Chapter 8. Triggering updates on image stream changes

OpenShift Container Platform 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.

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 OpenShift Container Platform to request triggering.

The annotation is defined as follows:

Key: image.openshift.io/triggers
Value:
[
 {
   "from": {
     "kind": "ImageStreamTag", 1
     "name": "example:latest", 2
     "namespace": "myapp", 3
   },
   "fieldPath": "spec.template.spec.containers[?(@.name='web')].image", 4
   "paused": "false" 5
 },
 ...
]

When one of the core Kubernetes resources contains both a pod template and this annotation, OpenShift Container Platform 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:

You can automatically trigger Kubernetes resources by updating the image stream tag.

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

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

You can manually trigger Kubernetes resources by entering the oc set triggers command.

When adding an image trigger to deployments, you can use the oc set triggers command. For example, the example 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.

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