Traffic splitting¶

Traffic splitting is useful for blue/green deployments and canary deployments.

A Revision is a snapshot-in-time of application code and configuration. A new Revision is created every time you make changes to the configuration of a Knative Service. When splitting traffic, Knative splits traffic between different Revisions of your Knative Service.

Creating a new Revision¶

Instead of TARGET=World, update the environment variable TARGET on your Knative Service to greet "Knative" instead.

knYAML

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

kn service update hello \
--env TARGET=Knative

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

Expected output

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

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

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: hello
spec:
  template:
    spec:
      containers:
        - image: ghcr.io/knative/helloworld-go:latest
          ports:
            - containerPort: 8080
          env:
            - name: TARGET
              value: "Knative"

Deploy the updated version of your Knative Service by running the command:
```
kubectl apply -f hello.yaml
```
Expected output
```
service.serving.knative.dev/hello configured
```

Because you are updating an existing Knative Service, the URL won't change, but the new Revision has the new name hello-00002.

Accessing the new Revision¶

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

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

Expected output

Hello Knative!

View existing Revisions¶

You can view a list of existing Revisions by using the Knative (kn) or kubectl CLI:

knkubectl

View a list of revisions by running the command:

kn revisions list

Expected output

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

View a list of Revisions by running the command:

kubectl get revisions

Expected output

NAME          CONFIG NAME   K8S SERVICE NAME   GENERATION   READY   REASON   ACTUAL REPLICAS   DESIRED REPLICAS
hello-00001   hello                            1            True             0                 0
hello-00002   hello                            2            True             0                 0

When running the kn command, the relevant column is TRAFFIC. You can see that 100% of traffic is going to the latest Revision, hello-00002, which is on the row with the highest GENERATION. 0% of traffic is going to the Revision hello-00001.

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

Splitting traffic between Revisions¶

Split the traffic between the two Revisions:

knYAML

Run the command:

kn service update hello \
--traffic hello-00001=50 \
--traffic @latest=50

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

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: hello
spec:
  template:
    spec:
      containers:
        - image: ghcr.io/knative/helloworld-go:latest
          ports:
            - containerPort: 8080
          env:
            - name: TARGET
              value: "Knative"
  traffic:
  - latestRevision: true
    percent: 50
  - latestRevision: false
    percent: 50
    revisionName: hello-00001

Apply the YAML by running the command:
```
kubectl apply -f hello.yaml
```

Info

@latest always points to the "latest" Revision, which in this case is hello-00002.

Verify the traffic split¶

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

kn revisions list

Expected output

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

Similarly, you can access the Service URL from the terminal multiple times to see the traffic being split between the Revisions.

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

Expected output

Hello Knative!
Hello World!
Hello Knative!
Hello World!