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Traffic management
Transformations
Update request paths and methods

Update request paths and methods

To update the path and HTTP method the :path and :method pseudo headers are used.

Before you begin

  1. Follow the Get started guide to install kgateway.

  2. Follow the Sample app guide to create an API gateway proxy with an HTTP listener and deploy the httpbin sample app.

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

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

Update request paths and HTTP methods

  1. Create a RoutePolicy resource with your transformation rules. Make sure to create the RoutePolicy in the same namespace as the HTTPRoute resource. In the following example, you change the request path and HTTP method when a foo: bar header is present in the request.

    kubectl apply -f- <<EOF
apiVersion: gateway.kgateway.dev/v1alpha1
kind: RoutePolicy
metadata:
  name: transformation
  namespace: httpbin
spec:
  transformation:
    response:
      set:
      - name: ":path"
        value: '{% if request_header("foo") == "bar" %}/post{% else %}{{ request_header(":path") }}{% endif %}'
      - name: ":method"
        value: '{% if request_header("foo") == "bar" %}POST{% else %}{{ request_header(":method") }}{% endif %}'
EOF

  2. Update the HTTPRoute resource to apply the RoutePolicy to the httpbin route by using an extensionRef filter.

    kubectl apply -f- <<EOF
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: httpbin
  namespace: httpbin
  labels:
    example: httpbin-route
spec:
  parentRefs:
    - name: http
      namespace: kgateway-system
  hostnames:
    - "www.example.com"
  rules:
    - backendRefs:
        - name: httpbin
          port: 8000
      filters:
      - type: ExtensionRef
        extensionRef:
          group: gateway.kgateway.dev
          kind: RoutePolicy
          name: transformation
EOF

  3. Send a request to the /get endpoint of the httpbin app. Include the foo: bar request header to trigger the request transformation. Verify that you get back a 200 HTTP response code and that your request path is rewritten to the /post endpoint. The /post endpoint accepts requests only if the HTTP POST method is used. The 200 HTTP response code therefore also indicates that the HTTP method was successfully changed from GET to POST. 

    curl -vik http://$INGRESS_GW_ADDRESS:8080/get \
 -H "foo: bar" \
 -H "host: www.example.com:8080" 
    curl -vik localhost:8080/get \
-H "foo: bar" \
-H "host: www.example.com" \

    Example output:

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    < HTTP/1.1 200 OK
HTTP/1.1 200 OK
...  
{
  "args": {},
  "headers": {
     "Accept": [
       "*/*"
     ],
     "Content-Length": [
     "0"
     ],
     "Foo": [
     "bar"
     ],
     "Host": [
     "www.example.com:8080"
     ],
     "User-Agent": [
     "curl/7.77.0"
     ],
     "X-B3-Sampled": [
     "0"
     ],
     "X-B3-Spanid": [
     "5f36d131289dba78"
     ],
     "X-B3-Traceid": [
     "590047a63783206e5f36d131289dba78"
     ],
     "X-Forwarded-Proto": [
     "http"
     ],
     "X-Request-Id": [
     "6b7debde-6a8a-4d9e-90a4-33a9a35937d3"
     ]
 },
 "origin": "127.0.0.6:48539",
 "url": "http://www.example.com:8080/post",
 "data": "",
 "files": null,
 "form": null,
 "json": null
}

  4. Send another request to the /get endpoint of the httpbin app. This time, you omit the foo: bar header. Verify that you get back a 200 HTTP response code and that the request path is not rewritten to the /post endpoint. The /get endpoint accepts requests only if the HTTP GET method is used. A 200 HTTP response code therefore also verifies that the HTTP method was not changed. 

    curl -vik http://$INGRESS_GW_ADDRESS:8080/get \
 -H "host: www.example.com:8080" 
    curl -vik localhost:8080/get \
-H "host: www.example.com" \

    Example output:

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    < HTTP/1.1 200 OK
HTTP/1.1 200 OK
...

{
 "args": {},
 "headers": {
     "Accept": [
     "*/*"
     ],
     "Host": [
     "www.example.com:8080"
     ],
     "User-Agent": [
     "curl/7.77.0"
     ],
     "X-B3-Sampled": [
     "0"
     ],
     "X-B3-Spanid": [
     "a83c35458cc4a47b"
     ],
     "X-B3-Traceid": [
     "bf14b3d3098cd639a83c35458cc4a47b"
     ],
     "X-Forwarded-Proto": [
     "http"
     ],
     "X-Request-Id": [
     "b91ecfcf-4f79-4b65-9727-09aafcaeb40e"
     ]
 },
 "origin": "127.0.0.6:46209",
 "url": "http://www.example.com:8080/get"
}

Cleanup

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

  1. Delete the RoutePolicy resource.

    kubectl delete RoutePolicy transformation -n httpbin

  2. Remove the extensionRef filter from the HTTPRoute resource.

    kubectl apply -f- <<EOF
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: httpbin
  namespace: httpbin
  labels:
    example: httpbin-route
spec:
  parentRefs:
    - name: http
      namespace: kgateway-system
  hostnames:
    - "www.example.com"
  rules:
    - backendRefs:
        - name: httpbin
          port: 8000
EOF
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