Chapter 8. Triggering updates on image stream changes

Red Hat OpenShift Service on AWS classic architecture deployment configurations and build configurations can be automatically triggered by changes to image stream tags. The triggered action can be run using the new value of the image referenced by the updated image stream tag.

To enable Kubernetes resources, such as Deployments and StatefulSets, to seamlessly consume new image versions, configure image stream change triggers in Red Hat OpenShift Service on AWS classic architecture. This ensures your application deployments are automatically updated when the associated image stream detects a change.

Kubernetes resources do not have fields for triggering, unlike deployment and build configurations, which include as part of their API definition a set of fields for controlling triggers. Instead, you can use annotations in Red Hat OpenShift Service on AWS classic architecture to request triggering.

The annotation is defined as follows:

apiVersion: v1
kind: Pod
metadata:
  annotations:
    image.openshift.io/triggers:
      [
       {
         "from": {
           "kind": "ImageStreamTag",
           "name": "example:latest",
           "namespace": "myapp"
         },
         "fieldPath": "spec.template.spec.containers[?(@.name==\"web\")].image",
         "paused": false
       },
      # ...
      ]
# ...

apiVersion: v1
kind: Pod
metadata:
  annotations:
    image.openshift.io/triggers:
      [
       {
         "from": {
           "kind": "ImageStreamTag",
           "name": "example:latest",
           "namespace": "myapp"
         },
         "fieldPath": "spec.template.spec.containers[?(@.name==\"web\")].image",
         "paused": false
       },
      # ...
      ]
# ...

where:

When one of the core Kubernetes resources contains both a pod template and this annotation, Red Hat OpenShift Service on AWS classic architecture attempts to update the object by using the image currently associated with the image stream tag that is referenced by trigger. The update is performed against the fieldPath specified.

Examples of core Kubernetes resources that can contain both a pod template and annotation include:

To enable automatic updates for your deployed applications managed by Kubernetes, use the command-line interface (CLI) to set an image stream change trigger on Kubernetes resources. This ensures that resources, like Deployments and StatefulSets, are automatically invoked when a new version of an upstream image is available.

When adding an image trigger to deployments, you can use the oc set triggers command. For example, the sample command in this procedure adds an image change trigger to the deployment named example so that when the example:latest image stream tag is updated, the web container inside the deployment updates with the new image value. This command sets the correct image.openshift.io/triggers annotation on the deployment resource.