How to connect socket.io inside docker-compose between containers - docker

Question

I have one container that is serving http on port 4000.
it has socket server attached
docker-compose:
dashboard-server:
image: enginetonic:compose1.2
container_name: dashboard-server
command: node src/service/endpoint/dashboard/dashboard-server/dashboard-server.js
restart: on-failure
ports:
- 4000:4000
integration-test:
image: enginetonic:compose1.2
container_name: integration-test
testRegex "(/integration/.*|(\\.|/)(integration))\\.jsx?$$"
tty: true
server:
const http = require('http').createServer(handler)
const io = Io(http)
io.on('connection', socket => {
logger.debug('socket connected')
})
io.use((socket, next) => {
logger.debug('socket connection established.')
})
http.listen(4000, '127.0.0.1', () => {
console.log(
`Server running at http://127.0.0.1:4000/`
)
output in docker:
Server running at http://127.0.0.1:4000/
https is listening: true
Now, I am trying to connect to this server from another container like this:
file:
const url = `ws://dashboard-server:4000`
const ioc = IoC.connect(url)
ioc.on('error', error => {
console.log(error.message)
})
ioc.on('connect', res => {
console.log('connect')
})
ioc.on('connect_error', (error) => {
console.log(error.message)
})
output:
xhr poll error
When I run both locally in terminal, I get correct response
{"message":"socket connection established","level":"debug"}
Why isnt socket making connection inside container, but locally it is?
What am I doing wrong?
edit: only part of files are displayed for readability. socket connects normaly on local machine with with spawning both files in separate terminals

Answer 1

You need to link the docker containers and refer to them by name, not 127.0.0.1. https://docs.docker.com/compose/networking provides more doc. You'll also need to listen to '0.0.0.0' so that you accept connections across the docker network.
I only see one container in your compose file. If you're trying to connect to the docker containers from outside docker, you'll have to expose a port. The same reference shows you how.
http.listen(4000, '127.0.0.1', () => {
should become
http.listen(4000, '0.0.0.0', () => {
so that the server is listening on all addresses, including the address that docker is automatically allocating on a docker network.
Then the client has to refer to the server by the name given in docker compose, so
const url = `ws://127.0.0.1:4000`
becomes
const url = `ws://dashboard-server:4000`