Chapter 13. Managing Images

Keeping in mind that an image stream in OpenShift Container Platform comprises zero or more container images identified by tags, you can add tags to an image stream using the oc tag command:

$ oc tag <source> <destination>

For example, to configure the ruby imagestream’s static-2.0 tag to always refer to the current image for the ruby imagestream’s 2.0 tag:

$ oc tag ruby:2.0 ruby:static-2.0

This creates a new imagestream tag named static-2.0 in the ruby imagestream. The new tag directly reference the image id that the ruby:2.0 imagestream tag pointed to at the time oc tag was run, and the image it points to never changes.

There are different types of tags available. The default behavior uses a permanent tag, which points to a specific image in time; even when the source changes, the new (destination) tag does not change.

A tracking tag means the destination tag’s metadata is updated during the import of the source tag. To ensure the destination tag is updated whenever the source tag changes, use the --alias=true flag:

$ oc tag --alias=true <source> <destination>

You can also add the --scheduled=true flag to have the destination tag be refreshed (i.e., re-imported) periodically. The period is configured globally at the system level.

See Importing Tag and Image Metadata for more details.

If you want to instruct Docker to always fetch the tagged image from the integrated registry, use --reference-policy=local. The registry uses the pull-through feature pull-through feature to serve the image to the client. By default, the image blobs are mirrored locally by the registry. As a result, they can be pulled more quickly the next time they are needed. The flag also allows for pulling from insecure registries without a need to supply --insecure-registry to the Docker daemon as long as the image stream has an insecure annotation or the tag has an insecure import policy.

Images evolve over time and their tags reflect this. An image tag always points to the latest image built.

If there is too much information embedded in a tag name (for example, v2.0.1-may-2016), the tag points to just one revision of an image and is never updated. Using default image pruning options, such an image is never removed. In very large clusters, the schema of creating new tags for every revised image could eventually fill up the etcd datastore with excess tag metadata for images that are long outdated.

Instead, if the tag is named v2.0, more image revisions are more likely. This results in longer tag history and, therefore, the image pruner is more likely to remove old and unused images. Refer to Pruning Images for more information.

Although tag naming convention is up to you, here are a few examples in the format <image_name>:<image_tag>:

If you require dates in tag names, periodically inspect old and unsupported images and istags and remove them. Otherwise, you might experience increasing resource usage caused by old images.

To remove a tag completely from an image stream run:

$ oc delete istag/ruby:latest

or:

$ oc tag -d ruby:latest

Images can be referenced in image streams using the following reference types:

When viewing example image stream definitions, such as the example CentOS image streams, you may notice they contain definitions of ImageStreamTag and references to DockerImage, but nothing related to ImageStreamImage.

This is because the ImageStreamImage objects are automatically created in OpenShift Container Platform whenever you import or tag an image into the image stream. You should never have to explicitly define an ImageStreamImage object in any image stream definition that you use to create image streams.

You can view an image’s object definition by retrieving an ImageStreamImage definition using the image stream name and ID:

$ oc export isimage <image_stream_name>@<id>

$ oc describe is <image_stream_name>

For example, from the ruby image stream asking for the ImageStreamImage with the name and ID of ruby@3a335d7:

$ oc export isimage ruby@3a335d7

apiVersion: v1
image:
  dockerImageLayers:
  - name: sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
    size: 0
  - name: sha256:ee1dd2cb6df21971f4af6de0f1d7782b81fb63156801cfde2bb47b4247c23c29
    size: 196634330
  - name: sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
    size: 0
  - name: sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
    size: 0
  - name: sha256:ca062656bff07f18bff46be00f40cfbb069687ec124ac0aa038fd676cfaea092
    size: 177723024
  - name: sha256:63d529c59c92843c395befd065de516ee9ed4995549f8218eac6ff088bfa6b6e
    size: 55679776
  dockerImageMetadata:
    Architecture: amd64
    Author: SoftwareCollections.org <sclorg@redhat.com>
    Config:
      Cmd:
      - /bin/sh
      - -c
      - $STI_SCRIPTS_PATH/usage
      Entrypoint:
      - container-entrypoint
      Env:
      - PATH=/opt/app-root/src/bin:/opt/app-root/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
      - STI_SCRIPTS_URL=image:///usr/libexec/s2i
      - STI_SCRIPTS_PATH=/usr/libexec/s2i
      - HOME=/opt/app-root/src
      - BASH_ENV=/opt/app-root/etc/scl_enable
      - ENV=/opt/app-root/etc/scl_enable
      - PROMPT_COMMAND=. /opt/app-root/etc/scl_enable
      - RUBY_VERSION=2.2
      ExposedPorts:
        8080/tcp: {}
      Image: d9c3abc5456a9461954ff0de8ae25e0e016aad35700594714d42b687564b1f51
      Labels:
        build-date: 2015-12-23
        io.k8s.description: Platform for building and running Ruby 2.2 applications
        io.k8s.display-name: Ruby 2.2
        io.openshift.builder-base-version: 8d95148
        io.openshift.builder-version: 8847438ba06307f86ac877465eadc835201241df
        io.openshift.s2i.scripts-url: image:///usr/libexec/s2i
        io.openshift.tags: builder,ruby,ruby22
        io.s2i.scripts-url: image:///usr/libexec/s2i
        license: GPLv2
        name: CentOS Base Image
        vendor: CentOS
      User: "1001"
      WorkingDir: /opt/app-root/src
    ContainerConfig: {}
    Created: 2016-01-26T21:07:27Z
    DockerVersion: 1.8.2-el7
    Id: 57b08d979c86f4500dc8cad639c9518744c8dd39447c055a3517dc9c18d6fccd
    Parent: d9c3abc5456a9461954ff0de8ae25e0e016aad35700594714d42b687564b1f51
    Size: 430037130
    apiVersion: "1.0"
    kind: DockerImage
  dockerImageMetadataVersion: "1.0"
  dockerImageReference: centos/ruby-22-centos7@sha256:3a335d7d8a452970c5b4054ad7118ff134b3a6b50a2bb6d0c07c746e8986b28e
  metadata:
    creationTimestamp: 2016-01-29T13:17:45Z
    name: sha256:3a335d7d8a452970c5b4054ad7118ff134b3a6b50a2bb6d0c07c746e8986b28e
    resourceVersion: "352"
    uid: af2e7a0c-c68a-11e5-8a99-525400f25e34
kind: ImageStreamImage
metadata:
  creationTimestamp: null
  name: ruby@3a335d7
  namespace: openshift
  selflink: /oapi/v1/namespaces/openshift/imagestreamimages/ruby@3a335d7

When using the internal registry, to allow pods in project-a to reference images in project-b, a service account in project-a must be bound to the system:image-puller role in project-b:

$ oc policy add-role-to-user \
    system:image-puller system:serviceaccount:project-a:default \
    --namespace=project-b

After adding that role, the pods in project-a that reference the default service account is able to pull images from project-b.

To allow access for any service account in project-a, use the group:

$ oc policy add-role-to-group \
    system:image-puller system:serviceaccounts:project-a \
    --namespace=project-b

The .dockercfg file (or $HOME/.docker/config.json for newer Docker clients) is a Docker credentials file that stores your information if you have previously logged into a secured or insecure registry.

To pull a secured container image that is not from OpenShift Container Platform’s internal registry, you must create a pull secret from your Docker credentials and add it to your service account.

If you already have a .dockercfg file for the secured registry, you can create a secret from that file by running:

$ oc secrets new <pull_secret_name> .dockercfg=<path/to/.dockercfg>

Or if you have a $HOME/.docker/config.json file:

$ oc secrets new <pull_secret_name> .dockerconfigjson=<path/to/.docker/config.json>

If you do not already have a Docker credentials file for the secured registry, you can create a secret by running:

$ oc secrets new-dockercfg <pull_secret_name> \
    --docker-server=<registry_server> --docker-username=<user_name> \
    --docker-password=<password> --docker-email=<email>

To use a secret for pulling images for pods, you must add the secret to your service account. The name of the service account in this example should match the name of the service account the pod uses; default is the default service account:

$ oc secrets link default <pull_secret_name> --for=pull

To use a secret for pushing and pulling build images, the secret must be mountable inside of a pod. You can do this by running:

$ oc secrets link builder <pull_secret_name>

An image stream can be configured to import tag and image metadata from insecure image registries, such as those signed with a self-signed certificate or using plain HTTP instead of HTTPS.

To configure this, add the openshift.io/image.insecureRepository annotation and set it to true. This setting bypasses certificate validation when connecting to the registry:

kind: ImageStream
apiVersion: v1
metadata:
  name: ruby
  annotations:
    openshift.io/image.insecureRepository: "true" 1
  spec:
    dockerImageRepository: my.repo.com:5000/myimage

kind: ImageStream
apiVersion: v1
metadata:
  name: ruby
  tags:
  - from:
      kind: DockerImage
      name: my.repo.com:5000/myimage
    name: mytag
    importPolicy:
      insecure: true 1
    referencePolicy:
      type: Local 2

An image stream can be configured to import tag and image metadata from private image registries, requiring authentication.

To configure this, you need to create a secret, which is used to store your credentials. See Allowing Pods to Reference Images from Other Secured Registries for instructions on creating a secret using oc create secret command.

After the secret is configured, proceed with creating the new image stream or using the oc import-image command. During the import process, OpenShift Container Platform picks up the secrets and provide them to the remote party.

If the registry you are importing from is using a certificate that is not signed by a standard certificate authority, you need to explicitly configure the system to trust the registry’s certificate or signing authority. This can be done by adding the CA certificate or registry certificate to the host system running the registry import controller (typically the master node).

The certificate or CA certificate must be added to /etc/pki/tls/certs or /etc/pki/ca-trust, respectively, on the host system. The update-ca-trust command also needs to be run on Red Hat distributions followed by a restart of the master service to pick up the certificate changes.

An image stream can be configured to import tag and image metadata from the internal registry, but from a different project. The recommended method for this is to use the oc tag command as shown in Adding Tags to Image Streams:

$ oc tag <source_project>/<image_stream>:<tag> <new_image_stream>:<new_tag>

Another method is to import the image from the other project manually using the pull spec:

An image stream can also be automatically created by manually pushing an image to the internal registry. This is only possible when using an OpenShift Container Platform internal registry.

Before performing this procedure, the following must be satisfied:

To create an image stream by manually pushing an image: