The following example walks you through how to use an Inja template to extract a value from a request header and to add this value as a header to your responses.

Before you begin

  1. Follow the Get started guide to install Gloo Gateway, set up a gateway resource, and deploy the httpbin sample app.

  2. Get the external address of the gateway and save it in an environment variable.

      export INGRESS_GW_ADDRESS=$(kubectl get svc -n gloo-system gloo-proxy-http -o jsonpath='{.status.loadBalancer.ingress[0].ip}')
echo $INGRESS_GW_ADDRESS  
  
      export INGRESS_GW_ADDRESS=$(kubectl get svc -n gloo-system gloo-proxy-http -o jsonpath='{.status.loadBalancer.ingress[0].hostname}')
echo $INGRESS_GW_ADDRESS
  
      kubectl port-forward deployment/gloo-proxy-http -n gloo-system 8080:8080

Inject response headers

  1. Create a VirtualHostOption resource with your transformation rules. In the following example, you use the value from the x-solo-request request header and populate the value of that header into an x-solo-response response header.

      kubectl apply -n gloo-system -f- <<EOF
apiVersion: gateway.solo.io/v1
kind: VirtualHostOption
metadata:
  name: transformation
  namespace: gloo-system
spec:
  options:
    transformations:
      responseTransformation:
        transformationTemplate:
          headers:
            x-solo-response:
              text: '{{ request_header("x-solo-request") }}'
  targetRefs:
  - group: gateway.networking.k8s.io
    kind: Gateway
    name: http
    namespace: gloo-system
EOF

  2. Send a request to the httpbin app and include the x-solo-request request header. Verify that you get back a 200 HTTP response code and that the value of the x-solo-request header was added to the x-solo-response response header.

      curl -vik http://$INGRESS_GW_ADDRESS:8080/response-headers \
 -H "host: www.example.com:8080" \
 -H "x-solo-request: my custom request header" 
  
      curl -vik localhost:8080/response-headers \
-H "host: www.example.com" \
-H "x-solo-request: my custom request header"

    Example output:

       * Mark bundle as not supporting multiuse
   < HTTP/1.1 200 OK
   HTTP/1.1 200 OK
   < access-control-allow-credentials: true
   access-control-allow-credentials: true
   < access-control-allow-origin: *
   access-control-allow-origin: *
   < content-type: application/json; encoding=utf-8
   content-type: application/json; encoding=utf-8
   < date: Wed, 26 Jun 2024 02:54:48 GMT
   date: Wed, 26 Jun 2024 02:54:48 GMT
   < content-length: 3
   content-length: 3
   < x-envoy-upstream-service-time: 2
   x-envoy-upstream-service-time: 2
   < server: envoy
   server: envoy
   < x-envoy-decorator-operation: httpbin.httpbin.svc.cluster.local:8000/*
   x-envoy-decorator-operation: httpbin.httpbin.svc.cluster.local:8000/*
   < x-solo-response: my custom request header
   x-solo-response: my custom request header

Cleanup

You can remove the resources that you created in this guide.

  kubectl delete virtualhostoption transformation -n gloo-system