Tag Header Based Routing

Tag Header Based Routing

This sample explains the use of tag header based routing.

Tag Header Based Routing Feature

Tag header based routing allows users to send requests directly to specific tagged revisions with the same URL of Knative Service. To do this, you must set the specific header Knative-Serving-Tag: {revision-tag} in the request.

Currently Istio, Contour and Kourier ingress support this feature.

Prerequisites

A Knative cluster that has an ingress controller installed with Knative v0.16 and later.
Move into the docs directory:
```
cd $GOPATH/src/github.com/knative/docs
```

Enabling tag header based routing

This feature is disabled by default. To enable this feature, run the following command:

kubectl patch cm config-features -n knative-serving -p '{"data":{"tag-header-based-routing":"Enabled"}}'

Build images

Follow the instructions in helloworld-go to build the helloworld image and upload it to your container repository.

Replace {username} in the sample.yaml with your Docker Hub username.

Setting up the revisions with tag

In this sample, two Revisions are created. The first Revision is tagged with rev1. With this configuration, users can send requests directly to the first Revision using the URL of Knative Service plus the header Knative-Serving-Tag: rev1.

The Knative Service is configured to route all of the traffic to the second Revision, which means if users do not provide the Knative-Serving-Tag or they provide an incorrect value for Knative-Serving-Tag, the requests will be routed to the second Revision.

Run the following command to set up the Knative Service and Revisions.

kubectl apply -f docs/serving/samples/tag-header-based-routing/sample.yaml

Check the created resources

Check the two created Revisions using the following command

kubectl get revisions

You should see there are two Revisions: tag-header-revision-1 and tag-header-revision-2. It may take a few minutes for the Revisions to become ready.

Check the Knative Service using the following command

kubectl get ksvc tag-header -oyaml

You should see the following block which indicates the tag rev1 is successfully added to the first Revision.

  - revisionName: tag-header-revision-1
    percent: 0
    tag: rev1
  - revisionName: tag-header-revision-2
    percent: 100

Sending request with tag header

Run the following command to send a request to the first Revision.
```
curl ${INGRESS_IP} -H "Host:tag-header.default.example.com" -H "Knative-Serving-Tag:rev1"
```
where ${INGRESS_IP} is the IP of your ingress.

You should get the following response:
```
Hello First Revision!
```
Run the following command to send requests without the Knative-Serving-Tag header:
```
curl ${INGRESS_IP} -H "Host:tag-header.default.example.com"
```
You should get the response from the second Revision:
```
Hello Second Revision!
```
Run the following command to send requests with an incorrect Knative-Serving-Tag header:
```
curl ${INGRESS_IP} -H "Host:tag-header.default.example.com" -H "Knative-Serving-Tag:wrongHeader"
```
You should get the response from the second Revision:
```
Hello Second Revision!
```