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Change Configuration

In Knative Serving whenever you change Configuration of the Service, it creates a new Revision which is a point-in-time snapshot of code. It also creates a new Route and the new Revision will start receiving traffic.

Diagram

Change environment variable

To see how Knative reacts to configuration changes, let's change the environment variable the container reads.

Create a service-v2.yaml file that changes TARGET value to v2.

Note that the image is still pointing to v1 version. Apply the change:

kubectl apply -f service-v2.yaml

Now, you should see a new pod and a revision is created for the configuration change:

kubectl get pod,configuration,revision,route

NAME                                                      READY     STATUS    RESTARTS
pod/helloworld-c4pmt-deployment-7fdb5c5dc9-p2hr6   3/3       Running   0
pod/helloworld-vkvjt-deployment-7d7d9c9fdd-r27v8   3/3       Running   0

NAME                                                  configuration.serving.knative.dev/helloworld

NAME
revision.serving.knative.dev/helloworld-c4pmt
revision.serving.knative.dev/helloworld-vkvjt

NAME
route.serving.knative.dev/helloworld

Test that the route is also updated and prints out v2:

curl http://helloworld.default.$ISTIO_INGRESS.xip.io

Hello v2

Change container image

Configuration changes are not limited to environment variables. For example, a new container image would also trigger a new revision and traffic routed to that revision.

To see this in action, change your main file to say 'Bye' instead of 'Hello':

  • C# Startup.cs

    await context.Response.WriteAsync($"Bye {target}\n");

  • Python app.py

    return f'Bye {target}\n'

Build and push the Docker image tagging with v3. Replace {username} with your actual Docker Hub username:

docker build -t {username}/helloworld:v3 .

docker push {username}/helloworld:v3

Once the container image is pushed, create a service-v3.yaml file that changes TARGET value to v3 but more importantly, it refers to the new image with tag v3.

Apply the change:

kubectl apply -f service-v3.yaml

Test that the route is updated to v3 with the new container. It prints not only v3 (from env variable) but also says Bye (from container):

curl http://helloworld.default.$ISTIO_INGRESS.xip.io
Bye v3