Traffic splitting¶

Starting state: You have completed Autoscaling, and hello still returns Hello World!. Stay in the same cluster and default namespace.

You will create a second Revision, then route half the traffic to each Revision. A Revision is a snapshot of a Service's application code and configuration. Traffic splitting can support blue/green deployments and canary deployments.

Creating a new Revision¶

Before updating the Service, save the name of the current Revision. This avoids assuming a generated name such as hello-00001.

ORIGINAL_REVISION=$(kubectl get ksvc hello -o jsonpath='{.status.latestReadyRevisionName}')
printf 'Original Revision: %s\n' "$ORIGINAL_REVISION"
kn service update hello --env TARGET=Knative

Run the following commands in this same terminal so that ORIGINAL_REVISION remains available.

Expected result

The update completes and reports a new Revision. The Service URL stays the same.

Accessing the new Revision¶

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

Expected output

Hello Knative!

View existing Revisions¶

kn revision list

Find the two Revisions for hello. The TRAFFIC column shows that the new Revision receives 100% of traffic and the original receives none. In this exercise, no traffic configuration was specified before the update, so traffic follows the latest Revision.

Splitting traffic between Revisions¶

kn service update hello \
  --traffic "$ORIGINAL_REVISION=50" \
  --traffic @latest=50

@latest points to the latest Revision, which in this exercise is the one greeting Knative.

YAML equivalent (not needed for this route)

See update hello and split traffic for the declarative form. Continue using the CLI in this lesson.

Verify the traffic split¶

kn revision list

Expected result

Both Revisions for hello show 50% in the TRAFFIC column.

Send several requests:

SERVICE_URL=$(kn service describe hello -o url)
for i in $(seq 1 10); do
  curl "$SERVICE_URL"
done

You should see both Hello World! and Hello Knative!. A 50/50 configuration does not promise strict alternation or exactly five responses of each kind in ten requests. The Revision listing verifies the configured split.

You have deployed, scaled, and updated a Service. Next, use another Service to send and receive events.

Previous: Observe autoscaling · Next: Try Eventing