Chapter 6. Managing image streams

Procedure

• To get general information about the image stream and detailed information about all the tags it is pointing to, enter the following command:

  $ oc describe is/<image-name>

  For example:

  $ oc describe is/python

  Example output

  Name:			python
  Namespace:		default
  Created:		About a minute ago
  Labels:			<none>
  Annotations:		openshift.io/image.dockerRepositoryCheck=2017-10-02T17:05:11Z
  Docker Pull Spec:	docker-registry.default.svc:5000/default/python
  Image Lookup:		local=false
  Unique Images:		1
  Tags:			1
  
  3.5
    tagged from centos/python-35-centos7
  
    * centos/python-35-centos7@sha256:49c18358df82f4577386404991c51a9559f243e0b1bdc366df25
        About a minute ago

• To get all of the information available about a particular image stream tag, enter the following command:

  $ oc describe istag/<image-stream>:<tag-name>

  For example:

  $ oc describe istag/python:latest

  Example output

  Image Name:	sha256:49c18358df82f4577386404991c51a9559f243e0b1bdc366df25
  Docker Image:	centos/python-35-centos7@sha256:49c18358df82f4577386404991c51a9559f243e0b1bdc366df25
  Name:		sha256:49c18358df82f4577386404991c51a9559f243e0b1bdc366df25
  Created:	2 minutes ago
  Image Size:	251.2 MB (first layer 2.898 MB, last binary layer 72.26 MB)
  Image Created:	2 weeks ago
  Author:		<none>
  Arch:		amd64
  Entrypoint:	container-entrypoint
  Command:	/bin/sh -c $STI_SCRIPTS_PATH/usage
  Working Dir:	/opt/app-root/src
  User:		1001
  Exposes Ports:	8080/tcp
  Docker Labels:	build-date=20170801

  Note

  More information is output than shown.

• Enter the following command to discover which architecture or operating system that an image stream tag supports:

  $ oc get istag <image-stream-tag> -ojsonpath="{range .image.dockerImageManifests[*]}{.os}/{.architecture}{'\n'}{end}"

  For example:

  $ oc get istag busybox:latest -ojsonpath="{range .image.dockerImageManifests[*]}{.os}/{.architecture}{'\n'}{end}"

  Example output

  linux/amd64
  linux/arm
  linux/arm64
  linux/386
  linux/mips64le
  linux/ppc64le
  linux/riscv64
  linux/s390x

Procedure

• Add a tag that points to one of the existing tags by using the `oc tag`command:

  $ oc tag <image-name:tag1> <image-name:tag2>

  For example:

  $ oc tag python:3.5 python:latest

  Example output

  Tag python:latest set to python@sha256:49c18358df82f4577386404991c51a9559f243e0b1bdc366df25.

• Confirm the image stream has two tags, one, 3.5, pointing at the external container image and another tag, latest, pointing to the same image because it was created based on the first tag.

  $ oc describe is/python

  Example output

  Name:			python
  Namespace:		default
  Created:		5 minutes ago
  Labels:			<none>
  Annotations:		openshift.io/image.dockerRepositoryCheck=2017-10-02T17:05:11Z
  Docker Pull Spec:	docker-registry.default.svc:5000/default/python
  Image Lookup:		local=false
  Unique Images:		1
  Tags:			2
  
  latest
    tagged from python@sha256:49c18358df82f4577386404991c51a9559f243e0b1bdc366df25
  
    * centos/python-35-centos7@sha256:49c18358df82f4577386404991c51a9559f243e0b1bdc366df25
        About a minute ago
  
  3.5
    tagged from centos/python-35-centos7
  
    * centos/python-35-centos7@sha256:49c18358df82f4577386404991c51a9559f243e0b1bdc366df25
        5 minutes ago

Procedure

• Add tags pointing to internal or external images, by using the oc tag command for all tag-related operations:

  $ oc tag <repository/image> <image-name:tag>

  For example, this command maps the docker.io/python:3.6.0 image to the 3.6 tag in the python image stream.

  $ oc tag docker.io/python:3.6.0 python:3.6

  Example output

  Tag python:3.6 set to docker.io/python:3.6.0.

  If the external image is secured, you must create a secret with credentials for accessing that registry.

Procedure

• Update a tag:

  $ oc tag <image-name:tag> <image-name:latest>

  For example, the following updates the latest tag to reflect the 3.6 tag in an image stream:

  $ oc tag python:3.6 python:latest

  Example output

  Tag python:latest set to python@sha256:438208801c4806548460b27bd1fbcb7bb188273d13871ab43f.

Procedure

• Remove old tags from an image stream:

  $ oc tag -d <image-name:tag>

  For example:

  $ oc tag -d python:3.6

  Example output

  Deleted tag default/python:3.6

Procedure

• Create an image stream that includes multi-architecture images, and sets the import mode to PreserveOriginal, by entering the following command:

  $ oc import-image <multiarch-image-stream-tag>  --from=<registry>/<project_name>/<image-name> \
  --import-mode='PreserveOriginal' --reference-policy=local --confirm

  Example output

  ---
  Arch:           <none>
  Manifests:      linux/amd64     sha256:6e325b86566fafd3c4683a05a219c30c421fbccbf8d87ab9d20d4ec1131c3451
                  linux/arm64     sha256:d8fad562ffa75b96212c4a6dc81faf327d67714ed85475bf642729703a2b5bf6
                  linux/ppc64le   sha256:7b7e25338e40d8bdeb1b28e37fef5e64f0afd412530b257f5b02b30851f416e1
  ---

• Alternatively, enter the following command to import an image with the Legacy import mode, which discards manifest lists and imports a single sub-manifest:

  $ oc import-image <multiarch-image-stream-tag>  --from=<registry>/<project_name>/<image-name> \
  --import-mode='Legacy' --confirm

  Note

  The --import-mode= default value is Legacy. Excluding this value, or failing to specify either Legacy or PreserveOriginal, imports a single sub-manifest. An invalid import mode returns the following error: error: valid ImportMode values are Legacy or PreserveOriginal.

• In some cases, users might want to use sub-manifests directly. When oc adm prune images is run, or the CronJob pruner runs, they cannot detect when a sub-manifest list is used. As a result, an administrator using oc adm prune images, or the CronJob pruner, might delete entire manifest lists, including sub-manifests.

  To avoid this limitation, you can use the manifest list by tag or by digest instead.

Procedure

• Run the following command to update your image stream from multi-architecture to single architecture by excluding the --import-mode= flag:

  $ oc import-image <multiarch-image-stream-tag> --from=<registry>/<project_name>/<image-name>

• Run the following command to update your image stream from single-architecture to multi-architecture:

  $ oc import-image <multiarch-image-stream-tag>  --from=<registry>/<project_name>/<image-name> \
  --import-mode='PreserveOriginal'