External Processing

This task provides instructions for configuring external processing.

External processing calls an external gRPC service to process HTTP requests and responses. The external processing service can inspect and mutate requests and responses.

Envoy Gateway introduces a new CRD called EnvoyExtensionPolicy that allows the user to configure external processing. This instantiated resource can be linked to a Gateway and HTTPRoute resource.

Prerequisites

Follow the steps from the Quickstart to install Envoy Gateway and the example manifest. Before proceeding, you should be able to query the example backend using HTTP.

Verify the Gateway status:

kubectl get gateway/eg -o yaml

GRPC External Processing Service

Installation

Install a demo GRPC service that will be used as the external processing service:

kubectl apply -f https://raw.githubusercontent.com/envoyproxy/gateway/latest/examples/kubernetes/ext-proc-grpc-service.yaml

Create a new HTTPRoute resource to route traffic on the path /myapp to the backend service.

cat <<EOF | kubectl apply -f -
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: myapp
spec:
  parentRefs:
  - name: eg
  hostnames:
  - "www.example.com"
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /myapp
    backendRefs:
    - name: backend
      port: 3000   
EOF

Save and apply the following resource to your cluster:

---
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: myapp
spec:
  parentRefs:
  - name: eg
  hostnames:
  - "www.example.com"
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /myapp
    backendRefs:
    - name: backend
      port: 3000   

Verify the HTTPRoute status:

kubectl get httproute/myapp -o yaml

Configuration

Create a new EnvoyExtensionPolicy resource to configure the external processing service. This EnvoyExtensionPolicy targets the HTTPRoute “myApp” created in the previous step. It calls the GRPC external processing service “grpc-ext-proc” on port 9002 for processing.

By default, requests and responses are not sent to the external processor. The processingMode struct is used to define what should be sent to the external processor. In this example, we configure the following processing modes:

  • The empty request field configures envoy to send request headers to the external processor.
  • The response field includes configuration for body processing. As a result, response headers are sent to the external processor. Additionally, the response body is streamed to the external processor.
cat <<EOF | kubectl apply -f -
apiVersion: gateway.envoyproxy.io/v1alpha1
kind: EnvoyExtensionPolicy
metadata:
  name: ext-proc-example
spec:
  targetRef:
    group: gateway.networking.k8s.io
    kind: HTTPRoute
    name: myapp
  extProc:
  - backendRefs:
    - name: grpc-ext-proc
      port: 9002
    processingMode:
      request: {}
      response: 
        body: Streamed 
EOF

Save and apply the following resource to your cluster:

---
apiVersion: gateway.envoyproxy.io/v1alpha1
kind: EnvoyExtensionPolicy
metadata:
  name: ext-proc-example
spec:
  targetRef:
    group: gateway.networking.k8s.io
    kind: HTTPRoute
    name: myapp
  extProc:
    - backendRefs:
        - name: grpc-ext-proc
          port: 9002
      processingMode:
        request: {}
        response: 
          body: Streamed

Verify the Envoy Extension Policy configuration:

kubectl get envoyextensionpolicy/ext-proc-example -o yaml

Because the gRPC external processing service is enabled with TLS, a BackendTLSPolicy needs to be created to configure the communication between the Envoy proxy and the gRPC auth service.

cat <<EOF | kubectl apply -f -
apiVersion: gateway.networking.k8s.io/v1alpha3
kind: BackendTLSPolicy
metadata:
  name: grpc-ext-proc-btls
spec:
  targetRefs:
  - group: ''
    kind: Service
    name: grpc-ext-proc
    sectionName: "9002"
  validation:
    caCertificateRefs:
    - name: grpc-ext-proc-ca
      group: ''
      kind: ConfigMap
    hostname: grpc-ext-proc.envoygateway
EOF

Save and apply the following resource to your cluster:

---
apiVersion: gateway.networking.k8s.io/v1alpha3
kind: BackendTLSPolicy
metadata:
  name: grpc-ext-proc-btls
spec:
  targetRefs:
    - group: ''
      kind: Service
      name: grpc-ext-proc
      sectionName: "9002"
  validation:
    caCertificateRefs:
      - name: grpc-ext-proc-ca
        group: ''
        kind: ConfigMap
    hostname: grpc-ext-proc.envoygateway

Verify the BackendTLSPolicy configuration:

kubectl get backendtlspolicy/grpc-ext-proc-btls -o yaml

Testing

Ensure the GATEWAY_HOST environment variable from the Quickstart is set. If not, follow the Quickstart instructions to set the variable.

echo $GATEWAY_HOST

Send a request to the backend service without Authentication header:

curl -v -H "Host: www.example.com" "http://${GATEWAY_HOST}/myapp"

You should see that the external processor added headers:

  • x-request-ext-processed - this header was added before the request was forwarded to the backend
  • x-response-ext-processed- this header was added before the response was returned to the client
curl -v -H "Host: www.example.com"  http://localhost:10080/myapp
[...]
< HTTP/1.1 200 OK
< content-type: application/json
< x-content-type-options: nosniff
< date: Fri, 14 Jun 2024 19:30:40 GMT
< content-length: 502
< x-response-ext-processed: true
<
{
 "path": "/myapp",
 "host": "www.example.com",
 "method": "GET",
 "proto": "HTTP/1.1",
 "headers": {
[...] 
  "X-Request-Ext-Processed": [
   "true"
  ],
[...]
 }

Clean-Up

Follow the steps from the Quickstart to uninstall Envoy Gateway and the example manifest.

Delete the demo auth services, HTTPRoute, EnvoyExtensionPolicy and BackendTLSPolicy:

kubectl delete -f https://raw.githubusercontent.com/envoyproxy/gateway/latest/examples/kubernetes/ext-proc-grpc-service.yaml
kubectl delete httproute/myapp
kubectl delete envoyextensionpolicy/ext-proc-example
kubectl delete backendtlspolicy/grpc-ext-proc-btls

Next Steps

Checkout the Developer Guide to get involved in the project.