Lua filter

In this example, we show how the Lua filter can be used with the Envoy proxy.

The example Envoy proxy configuration includes two Lua filters that contain two different functions:

envoy_on_request(request_handle)
envoy_on_response(response_handle)

See here for an overview of Envoy’s Lua filter and documentation regarding these functions.

Step 1: Build the sandbox

Change to the examples/lua directory.

$ pwd
envoy/examples/lua
$ docker compose pull
$ docker compose up --build -d
$ docker compose ps

    Name                     Command               State             Ports
--------------------------------------------------------------------------------------------
lua_proxy_1         /docker-entrypoint.sh /bin ... Up      10000/tcp, 0.0.0.0:8000->8000/tcp
lua_web_service_1   node ./index.js                Up      0.0.0.0:8080->80/tcp

Step 2: Send a request to the service

The output from the curl command below should include the header added by the Lua filter.

Terminal 1

$ curl -v localhost:8000 2>&1 | grep Foo
Foo: bar                              <-- This is added by the common Lua filter. --<

Step 3: Using multiple Lua filters at the same time

Two Lua filters are configured in the example Envoy proxy configuration. But the second one can only work at a specific route.

The output from the curl command below should include the headers that added by multiple Lua filters.

Terminal 1

curl -v localhost:8000/multiple/lua/scripts 2>&1 | grep header_key_1
< header_key_1: header_value_1        <-- This is added by the second route-specific Lua filter. --<