Rewrite dynamic path segments

Use the with() and regexReplace() CEL functions together with request.path to rewrite dynamic path segments before forwarding the request to the upstream.

with() binds a complex expression to a temporary variable to avoid evaluating it multiple times. regexReplace() replaces text matching a regular expression with a replacement string. Together, they are useful for sanitizing dynamic values such as replacing numeric IDs in a path with a placeholder before the request reaches the upstream service.

Before you begin

1. Set up an agentgateway proxy.
2. Install the httpbin sample app.

Rewrite dynamic path segments

In this example, you bind request.path to a temporary variable using with(), then use regexReplace() to replace any numeric path segments with id. Setting the result on the :path pseudo header rewrites the actual request that is path forwarded to the upstream service.

For example, a request to /users/12345 is forwarded upstream as /users/id.

1. Create an AgentgatewayPolicy resource with your transformation rules.

   kubectl apply -f- <<EOF
   apiVersion: agentgateway.dev/v1alpha1
   kind: AgentgatewayPolicy
   metadata:
     name: transformation
     namespace: httpbin
   spec:
     targetRefs:
     - group: gateway.networking.k8s.io
       kind: HTTPRoute
       name: httpbin
     traffic:
       transformation:
         request:
           set:
           - name: :path
             value: 'request.path.with(p, p.regexReplace("/[0-9]+", "/id"))'
   EOF

2. Send a request to the httpbin app using a path with a numeric ID. Verify that you get back a 200 HTTP response code and that the url field in the response body shows the normalized path forwarded to the upstream.

   Cloud Provider LoadBalancerPort-forward for local testing

   curl -vi http://$INGRESS_GW_ADDRESS:80/anything/users/12345 \
    -H "host: www.example.com:80"

   curl -vi localhost:8080/anything/users/12345 \
   -H "host: www.example.com"

   Example output:

   < HTTP/1.1 200 OK
   HTTP/1.1 200 OK
   ...
   
   {
     "args": {},
     "headers": {
       "Accept": [
         "*/*"
       ],
       "Host": [
         "www.example.com"
       ],
       "User-Agent": [
         "curl/8.7.1"
       ]
     },
     "origin": "10.244.0.6:12345",
     "url": "http://www.example.com/anything/users/id"
   }
   

Cleanup

kubectl delete AgentgatewayPolicy transformation -n httpbin