Generate request tracing headers

Use the uuid() and random() CEL functions to inject dynamically generated values into request headers. uuid() generates a unique UUIDv4 string on each request, useful for correlation IDs in distributed tracing. random() returns a float between 0.0 and 1.0, useful for probabilistic sampling decisions.

Before you begin

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

Generate request tracing headers

Tracing every request can be expensive at high traffic volumes. A common pattern is to inject a unique ID for correlation and a random value that a downstream tracing backend uses to decide whether to record a full trace, keeping only a percentage of all requests.

In this example, two headers are injected on every incoming request before it is forwarded upstream:

• x-request-id: A unique UUIDv4 generated by uuid(), used to correlate the request across services.
• x-sampling-decision: A random float from the random() function. For example, you might have a tracing backend that is configured to sample requests only if the x-sampling-decision header is set to 0.1 or less.

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: x-request-id
             value: 'uuid()'
           - name: x-sampling-decision
             value: 'string(random())'
   EOF

   The expression breaks down as follows:

   • uuid(): Generates a new UUIDv4 string for each request, such as f47ac10b-58cc-4372-a567-0e02b2c3d479.
   • random(): Generates a random float between 0.0 and 1.0, such as 0.4731. Wrap the transformation in string() so the value can be set as a header string.

2. Send a request and verify that both headers are present in the forwarded request.

   Cloud Provider LoadBalancerPort-forward for local testing

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

   curl -vi localhost:8080/get \
   -H "host: www.example.com"

   Example output:

   < HTTP/1.1 200 OK
   HTTP/1.1 200 OK
   ...
   {
     "headers": {
       "X-Request-Id": [
          "81895ac3-0b2b-45cb-901d-068b517c7262"
       ],
       "X-Sampling-Decision": [
          "0.32929987260956217"
       ]
       ...
     },
     ...
   }
   

   Each request produces a different X-Request-Id value. The X-Sampling-Decision value varies between 0.0 and 1.0 on each request.

Cleanup

kubectl delete AgentgatewayPolicy transformation -n httpbin