Transformation

Alter a request before matching and routing, such as with an Inja header template. You might transform the request or response to match a different routing destination based on the transformed content.

You can also apply special transformations, such as via Inja templates. With Inja, you can write loops, conditional logic, and other functions to transform requests and responses.

For more information, see the following resources.

• Gloo Mesh API docs
• The following video that shows how you might use transformation policies with other Gloo policies such as JWT and rate limiting.

Before you begin

1. Complete the multicluster getting started guide to set up the following testing environment.
   • Three clusters along with environment variables for the clusters and their Kubernetes contexts.
   • The Gloo Platform CLI, meshctl, along with other CLI tools such as kubectl and istioctl.
   • The Gloo management server in the management cluster, and the Gloo agents in the workload clusters.
   • Istio installed in the workload clusters.
   • A simple Gloo workspace setup.
2. Install Bookinfo and other sample apps.

Configure transformation policies

You can apply a transformation policy at the route level. For more information, see Apply policies.

Review the following sample configuration files.

apiVersion: trafficcontrol.policy.gloo.solo.io/v2
kind: TransformationPolicy
metadata:
  annotations:
    cluster.solo.io/cluster: ""
  name: basic-auth
  namespace: bookinfo
spec:
  applyToRoutes:
  - route:
      labels:
        route: ratings
  config:
    request:
      injaTemplate:
        headers:
          foo:
            text: bar

apiVersion: trafficcontrol.policy.gloo.solo.io/v2
kind: TransformationPolicy
metadata:
  annotations:
    cluster.solo.io/cluster: ""
  name: basic-auth
  namespace: bookinfo
spec:
  applyToRoutes:
  - route:
      labels:
        route: ratings
  config:
    response:
      injaTemplate:
        headers:
          foo:
            text: bar

apiVersion: trafficcontrol.policy.gloo.solo.io/v2
kind: TransformationPolicy
metadata:
  annotations:
    cluster.solo.io/cluster: ""
  name: transformation-one
  namespace: bookinfo
spec:
  applyToRoutes:
  - route:
      labels:
        route: ratings
  config:
    phase:
      postAuthz:
        priority: 10
    response:
      injaTemplate:
        advancedTemplates: false
        parseBodyBehavior: DontParse
        headers:
          baz:
            text: '{{ replace_with_random(header("baz"), "pattern-to-replace") }}'          
          foo:
            text: '{{ replace_with_random(header("x-foo"), "another-pattern-to-replace") }}'   
        body:
          text: ' {{ replace_with_random(body(), "pattern-to-replace") }}'

Verify transformation policies

1. Log in to the reviews app and send a request to the ratings app. Make sure that a 200 HTTP response code is returned.

   • Kubernetes 1.22 or earlier
   • Kubernetes 1.23 or later

   Create a temporary curl pod in the bookinfo namespace, so that you can test the app setup. You can also use this method in Kubernetes 1.23 or later, but an ephemeral container might be simpler, as shown in the other tab.

   1. Create the curl pod.

      kubectl run -it -n bookinfo curl \
        --image=curlimages/curl:7.73.0 --rm  -- sh
      

   2. Send a request to the ratings app.

      curl -v http://ratings:9080/ratings/1
      

      Example output:

      < HTTP/1.1 200 OK
      < content-type: application/json
      < date: Wed, 17 May 2023 14:45:24 GMT
      < x-envoy-upstream-service-time: 22
      < server: envoy
      < transfer-encoding: chunked
      Connection #0 to host ratings left intact
      {"id":1,"ratings":{"Reviewer1":5,"Reviewer2":4}}%  
      
      

   3. Exit the temporary pod. The pod deletes itself.

      exit
      

   Use the kubectl debug command to create an ephemeral curl container in the deployment. This way, the curl container inherits any permissions from the app that you want to test. If you don't run Kubernetes 1.23 or later, you can deploy a separate curl pod or manually add the curl container as shown in the other tab.

   kubectl --context ${REMOTE_CONTEXT1} -n bookinfo debug -i pods/$(kubectl get pod --context ${REMOTE_CONTEXT1} -l app=reviews -A -o jsonpath='{.items[0].metadata.name}') --image=curlimages/curl -- curl -v http://ratings:9080/ratings/1
   

   Example output:

   < HTTP/1.1 200 OK
   < content-type: application/json
   < date: Wed, 17 May 2023 14:45:24 GMT
   < x-envoy-upstream-service-time: 22
   < server: envoy
   < transfer-encoding: chunked
   Connection #0 to host ratings left intact
   {"id":1,"ratings":{"Reviewer1":5,"Reviewer2":4}}%  
   
   

2. Apply a transformation policy to the ratings app that adds the foo: bar response header.

   kubectl apply --context ${REMOTE_CONTEXT1} -f- <<EOF
   apiVersion: trafficcontrol.policy.gloo.solo.io/v2
   kind: TransformationPolicy
   metadata:
     annotations:
       cluster.solo.io/cluster: ""
     name: basic-auth
     namespace: bookinfo
   spec:
     applyToRoutes:
     - route:
         labels:
           route: ratings
     config:
       response:
         injaTemplate:
           headers:
             foo:
               text: bar
   EOF
   

3. Create a route table for the ratings app.

   kubectl apply --context ${REMOTE_CONTEXT1} -f- <<EOF
   apiVersion: networking.gloo.solo.io/v2
   kind: RouteTable
   metadata:
     name: ratings-rt
     namespace: bookinfo
   spec:
     hosts:
     - ratings
     http:
     - forwardTo:
         destinations:
         - ref:
             name: ratings
             namespace: bookinfo
             cluster: ${REMOTE_CLUSTER1}
       labels:
         route: ratings
     workloadSelectors:
     - {}
   EOF
   

4. Send another request to the ratings app by using the command in step 1. Verify that you now see the foo: bar header in your response.

   Example output:

      < HTTP/1.1 200 OK
      < content-type: application/json
      < date: Wed, 17 May 2023 16:48:51 GMT
      < x-envoy-upstream-service-time: 2
      < server: envoy
      < foo: bar
      < transfer-encoding: chunked
   
      * Connection #0 to host ratings left intact
      {"id":1,"ratings":{"Reviewer1":5,"Reviewer2":4}}% 
      

5. Optional: Clean up the resources that you created.

   kubectl -n bookinfo --context $REMOTE_CONTEXT1 delete transformationpolicy basic-auth
   kubectl -n bookinfo --context $REMOTE_CONTEXT1 delete routetable ratings-rt