMIT to set in the ConfigMap

"20Mi"`

NODE_SELECTOR

The value of NODE_SELECTOR to set in the ConfigMap

"{}"

See Table 9.1, “Image Puller default parameters” for more information about configuration values, such as DAEMONSET_NAME, CACHING_INTERVAL_HOURS, and CACHING_MEMORY_REQUEST.

Table 9.3. List of recommended images to pre-pull

ImageURLTag

theia-rhel8

codeready-workspaces/theia-rhel8

2.5

theia-endpoint-rhel8

theia-endpoint-image

2.5

pluginbroker-metadata-rhel8

registry.redhat.io/codeready-workspaces/pluginbroker-metadata-rhel8:2.5

2.5

pluginbroker-artifacts-rhel8

registry.redhat.io/codeready-workspaces/pluginbroker-artifacts-rhel8:2.5

2.5

plugin-java8-rhel8

registry.redhat.io/codeready-workspaces/plugin-java8-rhel8:2.5

2.5

plugin-java11-rhel8

registry.redhat.io/codeready-workspaces/plugin-java11-rhel8:2.5

2.5

plugin-kubernetes-rhel8

registry.redhat.io/codeready-workspaces/plugin-kubernetes-rhel8:2.5

2.5

plugin-openshift-rhel8

registry.redhat.io/codeready-workspaces/plugin-openshift-rhel8:2.5

2.5

stacks-cpp-rhel8

registry.redhat.io/codeready-workspaces/stacks-cpp-rhel8:2.5

2.5

stacks-dotnet-rhel8

registry.redhat.io/codeready-workspaces/stacks-dotnet-rhel8:2.5

2.5

stacks-golang-rhel8

registry.redhat.io/codeready-workspaces/stacks-golang-rhel8:2.5

2.5

stacks-php-rhel8

registry.redhat.io/codeready-workspaces/stacks-php-rhel8:2.5

2.5

See Table 9.1, “Image Puller default parameters” for more information about configuration values, such as DAEMONSET_NAME, CACHING_INTERVAL_HOURS, and CACHING_MEMORY_REQUEST.

Procedure

Installing

  1. Clone the Kubernetes Image Puller repository: 

    $ git clone https://github.com/che-incubator/kubernetes-image-puller
$ cd kubernetes-image-puller

  2. Create a new OpenShift project to deploy the puller into: 

    $ oc new-project k8s-image-puller

  3. Process and apply the templates to deploy the puller:

    In CodeReady Workspaces you must use custom values to deploy the image puller. To set custom values, add to the oc process an option: -p <parameterName>=<value>: 

    $ oc process -f deploy/openshift/serviceaccount.yaml \
    | oc apply -f -
$ oc process -f deploy/openshift/configmap.yaml \
    -p IMAGES='plugin-java8-rhel8=registry.redhat.io/codeready-workspaces/plugin-java8-rhel8:2.5;\
    theia-rhel8=registry.redhat.io/codeready-workspaces/theia-rhel8:2.5;\
    stacks-golang-rhel8=registry.redhat.io/codeready-workspaces/stacks-golang-rhel8:2.5;\
    plugin-java11-rhel8=registry.redhat.io/codeready-workspaces/plugin-java11-rhel8:2.5;\
    theia-endpoint-rhel8=registry.redhat.io/codeready-workspaces/theia-rhel8:2.5;\
    pluginbroker-metadata-rhel8=registry.redhat.io/codeready-workspaces/pluginbroker-metadata-rhel8:2.5;\
    pluginbroker-artifacts-rhel8=registry.redhat.io/codeready-workspaces/pluginbroker-artifacts-rhel8:2.5;' \
    | oc apply -f -
$ oc process -f deploy/openshift/app.yaml \
    -p IMAGE=registry.redhat.io/codeready-workspaces/imagepuller-rhel8 \
    -p IMAGE_TAG='2.5' \
    | oc apply -f -

Verifying the installation

  1. Confirm that a new deployment, kubernetes-image-puller, and a DaemonSet (named based on the value of the DAEMONSET_NAME parameter) exist. The DaemonSet needs to have a Pod for each node in the cluster: 

    $ oc get deployment,daemonset,pod --namespace k8s-image-puller
deployment.extensions/kubernetes-image-puller   1/1       1            1           2m19s

NAME                                           DESIRED   CURRENT   READY     UP-TO-DATE   AVAILABLE   NODE SELECTOR   AGE
daemonset.extensions/kubernetes-image-puller   1         1         1         1            1           <none>          2m10s

NAME                                           READY     STATUS    RESTARTS   AGE
pod/kubernetes-image-puller-5495f46497-mkd4p   1/1       Running   0          2m18s
pod/kubernetes-image-puller-n8bmf              3/3       Running   0          2m10s

  2. Check that the ConfigMap named k8s-image-puller has the values you specified in your parameter substitution, or that they contain the default values: 

    $ oc get configmap k8s-image-puller --output yaml
apiVersion: v1
data:
  CACHING_INTERVAL_HOURS: "1"
  CACHING_MEMORY_LIMIT: 20Mi
  CACHING_MEMORY_REQUEST: 10Mi
  DAEMONSET_NAME: kubernetes-image-puller
  IMAGES: |
    theia-rhel8=registry.redhat.io/codeready-workspaces/theia-rhel8:{prod-ver};
    theia-endpoint-rhel8=registry.redhat.io/codeready-workspaces/theia-rhel8:{prod-ver};
    pluginbroker-metadata-rhel8=registry.redhat.io/codeready-workspaces/pluginbroker-metadata-rhel8:{prod-ver};
    pluginbroker-artifacts-rhel8=registry.redhat.io/codeready-workspaces/pluginbroker-artifacts-rhel8:{prod-ver};
    plugin-java8-rhel8=registry.redhat.io/codeready-workspaces/plugin-java8-rhel8:{prod-ver};
    plugin-java11-rhel8=registry.redhat.io/codeready-workspaces/plugin-java11-rhel8:{prod-ver};
    stacks-golang-rhel8=registry.redhat.io/codeready-workspaces/stacks-golang-rhel8:{prod-ver};
  NAMESPACE: k8s-image-puller
  NODE_SELECTOR: '{}'
kind: ConfigMap
metadata:
  annotations:
    kubectl.kubernetes.io/last-applied-configuration: |
      {"apiVersion":"v1","data":{"CACHING_INTERVAL_HOURS":"1","CACHING_MEMORY_LIMIT":"20Mi","CACHING_MEMORY_REQUEST":"10Mi","DAEMONSET_NAME":"kubernetes-image-puller","IMAGES":"theia-rhel8=registry.redhat.io/codeready-workspaces/theia-rhel8:{prod-ver}; theia-endpoint-rhel8=registry.redhat.io/codeready-workspaces/theia-rhel8:{prod-ver}; pluginbroker-metadata-rhel8=registry.redhat.io/codeready-workspaces/pluginbroker-metadata-rhel8:{prod-ver}; pluginbroker-artifacts-rhel8=registry.redhat.io/codeready-workspaces/pluginbroker-artifacts-rhel8:{prod-ver}; plugin-java8-rhel8=registry.redhat.io/codeready-workspaces/plugin-java8-rhel8:{prod-ver}; plugin-java11-rhel8=registry.redhat.io/codeready-workspaces/plugin-java11-rhel8:{prod-ver}; stacks-golang-rhel8=registry.redhat.io/codeready-workspaces/stacks-golang-rhel8:{prod-ver};\n","NAMESPACE":"k8s-image-puller","NODE_SELECTOR":"{}"},"kind":"ConfigMap","metadata":{"annotations":{},"name":"k8s-image-puller","namespace":"k8s-image-puller"},"type":"Opaque"}
  creationTimestamp: 2020-02-17T22:40:13Z
  name: k8s-image-puller
  namespace: k8s-image-puller
  resourceVersion: "72250"
  selfLink: /api/v1/namespaces/k8s-image-puller/configmaps/k8s-image-puller
  uid: 76430ed6-51d6-11ea-9c19-52fdfc072182