In this guide, you use an Inja function to extract an environment variable value from the gateway proxy pod and add this value to the dynamic metadata filter in Envoy. Then, you inject the value that you stored in the dynamic metadata filter when writing access logs.

Before you begin

  1. Follow the Get started guide to install Gloo Gateway.

  2. Follow the Sample app guide to create a 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 gloo-system gloo-proxy-http -o jsonpath="{.status.loadBalancer.ingress[0]['hostname','ip']}")
echo $INGRESS_GW_ADDRESS  
  
      kubectl port-forward deployment/gloo-proxy-http -n gloo-system 8080:8080

Enrich access logs

  1. Follow the steps to enable access logs on your gateway proxy.

  2. Create a GlooTrafficPolicy with the following transformation rules:

    • The env Inja function is used to extract the POD_NAME environment variable from the gateway proxy pod.
    • The value of the environment variable is added to the pod_name key in the dynamic metadata values.
      kubectl apply -f- <<EOF
apiVersion: gloo.solo.io/v1alpha1
kind: GlooTrafficPolicy
metadata:
  name: transformation
  namespace: httpbin
spec:
  targetRefs:
  - group: gateway.networking.k8s.io
    kind: HTTPRoute
    name: httpbin
  glooTransformation:
    stages:
      early:
        requests:
        - transformation:
            template:
              dynamicMetadataValues:
                - key: 'pod_name'
                  value: '{{ env("POD_NAME") }}'
EOF

  3. Update the HTTPListenerPolicy resource to include the pod_name from the dynamic metadata values.

      kubectl apply -f- <<EOF
apiVersion: gateway.kgateway.dev/v1alpha1
kind: HTTPListenerPolicy
metadata:
  name: access-logs
  namespace: gloo-system
spec:
  targetRefs:
  - group: gateway.networking.k8s.io
    kind: Gateway
    name: http
  accessLog:
  - fileSink:
      path: /dev/stdout
      jsonFormat:
          start_time: "%START_TIME%"
          method: "%REQ(X-ENVOY-ORIGINAL-METHOD?:METHOD)%"
          path: "%REQ(X-ENVOY-ORIGINAL-PATH?:PATH)%"
          protocol: "%PROTOCOL%"
          response_code: "%RESPONSE_CODE%"
          response_flags: "%RESPONSE_FLAGS%"
          bytes_received: "%BYTES_RECEIVED%"
          bytes_sent: "%BYTES_SENT%"
          total_duration: "%DURATION%"
          resp_backend_service_time: "%RESP(X-ENVOY-UPSTREAM-SERVICE-TIME)%"
          req_x_forwarded_for: "%REQ(X-FORWARDED-FOR)%"
          user_agent: "%REQ(USER-AGENT)%"
          request_id: "%REQ(X-REQUEST-ID)%"
          authority: "%REQ(:AUTHORITY)%"
          backendHost: "%UPSTREAM_HOST%"
          backendCluster: "%UPSTREAM_CLUSTER%"
          pod_name: '%DYNAMIC_METADATA(io.solo.transformation:pod_name)%'
EOF

  4. Send another request to the httpbin app.

      curl -i http://$INGRESS_GW_ADDRESS:8080/status/200 -H "host: www.example.com:8080"
  
      curl -i localhost:8080/status/200 -H "host: www.example.com:8080"

  5. Review the access logs and verify that the pod_name is now injected into your access logs.

      kubectl -n gloo-system logs deployments/http | tail -1 | jq --sort-keys

    Example output:

      {
  "authority": "www.example.com:8080",
  "bytes_received": 0,
  "bytes_sent": 0,
  "method": "GET",
  "path": "/status/200",
  "pod_name": "http-844ff8bc4d-dh4pn",
  "protocol": "HTTP/1.1",
  "req_x_forwarded_for": null,
  "request_id": "132892e6-085e-400f-98da-c055ca04b714",
  "resp_upstream_service_time": "2",
  "response_code": 200,
  "response_flags": "-",
  "start_time": "2025-05-14T16:43:07.506Z",
  "total_duration": 2,
  "upstreamCluster": "kube-svc_httpbin-httpbin-8000_httpbin_httpbin_httpbin_8000",
  "upstreamHost": "10.0.12.250:8080",
  "user_agent": "curl/8.7.1"
}

Cleanup

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

  kubectl delete glootrafficpolicy transformation -n httpbin
kubectl delete httplistenerpolicy access-logs -n gloo-system