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Routing and managing traffic with blue/green deployment

This sample demonstrates updating an application to a new version using a blue/green traffic routing pattern. With Knative, you can safely reroute traffic from a live version of an application to a new version by changing the routing configuration.

Before you begin

You need:

Deploying Revision 1 (Blue)

We'll be deploying an image of a sample application that displays the text "App v1" on a blue background.

First, create a new file called blue-green-demo-config.yamland copy this into it:

apiVersion: serving.knative.dev/v1alpha1
kind: Configuration
metadata:
  name: blue-green-demo
  namespace: default
spec:
  revisionTemplate:
    metadata:
      labels:
        knative.dev/type: container
    spec:
      container:
        image: gcr.io/knative-samples/knative-route-demo:blue # The URL to the sample app docker image
        imagePullPolicy: Always
        env:
          - name: T_VERSION
            value: "blue"

Save the file, then deploy the configuration to your cluster:

kubectl apply -f blue-green-demo-config.yaml

configuration "blue-green-demo" configured

This will deploy the initial revision (blue-green-demo-00001) of the sample application. To route inbound traffic to it, we'll define a route. Create a new file called blue-green-demo-route.yaml and copy this into it:

apiVersion: serving.knative.dev/v1alpha1
kind: Route
metadata:
  name: blue-green-demo # The name of our route; appears in the URL to access the app
  namespace: default # The namespace we're working in; also appears in the URL to access the app
spec:
  traffic:
  - revisionName: blue-green-demo-00001
    percent: 100 # All traffic goes to this revision

Save the file, then apply the route to your cluster:

kubectl apply -f blue-green-demo-route.yaml

route "blue-green-demo" configured

You'll now be able to view the sample app at http://blue-green-demo.default.YOUR_CUSTOM_DOMAIN.com (replace YOUR_CUSTOM_DOMAIN) with the custom domain you configured for use with Knative.

Note: If you don't have a custom domain configured for use with Knative, you can interact with your app using cURL requests if you have the host URL and IP address: curl -H "Host: blue-green-demo.default.example.com" http://IP_ADDRESS
Knative creates the host URL by combining the name of your Route object, the namespace, and example.com, if you haven't configured a custom domain. For example, [route-name].[namespace].example.com. You can get the IP address by entering kubectl get svc knative-ingressgateway -n istio-system and copying the EXTERNAL-IP returned by that command. See Interacting with your app for more information.

Deploying Revision 2 (Green)

Revision 2 of the sample application will display the text "App v2" on a green background. To create the new revision, we'll edit our existing configuration in blue-green-demo-config.yaml with an updated image and environment variables:

apiVersion: serving.knative.dev/v1alpha1
kind: Configuration
metadata:
  name: blue-green-demo # Configuration name is unchanged, since we're updating an existing Configuration
  namespace: default
spec:
  revisionTemplate:
    metadata:
      labels:
        knative.dev/type: container
    spec:
      container:
        image: gcr.io/knative-samples/knative-route-demo:green # URL to the new version of the sample app docker image
        imagePullPolicy: Always
        env:
          - name: T_VERSION
            value: "green" # Updated value for the T_VERSION environment variable

Save the file, then apply the updated configuration to your cluster:

kubectl apply -f blue-green-demo-config.yaml

configuration "blue-green-demo" configured

At this point, the first revision (blue-green-demo-00001) and the second revision (blue-green-demo-00002) will both be deployed and running. We can update our existing route to create a new (test) endpoint for the second revision while still sending all other traffic to the first revision. Edit blue-green-demo-route.yaml:

apiVersion: serving.knative.dev/v1alpha1
kind: Route
metadata:
  name: blue-green-demo # Route name is unchanged, since we're updating an existing Route
  namespace: default
spec:
  traffic:
  - revisionName: blue-green-demo-00001
    percent: 100 # All traffic still going to the first revision
  - revisionName: blue-green-demo-00002
    percent: 0 # 0% of traffic routed to the second revision
    name: v2 # A named route

Save the file, then apply the updated route to your cluster:

kubectl apply -f blue-green-demo-route.yaml

route "blue-green-demo" configured

Revision 2 of the app is staged at this point. That means:

  • No traffic will be routed to revision 2 at the main URL, http://blue-green-demo.default.YOUR_CUSTOM_DOMAIN.com
  • Knative creates a new route named v2 for testing the newly deployed version at http://v2.blue-green-demo.default.YOUR_CUSTOM_DOMAIN.com

This allows you to validate that the new version of the app is behaving as expected before switching any traffic over to it.

Migrating traffic to the new revision

We'll once again update our existing route to begin shifting traffic away from the first revision and toward the second. Edit blue-green-demo-route.yaml:

apiVersion: serving.knative.dev/v1alpha1
kind: Route
metadata:
  name: blue-green-demo # Updating our existing route
  namespace: default
spec:
  traffic:
  - revisionName: blue-green-demo-00001
    percent: 50 # Updating the percentage from 100 to 50
  - revisionName: blue-green-demo-00002
    percent: 50 # Updating the percentage from 0 to 50
    name: v2

Save the file, then apply the updated route to your cluster:

kubectl apply -f blue-green-demo-route.yaml

route "blue-green-demo" configured

Refresh the original route (http://blue-green-demo.default.YOUR_CUSTOM_DOMAIN.com) a few times to see that some traffic now goes to version 2 of the app.

Note: This sample shows a 50/50 split to assure you don't have to refresh too much, but it's recommended to start with 1-2% of traffic in a production environment

Rerouting all traffic to the new version

Lastly, we'll update our existing route to finally shift all traffic to the second revision. Edit blue-green-demo-route.yaml:

apiVersion: serving.knative.dev/v1alpha1
kind: Route
metadata:
  name: blue-green-demo # Updating our existing route
  namespace: default
spec:
  traffic:
  - revisionName: blue-green-demo-00001
    percent: 0
    name: v1 # Adding a new named route for v1
  - revisionName: blue-green-demo-00002
    percent: 100
    # Named route for v2 has been removed, since we don't need it anymore

Save the file, then apply the updated route to your cluster:

kubectl apply -f blue-green-demo-route.yaml

route "blue-green-demo" configured

Refresh the original route (http://blue-green-demo.default.YOUR_CUSTOM_DOMAIN.com) a few times to verify that no traffic is being routed to v1 of the app.

We added a named route to v1 of the app, so you can now access it at http://v1.blue-green-demo.default.YOUR_CUSTOM_DOMAIN.com.

With all inbound traffic being directed to the second revision of the application, Knative will soon scale the first revision down to 0 running pods and the blue/green deployment can be considered complete. Using the named v1 route will reactivate a pod to serve any occassional requests intended specifically for the initial revision.

Cleaning up

To delete the sample app, enter the following commands:

kubectl delete route blue-green-demo
kubectl delete configuration blue-green-demo