Wasm Extensions

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This task provides instructions for extending Envoy Gateway with WebAssembly (Wasm) extensions.

Wasm extensions allow you to extend the functionality of Envoy Gateway by running custom code against HTTP requests and responses, without modifying the Envoy Gateway binary. These extensions can be written in any language that compiles to Wasm, such as C++, Rust, AssemblyScript, or TinyGo.

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

Prerequisites

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

Expand for instructions

  1. Install the Gateway API CRDs and Envoy Gateway using Helm:

    helm install eg oci://docker.io/envoyproxy/gateway-helm --version v1.3.2 -n envoy-gateway-system --create-namespace

  2. Install the GatewayClass, Gateway, HTTPRoute and example app:

    kubectl apply -f https://github.com/envoyproxy/gateway/releases/download/v1.3.2/quickstart.yaml -n default

  3. Verify Connectivity:

    Get the External IP of the Gateway:

    export GATEWAY_HOST=$(kubectl get gateway/eg -o jsonpath='{.status.addresses[0].value}')

    Curl the example app through Envoy proxy:

    curl --verbose --header "Host: www.example.com" http://$GATEWAY_HOST/get

    The above command should succeed with status code 200.

    Get the name of the Envoy service created the by the example Gateway:

    export ENVOY_SERVICE=$(kubectl get svc -n envoy-gateway-system --selector=gateway.envoyproxy.io/owning-gateway-namespace=default,gateway.envoyproxy.io/owning-gateway-name=eg -o jsonpath='{.items[0].metadata.name}')

    Port forward to the Envoy service:

    kubectl -n envoy-gateway-system port-forward service/${ENVOY_SERVICE} 8888:80 &

    Curl the example app through Envoy proxy:

    curl --verbose --header "Host: www.example.com" http://localhost:8888/get

    The above command should succeed with status code 200.

Configuration

Envoy Gateway supports two types of Wasm extensions:

  • HTTP Wasm Extension: The Wasm extension is fetched from a remote URL.
  • Image Wasm Extension: The Wasm extension is packaged as an OCI image and fetched from an image registry.

The following example demonstrates how to configure an EnvoyExtensionPolicy to attach a Wasm extension to an EnvoyExtensionPolicy . This Wasm extension adds a custom header x-wasm-custom: FOO to the response.

HTTP Wasm Extension

This EnvoyExtensionPolicy configuration fetches the Wasm extension from an HTTP URL.

cat <<EOF | kubectl apply -f -
apiVersion: gateway.envoyproxy.io/v1alpha1
kind: EnvoyExtensionPolicy
metadata:
  name: wasm-test
spec:
  targetRefs:
  - group: gateway.networking.k8s.io
    kind: HTTPRoute
    name: backend
  wasm:
  - name: wasm-filter
    rootID: my_root_id
    code:
      type: HTTP
      http:
        url: https://raw.githubusercontent.com/envoyproxy/examples/main/wasm-cc/lib/envoy_filter_http_wasm_example.wasm
        sha256: 79c9f85128bb0177b6511afa85d587224efded376ac0ef76df56595f1e6315c0
EOF

Save and apply the following resource to your cluster:

---
apiVersion: gateway.envoyproxy.io/v1alpha1
kind: EnvoyExtensionPolicy
metadata:
  name: wasm-test
spec:
  targetRefs:
  - group: gateway.networking.k8s.io
    kind: HTTPRoute
    name: backend
  wasm:
  - name: wasm-filter
    rootID: my_root_id
    code:
      type: HTTP
      http:
        url: https://raw.githubusercontent.com/envoyproxy/examples/main/wasm-cc/lib/envoy_filter_http_wasm_example.wasm
        sha256: 79c9f85128bb0177b6511afa85d587224efded376ac0ef76df56595f1e6315c0

Verify the EnvoyExtensionPolicy status:

kubectl get envoyextensionpolicy/http-wasm-source-test -o yaml

Image Wasm Extension

This EnvoyExtensionPolicy configuration fetches the Wasm extension from an OCI image.

cat <<EOF | kubectl apply -f -
apiVersion: gateway.envoyproxy.io/v1alpha1
kind: EnvoyExtensionPolicy
metadata:
  name: wasm-test
spec:
  targetRefs:
  - group: gateway.networking.k8s.io
    kind: HTTPRoute
    name: backend
  wasm:
  - name: wasm-filter
    rootID: my_root_id
    code:
      type: Image
      image:
        url: zhaohuabing/testwasm:v0.0.1
EOF

Save and apply the following resource to your cluster:

---
apiVersion: gateway.envoyproxy.io/v1alpha1
kind: EnvoyExtensionPolicy
metadata:
  name: wasm-test
spec:
  targetRefs:
  - group: gateway.networking.k8s.io
    kind: HTTPRoute
    name: backend
  wasm:
  - name: wasm-filter
    rootID: my_root_id
    code:
      type: Image
      image:
        url: zhaohuabing/testwasm:v0.0.1

Verify the EnvoyExtensionPolicy status:

kubectl get envoyextensionpolicy/http-wasm-source-test -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:

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

You should see that the wasm extension has added this header to the response:

x-wasm-custom: FOO

Clean-Up

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

Delete the EnvoyExtensionPolicy:

kubectl delete envoyextensionpolicy/wasm-test

Next Steps

Checkout the Developer Guide to get involved in the project.