ch07s08 - Red Hat OpenShift Administration I: Operating a Production Cluster

Guided Exercise: Automatic Image Updates with OpenShift Image Change Triggers

Update an application that references container images indirectly though image streams.

Outcomes

Add an image trigger to a deployment.
Modify an image stream tag to point to a new image.
Watch the rollout of the application.
Roll back a deployment to the previous image.

As the student user on the workstation machine, use the lab command to prepare your system for this exercise.

This command ensures that all resources are available for this exercise. It also creates the updates-triggers project and deploys a web application with 10 replicas.

The command creates the /home/student/DO180/labs/updates-triggers/resources.txt file. The resources.txt file contains the name of the images and some commands that you use during the exercise. You can use the file to copy and paste these image names and commands.

[student@workstation ~]$ lab start updates-triggers

Instructions

Log in to the OpenShift cluster as the developer user with the developer password. Use the updates-triggers project.

[student@workstation ~]$ oc login -u developer -p developer \
  https://api.ocp4.example.com:6443
Login successful.
...output omitted...

Set the updates-triggers project as the active project.

[student@workstation ~]$ oc project updates-triggers
...output omitted...

Inspect the versioned-hello image stream that the lab command created.
1. Verify that the lab command enabled the local lookup policy for the versioned-hello image stream.
```
[student@workstation ~]$ oc set image-lookup
NAME             LOCAL
versioned-hello  true
```
2. Verify that the lab command created the versioned-hello:1 image stream tag. The image stream tag refers to the image in the classroom registry by its SHA ID.
  Note
  To improve readability, the instructions truncate the SHA-256 strings.
  On your system, the commands return the full SHA-256 strings. Also, you must type the full SHA-256 string, to provide such a parameter to a command.
```
[student@workstation ~]$ oc get istag
NAME               IMAGE REFERENCE ...
versioned-hello:1  ...:8443/redhattraining/versioned-hello@sha256:66e0...105e ...
```
3. Verify that the lab command created the versioned-hello:1 image stream tag from the registry.ocp4.example.com:8443/redhattraining/versioned-hello:1-123 image.
```
[student@workstation ~]$ oc get istag versioned-hello:1 \
  -o jsonpath='{.tag.from.name}{"\n"}'
registry.ocp4.example.com:8443/redhattraining/versioned-hello:1-123
```
Inspect the Deployment object that the lab command created. Verify that the application is available from outside the cluster.
1. List the Deployment objects. The version deployment retrieved the SHA image ID from the versioned-hello:1 image stream tag. The Deployment object includes a container named versioned-hello. You use that information in a later step, when you configure the trigger.
```
[student@workstation ~]$ oc get deployment -o wide
NAME     READY ... CONTAINERS        IMAGES ...
version  10/10 ... versioned-hello   .../versioned-hello@sha256:66e0...105e ...
```
2. Open a new terminal.
3. Run the /home/student/DO180/labs/updates-triggers/curl_loop.sh script that the lab command prepared. The script sends web requests to the application in a loop. Leave the script running and do not interrupt it.
```
[student@workstation ~]$ /home/student/DO180/labs/updates-triggers/curl_loop.sh
Hi!
Hi!
Hi!
Hi!
...output omitted...
```

Add an image trigger to the Deployment object.

Switch back to the first terminal window, and then use the oc set triggers command to add the trigger for the versioned-hello:1 image stream tag to the versioned-hello container.
```
[student@workstation ~]$ oc set triggers deployment/version \
  --from-image versioned-hello:1 --containers versioned-hello
deployment.apps/version triggers updated
```

Review the definition of the trigger from the image.openshift.io/triggers annotation.

[student@workstation ~]$ oc get deployment version \
  -o jsonpath='{.metadata.annotations.image\.openshift\.io/triggers}' | jq .
[
  {
    "from": {
      "kind": "ImageStreamTag",
      "name": "versioned-hello:1"
    },
    "fieldPath": "spec.template.spec.containers[?(@.name==\"versioned-hello\")].image"
  }
]

Update the versioned-hello:1 image stream tag to point to the 1-125 tag of the registry.ocp4.example.com:8443/redhattraining/versioned-hello image. Watch the output of the curl_loop.sh script to verify that the Deployment object automatically rolls out.
1. Use the oc tag command to update the versioned-hello:1 tag.
```
[student@workstation ~]$ oc tag \
  registry.ocp4.example.com:8443/redhattraining/versioned-hello:1-125 \
  versioned-hello:1
Tag versioned-hello:1 set to registry.ocp4.example.com:8443/redhattraining/versioned-hello:1-125.
```
2. Changing the image stream tag triggered a rolling update. Watch the output of the curl_loop.sh script in the second terminal.
  Before the update, only pods that use the earlier version of the image reply. During the rolling updates, both old and new pods respond. After the update, only pods that run the latest version of the image reply. The following output probably differs on your system.
```
...output omitted...
Hi!
Hi!
Hi!
Hi!
Hi! v1.1
Hi! v1.1
Hi!
Hi! v1.1
Hi!
Hi! v1.1
Hi! v1.1
Hi! v1.1
Hi! v1.1
...output omitted...
```
  Do not stop the script.

Inspect the Deployment object and the image stream.

List the version deployment and notice that the image changed.

[student@workstation ~]$ oc get deployment version -o wide
NAME     READY ... CONTAINERS        IMAGES ...
version  10/10 ... versioned-hello   .../versioned-hello@sha256:834d...fcb4 ...

Display the details of the versioned-hello image stream. The versioned-hello:1 image stream tag points to the image with the same SHA ID as in the Deployment object.

Notice that the preceding image is still available. In the following step, you roll back to that image by specifying its SHA ID.

[student@workstation ~]$ oc describe is versioned-hello
Name:           versioned-hello
Namespace:      updates-triggers
...output omitted...

1
  tagged from registry.ocp4.example.com:8443/redhattraining/versioned-hello:1-125

  * registry.ocp4.example.com:8443/.../versioned-hello@sha256:834d...fcb4
      6 minutes ago
    registry.ocp4.example.com:8443/.../versioned-hello@sha256:66e0...105e
      37 minutes ago

Roll back the Deployment object by reverting the versioned-hello:1 image stream tag.
1. Use the oc tag command. For the source image, copy and paste the old image name and the SHA ID from the output of the preceding command.
```
[student@workstation ~]$ oc tag \
registry.ocp4.example.com:8443/redhattraining/versioned-hello@sha256:66e0...105e \
versioned-hello:1
Tag versioned-hello:1 set to registry.ocp4.example.com:8443/redhattraining/versioned-hello@sha256:66e0...105e.
```
2. Watch the output of the curl_loop.sh script in the second terminal. The pods that run the v1.0 version of the application are responding again. The following output probably differs on your system.
```
...output omitted...
Hi! v1.1
Hi! v1.1
Hi! v1.1
Hi! v1.1
Hi!
Hi! v1.1
Hi! v1.1
Hi! v1.1
Hi!
Hi! v1.1
Hi! v1.1
Hi!
Hi!
Hi!
...output omitted...
```
  Press Ctrl+C to quit the script. Close that second terminal when done.

Finish

On the workstation machine, use the lab command to complete this exercise. This step is important to ensure that resources from previous exercises do not impact upcoming exercises.

[student@workstation ~]$ lab finish updates-triggers

Guided Exercise: Automatic Image Updates with OpenShift Image Change Triggers

Note