Managing Images

You are viewing documentation for a release that is no longer supported. The latest supported version of version 3 is [3.11]. For the most recent version 4, see [4]

You are viewing documentation for a release that is no longer supported. The latest supported version of version 3 is [3.11]. For the most recent version 4, see [4]

Overview

An image stream comprises any number of container images identified by tags. It presents a single virtual view of related images, similar to a Docker image repository.

By watching an image stream, builds and deployments can receive notifications when new images are added or modified and react by performing a build or deployment, respectively.

There are many ways you can interact with images and set up image streams, depending on where the images’ registries are located, any authentication requirements around those registries, and how you want your builds and deployments to behave. The following sections cover a range of these topics.

Tagging Images

Before working with OKD image streams and their tags, it helps to first understand image tags in the context of container images generally.

Container images can have names added to them that make it more intuitive to determine what they contain, called a tag. Using a tag to specify the version of what is contained in the image is a common use case. If you have an image named ruby, you could have a tag named 2.0 for 2.0 version of Ruby, and another named latest to indicate literally the latest built image in that repository overall.

When interacting directly with images using the docker CLI, the docker tag command can add tags, which essentially adds an alias to an image that can consist of several parts. Those parts can include:

<registry_server>/<user_name>/<image_name>:<tag>

The <user_name> part in the above could also refer to a project or namespace if the image is being stored in an OKD environment with an internal registry (the OpenShift Container Registry).

OKD provides the oc tag command, which is similar to the docker tag command, but operates on image streams instead of directly on images.

Adding Tags to Image Streams

Keeping in mind that an image stream in OKD 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 image streams static-2.0 tag to always refer to the current image for the ruby image streams 2.0 tag:

$ oc tag ruby:2.0 ruby:static-2.0

This creates a new image stream tag named static-2.0 in the ruby image stream. The new tag directly references the image id that the ruby:2.0 image stream 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.

The --reference flag creates an image stream tag that is not imported. The tag points to the source location, permanently.

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 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.

Recommended Tagging Conventions

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.

Removing Tags from Image Streams

To remove a tag completely from an image stream run:

$ oc delete istag/ruby:latest

or:

$ oc tag -d ruby:latest

Referencing Images in Image Streams

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

• An **ImageStreamTag** is used to reference or retrieve an image for a given image stream and tag. It uses the following convention for its name:

  <image_stream_name>:<tag>

• An **ImageStreamImage** is used to reference or retrieve an image for a given image stream and image name. It uses the following convention for its name:

  <image_stream_name>@<id>

  The <id> is an immutable identifier for a specific image, also called a digest.

• A **DockerImage** is used to reference or retrieve an image for a given external registry. It uses standard Docker pull specification for its name, e.g.:

  openshift/ruby-20-centos7:2.0

  When no tag is specified, it is assumed the latest tag is used.

  You can also reference a third-party registry:

  registry.access.redhat.com/rhel7:latest

  Or an image with a digest:

  centos/ruby-22-centos7@sha256:3a335d7d8a452970c5b4054ad7118ff134b3a6b50a2bb6d0c07c746e8986b28e

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 OKD 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 get -o yaml --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:

Definition of an Image Object Retrieved via ImageStreamImage

$ oc get -o yaml --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

Using Image Streams with Kubernetes Resources

Image Streams, being OKD native resources, work out of the box with all the rest of native resources available in OKD, such as builds or deployments. Currently, it is also possible to make them work with native Kubernetes resources, such as jobs, replication controllers, replica sets or Kubernetes deployments.

The cluster administrator configures exactly what resources can be used.

When enabled, it is possible to put a reference to an image stream in the **image** field of a resource. When using this feature, it is only possible to reference image streams that reside in the same project as the resource. The image stream reference must consist of a single segment value, for example **ruby:2.5**, where **ruby** is the name of an image stream that has a tag named **2.5** and resides in the same project as the resource making the reference.

There are two ways to enable this:

1. Enabling image stream resolution on a specific resource. This allows only this resource to use the image stream name in the image field.

2. Enabling image stream resolution on an image stream. This allows all resources pointing to this image stream to use it in the image field.

Both of these operations can be done using oc set image-lookup. For example, the following command allows all resources to reference the image stream named mysql:

$ oc set image-lookup mysql

This sets the **Imagestream.spec.lookupPolicy.local** field to true.

Image stream with image lookup enabled

apiVersion: v1
kind: ImageStream
metadata:
  annotations:
    openshift.io/display-name: mysql
  name: mysql
  namespace: myproject
spec:
  lookupPolicy:
    local: true

When enabled, the behavior is enabled for all tags within the image stream.

You can query the image streams and see if the option is set using:

$ oc set image-lookup

You can also enable image lookup on a specific resource. This command allows the Kubernetes deployment named mysql to use image streams:

$ oc set image-lookup deploy/mysql

This sets the **alpha.image.policy.openshift.io/resolve-names** annotation on the deployment.

Deployment with image lookup enabled

apiVersion: apps/v1
kind: Deployment
metadata:
  name: mysql
  namespace: myproject
spec:
  replicas: 1
  template:
    metadata:
      annotations:
        alpha.image.policy.openshift.io/resolve-names: '*'
    spec:
      containers:
      - image: mysql:latest
        imagePullPolicy: Always
        name: mysql

To disable image lookup, pass **--enabled=false**:

$ oc set image-lookup deploy/mysql --enabled=false

Image Pull Policy

Each container in a pod has a container image. Once you have created an image and pushed it to a registry, you can then refer to it in the pod.

When OKD creates containers, it uses the container’s **imagePullPolicy** to determine if the image should be pulled prior to starting the container. There are three possible values for **imagePullPolicy**:

• **Always** - always pull the image.

• **IfNotPresent** - only pull the image if it does not already exist on the node.

• **Never** - never pull the image.

If a container’s **imagePullPolicy** parameter is not specified, OKD sets it based on the image’s tag:

1. If the tag is latest, OKD defaults **imagePullPolicy** to **Always**.

2. Otherwise, OKD defaults **imagePullPolicy** to **IfNotPresent**.

Accessing the Internal Registry

You can access OKD’s internal registry directly to push or pull images. For example, this could be helpful if you wanted to create an image stream by manually pushing an image, or just to docker pull an image directly.

The internal registry authenticates using the same tokens as the OKD API. To perform a docker login against the internal registry, you can choose any user name and email, but the password must be a valid OKD token.

To log into the internal registry:

1. Log in to OKD:

   $ oc login

2. Get your access token:

   $ oc whoami -t

3. Log in to the internal registry using the token. You must have docker installed on your system:

   $ docker login -u <user_name> -e <email_address> \
       -p <token_value> <registry_server>:<port>

   Contact your cluster administrator if you do not know the registry IP or host name and port to use.

In order to pull an image, the authenticated user must have get rights on the requested imagestreams/layers. In order to push an image, the authenticated user must have update rights on the requested imagestreams/layers.

By default, all service accounts in a project have rights to pull any image in the same project, and the builder service account has rights to push any image in the same project.

Using Image Pull Secrets

Docker registries can be secured to prevent unauthorized parties from accessing certain images. If you are using OKD’s internal registry and are pulling from image streams located in the same project, then your pod’s service account should already have the correct permissions and no additional action should be required.

However, for other scenarios, such as referencing images across OKD projects or from secured registries, then additional configuration steps are required. The following sections detail these scenarios and their required steps.

Allowing Pods to Reference Images Across Projects

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

Allowing Pods to Reference Images from Other Secured Registries

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 OKD’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 create secret generic <pull_secret_name> \
    --from-file=.dockercfg=<path/to/.dockercfg> \
    --type=kubernetes.io/dockercfg

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

$ oc create secret generic <pull_secret_name> \
    --from-file=.dockerconfigjson=<path/to/.docker/config.json> \
    --type=kubernetes.io/dockerconfigjson

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

$ oc create secret docker-registry <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>

Pulling from Private Registries with Delegated Authentication

A private registry can delegate authentication to a separate service. In these cases, image pull secrets must be defined for both the authentication and registry endpoints.

1. Create a secret for the delegated authentication server:

   $ oc create secret docker-registry \
       --docker-server=sso.redhat.com \
       --docker-username=developer@example.com \
       --docker-password=******** \
       --docker-email=unused \
       redhat-connect-sso
   secret/redhat-connect-sso

2. Create a secret for the private registry:

   $ oc create secret docker-registry \
       --docker-server=privateregistry.example.com \
       --docker-username=developer@example.com \
       --docker-password=******** \
       --docker-email=unused \
       private-registry
   secret/private-registry

$ docker login registry.connect.redhat.com —username developer@example.com
Password: *
Login Succeeded
$ oc create secret generic redhat-connect —from-file=.dockerconfigjson=.docker/config.json
$ oc secrets link default redhat-connect —for=pull

Importing Tag and Image Metadata

An image stream can be configured to import tag and image metadata from an image repository in an external Docker image registry. You can do this using a few different methods.

• You can manually import tag and image information with the oc import-image command using the --from option:

  $ oc import-image <image_stream_name>[:<tag>] --from=<docker_image_repo> --confirm

  For example:

  $ oc import-image my-ruby --from=docker.io/openshift/ruby-20-centos7 --confirm
  The import completed successfully.
  Name:            my-ruby
  Created:        Less than a second ago
  Labels:            <none>
  Annotations:        openshift.io/image.dockerRepositoryCheck=2016-05-06T20:59:30Z
  Docker Pull Spec:    172.30.94.234:5000/demo-project/my-ruby
  Tag    Spec                    Created            PullSpec                            Image
  latest    docker.io/openshift/ruby-20-centos7    Less than a second ago    docker.io/openshift/ruby-20-centos7@sha256:772c5bf9b2d1e8...    <same>

  You can also add the --all flag to import all tags for the image instead of just latest.

• Like most objects in OKD, you can also write and save a JSON or YAML definition to a file then create the object using the CLI. Set the **spec.dockerImageRepository** field to the Docker pull spec for the image:

  apiVersion: "v1"
  kind: "ImageStream"
  metadata:
    name: "my-ruby"
  spec:
    dockerImageRepository: "docker.io/openshift/ruby-20-centos7"

  Then create the object:

  $ oc create -f <file>

When you create an image stream that references an image in an external Docker registry, OKD communicates with the external registry within a short amount of time to get up to date information about the image.

After the tag and image metadata is synchronized, the image stream object would look similar to the following:

apiVersion: v1
kind: ImageStream
metadata:
  name: my-ruby
  namespace: demo-project
  selflink: /oapi/v1/namespaces/demo-project/imagestreams/my-ruby
  uid: 5b9bd745-13d2-11e6-9a86-0ada84b8265d
  resourceVersion: '4699413'
  generation: 2
  creationTimestamp: '2016-05-06T21:34:48Z'
  annotations:
    openshift.io/image.dockerRepositoryCheck: '2016-05-06T21:34:48Z'
spec:
  dockerImageRepository: docker.io/openshift/ruby-20-centos7
  tags:
    -
      name: latest
      annotations: null
      from:
        kind: DockerImage
        name: 'docker.io/openshift/ruby-20-centos7:latest'
      generation: 2
      importPolicy: {  }
status:
  dockerImageRepository: '172.30.94.234:5000/demo-project/my-ruby'
  tags:
    -
      tag: latest
      items:
        -
          created: '2016-05-06T21:34:48Z'
          dockerImageReference: 'docker.io/openshift/ruby-20-centos7@sha256:772c5bf9b2d1e8e80742ed75aab05820419dc4532fa6d7ad8a1efddda5493dc3'
          image: 'sha256:772c5bf9b2d1e8e80742ed75aab05820419dc4532fa6d7ad8a1efddda5493dc3'
          generation: 2

You can set a tag to query external registries at a scheduled interval to synchronize tag and image metadata by setting the --scheduled=true flag with the oc tag command as mentioned in Adding Tags to Image Streams.

Alternatively, you can set **importPolicy.scheduled** to true in the tag’s definition:

apiVersion: v1
kind: ImageStream
metadata:
  name: ruby
spec:
  tags:
  - from:
      kind: DockerImage
      name: openshift/ruby-20-centos7
    name: latest
    importPolicy:
      scheduled: true

Importing Images from Insecure Registries

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

Image Stream Tag Policies

Insecure Tag Import Policy

The above annotation applies to all images and tags of a particular ImageStream. For a finer-grained control, policies may be set on istags. Set importPolicy.insecure in the tag’s definition to true to allow a fall-back to insecure transport just for images under this tag.

Reference Policy

The Reference Policy allows you to specify from where resources that reference this image stream tag pulls the image. It applies to only images that you import from external registries. There are two options to choose from: Local and Source.

The Source policy instructs clients to pull directly from the source registry of the image. The integrated registry is not involved unless the image is managed by the cluster. (It is not an external image.) This is the default policy.

The Local policy instructs clients to always pull from the integrated registry. This is useful if you want to pull from external insecure registries without modifying Docker daemon settings.

This policy only affects the use of the image stream tag. Components or operations that directly reference or pull the image using its external registry location is not redirected to the internal registry.

The pull-through feature of the registry serves the remote image to the client. This feature, which is on by default, must be enabled for the local reference policy to be used. Additionally, by default, all the blobs are mirrored for faster access later.

You can set the policy in a specification of image stream tag as referencePolicy.type.

Example of Insecure Tag with a Local Reference Policy

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)

Importing Images from Private Registries

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, OKD picks up the secrets and provide them to the remote party.

Adding Trusted Certificates for External Registries

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).

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

Importing Images Across Projects

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:

1. First, add the necessary policy to access the other project:

   $ oc policy add-role-to-group \
       system:image-puller \
       system:serviceaccounts:<destination_project> \
       -n <source_project>

   This allows <destination_project> to pull images from <source_project>.

2. With the policy in place, you can import the image manually:

   $ oc import-image <new_image_stream> --confirm \
       --from=<docker_registry>/<source_project>/<image_stream>

Creating an Image Stream by Manually Pushing an Image

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

Before performing this procedure, the following must be satisfied:

• The destination project you push to must already exist.

• The user must be authorized to {get, update} "imagestream/layers" in that project. In addition, since the image stream does not already exist, the user must be authorized to {create} "imagestream" in that project. If you are a project administrator, then you would have these permissions.

To create an image stream by manually pushing an image:

1. First, log in to the internal registry.

2. Then, tag your image using the appropriate internal registry location. For example, if you had already pulled the docker.io/centos:centos7 image locally:

   $ docker tag docker.io/centos:centos7 https://registry.<clusterID>.openshift.com

3. Finally, push the image to your internal registry. For example:

   $ docker push https://registry.<clusterID>.openshift.com
   The push refers to a repository [https://registry.<clusterID>.openshift.com] (len: 1)
   c8a648134623: Pushed
   2bf4902415e3: Pushed
   latest: digest: sha256:be8bc4068b2f60cf274fc216e4caba6aa845fff5fa29139e6e7497bb57e48d67 size: 6273

4. Verify that the image stream was created:

$ oc get is
NAME       DOCKER REPO                        TAGS      UPDATED
my-image   172.30.48.125:5000/test/my-image   latest    3 seconds ago

Triggering Updates on Image Stream Changes

When an image stream tag is updated to point to a new image, OKD can automatically take action to roll the new image out to resources that were using the old image. This is configured in different ways depending on the type of resource that is referencing the image stream tag.

OpenShift Resources

OpenShift DeploymentConfigs and BuildConfigs can be automatically triggered by changes to ImageStreamTags. The triggered action can be run using the new value of the image referenced by the updated ImageStreamTag. For more details on using this capability see the documentation on BuildConfig triggers and DeploymentConfig triggers.

Kubernetes Resources

Unlike DeploymentConfigs and BuildConfigs, which include as part of their API definition a set of fields for controlling triggers, Kubernetes resources do not have fields for triggering. Instead, OKD uses annotations to allow users to request triggering. The annotation is defined as follows:

Key: image.openshift.io/triggers
Value: array of triggers, where each item has the schema:
[
 {
   "from" :{
     "kind": "ImageStreamTag", // required, the resource to trigger from, must be ImageStreamTag
     "name": "example:latest", // required, the name of an ImageStreamTag
     "namespace": "myapp",     // optional, defaults to the namespace of the object
   },
   // required, JSON path to change
   // Note that this field is limited today, and only accepts a very specific set
   // of inputs (a JSON path expression that precisely matches a container by ID or index).
   // For pods this would be "spec.containers[?(@.name='web')].image".
   "fieldPath": "spec.template.spec.containers[?(@.name='web')].image",
   // optional, set to true to temporarily disable this trigger.
   "paused": "false"
 },
 ...
]

When OKD sees one of the core Kubernetes resources that contains both a pod template (i.e, only CronJobs, Deployments, StatefulSets, DaemonSets, Jobs, ReplicaSets, ReplicationControllers, and Pods) and this annotation, it attempts to update the object using the image currently associated with the ImageStreamTag referenced by trigger. The update is performed against the fieldPath specified.

In the following example the trigger fires when the example:latest imagestream tag is updated. Upon firing, the object’s pod template image reference for the web container is updated with a new image value. If the pod template is part of a Deployment definition, the change to the pod template automatically triggers a deployment, effectively rolling out the new image.

image.openshift.io/triggers=[{"from":{"kind":"ImageStreamTag","name":"example:latest"},"fieldPath":"spec.template.spec.containers[?(@.name='web')].image"}]

When adding an Image Trigger to Deployments, you can also use the oc set triggers command. For example the following command adds an image change trigger to the Deployment named example such that when the example:latest image stream tag is updated, the web container inside the deployment updates with the new image value:

$ oc set triggers deploy/example --from-image=example:latest -c web

Unless the Deployment is paused, this pod template update automatically causes a deployment to occur with the new image value.

Writing Image Stream Definitions

You can define image streams by writing the image stream definition for the entire image stream. This allows you to distribute the definition to different clusters without running oc commands.

An image stream definition specifies information about the image stream and the specific tags to be imported.

Definition of an Image Stream Object

apiVersion: v1
kind: ImageStream
metadata:
  name: ruby
  annotations:
    openshift.io/display-name: Ruby (1)
spec:
  tags:
    - name: '2.0' (2)
      annotations:
        openshift.io/display-name: Ruby 2.0 (3)
        description: >- (4)
          Build and run Ruby 2.0 applications on CentOS 7. For more information
          about using this builder image, including OpenShift considerations,
          see
          https://github.com/sclorg/s2i-ruby-container/tree/master/2.0/README.md.
        iconClass: icon-ruby (5)
        sampleRepo: 'https://github.com/sclorg/ruby-ex.git' (6)
        tags: 'builder,ruby' (7)
        supports: 'ruby' (8)
        version: '2.0' (9)
      from:
        kind: DockerImage (10)
        name: 'docker.io/openshift/ruby-20-centos7:latest' (11)

For more information on the fields that can be defined in an ImageStream, see the Imagestream API and the ImagestreamTag API.