Golang filter

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

The example demonstrates a Go plugin that can respond directly to requests and also update responses provided by an upstream server.

It also shows how Go plugins can be independently configured at runtime.

Step 1: Compile the go plugin library

Change to the examples/golang directory and build the go plugin library.

$ pwd
envoy/examples/golang
$ docker compose -f docker-compose-go.yaml run --rm go_plugin_compile

The compiled library should now be in the lib folder.

$ ls lib
simple.so

Step 2: Start all of our containers

Start all the containers.

$ docker compose pull
$ docker compose up --build -d
$ docker compose ps

      Name                      Command               State                          Ports
-----------------------------------------------------------------------------------------------------------------------
golang_proxy_1         /docker-entrypoint.sh /usr ...   Up      10000/tcp, 0.0.0.0:10000->10000/tcp,:::10000->10000/tcp
golang_web_service_1   /bin/echo-server                 Up      8080/tcp

Step 3: Make a request handled by the Go plugin

The output from the curl command below should include the header added by the simple Go plugin.

$ curl -v localhost:10000 2>&1 | grep rsp-header-from-go
< rsp-header-from-go: bar-test

Step 4: Make a request handled upstream and updated by the Go plugin

The output from the curl command below should include the body that has been updated by the simple Go plugin.

$ curl localhost:10000/update_upstream_response 2>&1 | grep "updated"
upstream response body updated by the simple plugin

Step 5: Make a request handled by the Go plugin using custom configuration

The output from the curl command below should include the body that contains value of prefix_localreply_body by the simple Go plugin.

$ curl localhost:10000/localreply_by_config  2>&1 | grep "localreply"
Configured local reply from go, path: /localreply_by_config