ws-example

README

ws-example

ws-example shows an simple example implementation of a Golang Websocket server. It is primarily an exploration of gorilla/websockets and nginx to proxy websocket connections.

Using nginx as a proxy, we can run multiple websocket servers and distribute connections among them.

See details below for running the application locally.

Running Locally

docker-compose

Simply running docker-compose up is enough to get the services up and functional. Connect a websocket client to http://localhost:8080/ws to interact with the websocket server.

An nginx service will start which proxies websocket connections to ws-backend-n. nginx is used to provide a single host to connect to (e.g. localhost:8080) but distribute requests across multiple backends.

The ws-backend-n services are a simple Golang application using gorilla/websocket that echoes back any message received but prepends the hostname to differentiate which backend host you are connected to.

Use websocat to connect as a client for demonstration purposes. It can be installed with Homebrew (brew install websocat).

For example:

$ websocat -E --ping-interval 5 --ping-timeout 10 ws://localhost:8080/ws

This gives an interactive shell to send and received messages to the backend. Type a message and press enter to see a response.

$ websocat -E --ping-interval 5 --ping-timeout 10 ws://localhost:8080/ws
[a9de44781391] hello :) type a message and press ENTER
hello
[a9de44781391] hello

Press CTRL+C to exit, with the -E this will close the connection immediately with the backend as well.

Docker Swarm

Docker Swarm can be used to emulate an environment that would be more similar to production. The docker-compose.swarm.yml can be used to deploy the service stack with one nginx service and, initially, one ws-backend service. From there, the ws-backend service can be scaled arbitrarily and nginx will automatically proxy requests to all backends.

Deploy websockets stack using docker-compose.swarm.yml

$ docker stack deploy --compose-file=docker-compose.swarm.yml websockets
Creating service websockets_nginx
Creating service websockets_ws-backend

View tasks in the websockets stack

$ docker stack ps websockets
ID                  NAME                      IMAGE                  NODE                DESIRED STATE       CURRENT STATE                ERROR                       PORTS
w992fkm1363w        websockets_nginx.1        nginx:1.19.2           carb                Running             Running about a minute ago                               
54ipaz8sal94        websockets_ws-backend.1   golang:1.15.2-buster   carb                Running             Running about a minute ago

Scale ws-backend service in stack

$ docker service scale websockets_ws-backend=2
websockets_ws-backend scaled to 2
overall progress: 2 out of 2 tasks 
1/2: running   [==================================================>] 
2/2: running   [==================================================>] 
verify: Service converged 

Use websocat to connect to the services

$ websocat -E --ping-interval 5 --ping-timeout 10 ws://localhost:8080/ws
[886396d2edcc] hello :) type a message and press ENTER
asdf
[886396d2edcc] asdf
...
$ websocat -E --ping-interval 5 --ping-timeout 10 ws://localhost:8080/ws
[1eba9cf95b52] hello :) type a message and press ENTER
adsf
[1eba9cf95b52] adsf

Note that we have connected to two different hosts 886396d2edcc and 1eba9cf95b52. This indicates that nginx is correctly proxying connections to an arbitrary number of backends and we are therefore naively load balancing the websocket connections.

View logs for ws-backend services

docker service logs -f websockets_ws-backend
websockets_ws-backend.2.plyyp6ztzydh@carb    | Got message: asdf
websockets_ws-backend.1.54ipaz8sal94@carb    | Got message: adsf