Basics of Traffic Splitting

    What are some common traffic splitting use-cases?

    Splitting traffic is useful for a number of very common modern infrastructure needs, such as blue/green deployments and . Bringing these industry standards to bear on Kubernetes is as simple as a single CLI command on Knative or YAML tweak, let’s see how!

    A new Revision gets created each and every time you make changes to the configuration of your Knative Service. When splitting traffic, Knative splits traffic between different Revisions of your Knative Service.

    What exactly is a Revision?

    You can think of a Revision snapshot-in-time of application code and configuration.

    Instead of update the environment variable TARGET on your Knative Service hello to greet “Knative” instead.

    knYAML

    Deploy the updated version of your Knative Service by running the command:

    As before, kn prints out some helpful information to the CLI.

    Expected output

    1. Service 'hello' created to latest revision 'hello-00002' is available at URL:
    2. http://hello.default.${LOADBALANCER_IP}.sslip.io

    1. Edit your existing hello.yaml file to contain the following:

      1. ---
      2. apiVersion: serving.knative.dev/v1
      3. kind: Service
      4. metadata:
      5.   name: hello
      6. spec:
      7.   template:
      8.       containers:
      9.         - image: gcr.io/knative-samples/helloworld-go
      10.           ports:
      11.             - containerPort: 8080
      12.           env:
      13.             - name: TARGET
      1. kubectl apply -f hello.yaml

      Expected output

      1. service.serving.knative.dev/hello configured

    Note that since we are updating an existing Knative Service hello, the URL doesn’t change, but our new Revision should have the new name hello-00002.

    To see the change, access the Knative Service again on your browser or use curl in your terminal:

    1. echo "Accessing URL $(kn service describe hello -o url)"
    2. curl "$(kn service describe hello -o url)"

    Expected output

    Splitting Traffic

    You may at this point be wondering, “where did ‘Hello World!’ go?” Remember, Revisions are an immutable snapshot-in-time of application code and configuration, so your old hello-00001 Revision is still available to you.

    We can easily see a list of our existing Revisions with the kn or kubectl CLI.

    knkubectl

    View a list of revisions by running the command:

    1. kn revisions list

    Expected output

    1. NAME            SERVICE   TRAFFIC   TAGS   GENERATION   AGE   CONDITIONS   READY   REASON
    2. hello-00002     hello     100%             2            30s   3 OK / 4     True
    3. hello-00001     hello                      1            5m    3 OK / 4     True

    View a list of Revisions by running the command:

    1. kubectl get revisions

    Expected output

    1. hello-00001   hello                            1            True             0                 0
    2. hello-00002   hello                            2            True             0                 0

    When you create a new Revision of a Knative Service, Knative defaults to directing 100% of traffic to this latest Revision. We can change this default behavior by specifying how much traffic we want each of our Revisions to receive.

    Lets split traffic between our two Revisions:

    knYAML

    Run the command:

    1. kn service update hello \
    2. --traffic hello-00001=50 \
    3. --traffic @latest=50

    1. Add the traffic section to the bottom of your existing hello.yaml file:

    2. Apply the YAML by running the command:

      1. kubectl apply -f hello.yaml

    Info

    @latest will always point to our “latest” Revision which, at the moment, is hello-00002.

    To verify that the traffic split has configured correctly, list the revisions again by running the command:

    1. kn revisions list

    Expected output

    1. NAME            SERVICE   TRAFFIC   TAGS   GENERATION   AGE   CONDITIONS   READY   REASON
    2. hello-00002     hello     50%              2            10m   3 OK / 4     True
    3. hello-00001     hello     50%              1            36m   3 OK / 4     True

    Access your Knative Service multiple times in your browser to see the different output being served by each Revision.

    1. echo "Accessing URL $(kn service describe hello -o url)"
    2. curl "$(kn service describe hello -o url)"

    Expected output

    1. Hello Knative!
    2. Hello World!
    3. Hello Knative!