Openshift ImageStreams quickstart
ImageStreams are a feature in OpenShift that offer virtual Docker images.
An ImageStream virtual image points to actual Docker images located in other registries. During deployment, ImageStreams act as proxies, supplying the real images.
Utilizing ImageStreams is useful when changing the image of a deployment: Instead of altering the deployment template, you can simply update the ImageStream tag.
Moreover, you can configure triggers to automatically initiate rollouts when an ImageStream tag changes.
In this post I explain the basic commands for managing Openshift ImageStreams and how to configure ImageStreams in deployments.
Create an ImageStream
ImageStreams are stored in namespaces. First, select the namespace where you want to create it: oc project [NAMESPACE_NAME]
After, run this to create the ImageStream: oc create imagestream [NAME]
Execute oc describe imagestream [NAME] to see the properties of the ImageStream, including the repository of the virtual image.
Example:
PS C:\examples> oc create imagestream is-example
imagestream.image.openshift.io/is-example created
PS C:\examples> oc describe imagestream is-example
Name: is-example
Namespace: examples
Created: 11 seconds ago
Labels: <none>
Annotations: <none>
Image Repository: default-route-openshift-image-registry.apps-crc.testing/examples/is-example
Image Lookup: local=false
Tags: <none>
PS C:\examples>
Create or update ImageStream tags
Use the command oc tag [REMOTE_IMAGE]:[TAG] [IMAGESTREAM_NAME]:[TAG] to create or change the tags of the image stream.
Example:
PS C:\examples> oc tag us-docker.pkg.dev/google-samples/containers/gke/hello-app:1.0 is-example:prod
Tag is-example:prod set to us-docker.pkg.dev/google-samples/containers/gke/hello-app:1.0.
PS C:\examples> oc tag us-docker.pkg.dev/google-samples/containers/gke/hello-app:2.0 is-example:prod
Tag is-example:prod set to us-docker.pkg.dev/google-samples/containers/gke/hello-app:2.0.
PS C:\examples>
Each ImageStream has a history of changes which provides useful information for debugging purposes. Run the oc describe imagestream [IMAGESTREAM_NAME] command to see it.
PS C:\examples> oc describe imagestream is-example
Name: is-example
Namespace: examples
Created: 14 minutes ago
Labels: <none>
Annotations: openshift.io/image.dockerRepositoryCheck=2023-08-20T18:15:06Z
Image Repository: default-route-openshift-image-registry.apps-crc.testing/examples/is-example
Image Lookup: local=false
Unique Images: 2
Tags: 1
prod
tagged from us-docker.pkg.dev/google-samples/containers/gke/hello-app:2.0
* us-docker.pkg.dev/google-samples/containers/gke/hello-app@sha256:c4b0d869bd22cb3d1207848b385c389f7a4ab7a481184476ee7b98e7876ee594
24 seconds ago
us-docker.pkg.dev/google-samples/containers/gke/hello-app@sha256:845f77fab71033404f4cfceaa1ddb27b70c3551ceb22a5e7f4498cdda6c9daea
About a minute ago
PS C:\examples>
Add ImageStreams to deployment templates
To use ImageStreams in deployments just put the image repository and the desired tag in the value of the property image
Example:
apiVersion: apps.openshift.io/v1
kind: DeploymentConfig
metadata:
name: is-example-deployment
spec:
selector:
app: is-example
replicas: 1
template:
metadata:
labels:
app: is-example
spec:
containers:
- name: is-example
image: default-route-openshift-image-registry.apps-crc.testing/examples/is-example:prod
ports:
- containerPort: 8080
livenessProbe:
httpGet:
path: /
port: 8080
initialDelaySeconds: 3
periodSeconds: 3
Trigger rollout when ImageStream changes
To run a rollout automatically when an ImageStream tag changes add an ImageChange trigger with the reference to the ImageStreams image, tag, and the containers that you want to rollout.
apiVersion: apps.openshift.io/v1
kind: DeploymentConfig
metadata:
name: is-example-deployment
spec:
selector:
app: is-example
replicas: 1
template:
metadata:
labels:
app: is-example
spec:
containers:
- name: is-example
image: default-route-openshift-image-registry.apps-crc.testing/examples/is-example:prod
ports:
- containerPort: 8080
livenessProbe:
httpGet:
path: /
port: 8080
initialDelaySeconds: 3
periodSeconds: 3
triggers:
- type: ImageChange
imageChangeParams:
automatic: true
containerNames:
- is-example
from:
kind: ImageStreamTag
name: 'is-example:prod'
namespace: examples
Example:
PS C:\examples> oc get pods
NAME READY STATUS RESTARTS AGE
is-example-deployment-3-l4xk9 1/1 Running 0 68s
PS C:\examples> oc tag us-docker.pkg.dev/google-samples/containers/gke/hello-app:1.0 is-example:prod
Tag is-example:prod set to us-docker.pkg.dev/google-samples/containers/gke/hello-app:1.0.
PS C:\examples> oc get pods
NAME READY STATUS RESTARTS AGE
is-example-deployment-4-d6ql2 1/1 Running 0 8s
is-example-deployment-4-deploy 0/1 Completed 0 10s
PS C:\examples>
