Chapter 8. Triggering updates on image stream changes
When an image stream tag is updated to point to a new image, Red Hat OpenShift Service on AWS can automatically take action to roll the new image out to resources that were using the old image. You configure this behavior in different ways depending on the type of resource that references the image stream tag.
8.1. Red Hat OpenShift Service on AWS resources
Red Hat OpenShift Service on AWS 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.
8.2. Triggering Kubernetes resources
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 to request triggering.
The annotation is defined as follows:
apiVersion: v1
kind: Pod
metadata:
annotations:
image.openshift.io/triggers:
[
{
"from": {
"kind": "ImageStreamTag", 1
"name": "example:latest", 2
"namespace": "myapp" 3
},
"fieldPath": "spec.template.spec.containers[?(@.name==\"web\")].image", 4
"paused": false 5
},
# ...
]
# ...- 1
- Required:
kindis the resource to trigger from must beImageStreamTag. - 2
- Required:
namemust be the name of an image stream tag. - 3
- Optional:
namespacedefaults to the namespace of the object. - 4
- Required:
fieldPathis the JSON path to change. This field is limited and accepts only a JSON path expression that precisely matches a container by ID or index. For pods, the JSON path isspec.containers[?(@.name='web')].image. - 5
- Optional:
pausedis whether or not the trigger is paused, and the default value isfalse. Setpausedtotrueto temporarily disable this trigger.
When one of the core Kubernetes resources contains both a pod template and this annotation, Red Hat OpenShift Service on AWS 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:
-
CronJobs -
Deployments -
StatefulSets -
DaemonSets -
Jobs -
ReplicationControllers -
Pods
8.3. Setting the image trigger on Kubernetes resources
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.
Procedure
Trigger Kubernetes resources by entering the
oc set triggerscommand:$ oc set triggers deploy/example --from-image=example:latest -c web
Example deployment with trigger annotation
apiVersion: apps/v1 kind: Deployment metadata: annotations: image.openshift.io/triggers: '[{"from":{"kind":"ImageStreamTag","name":"example:latest"},"fieldPath":"spec.template.spec.containers[?(@.name==\"container\")].image"}]' # ...Unless the deployment is paused, this pod template update automatically causes a deployment to occur with the new image value.
