connect two docker containers with socket io - node.js

Question

I am currently working on dockerizing a tested socket.io app for a simple chat application, using socket.io, and mocha for testing. the server opens up a socket for listening on port 3000 and the test client uses the socket to emit messages or receive emissions.
I am using version 3 of docker compose files.
nodeserver dockerfile:
FROM node:10
WORKDIR /usr/src/appserver
COPY package*.json ./
COPY public public
COPY main.js main.js
RUN npm install
RUN npm install express
RUN npm install socket.io
CMD ["npm", "start"]
test dockerfile:
FROM nodeserver
COPY test test
RUN npm update && \
npm install -g mocha && \
npm install -g socket.io-client
CMD ["npm", "test"]
docker-compose:
version: "3"
services:
nodeserver:
build: .
expose:
- "3000"
image: ws
test:
depends_on:
- nodeserver
links:
- nodeserver
build: ./test
image: test_image
my node server is listening on port 3000, and on connection sends a hi message to all.
let express = require('express');
let app = express();
let http = require('http').createServer(app);
let io = require('socket.io')(http);
http.listen(3000, function ()
{
console.log('listening on *:3000');
});
io.on('connection', function(socket)
{
console.log('a user connected');
io.emit('hi', 'hi');
});
and my mocha test looks like this, which in essence attaches itself as a client and waits for the the hi message to come.
const url = 'ws://nodeserver:3000';
describe("Chat Server", function()
{
it("Should broadcast hi!", function(done)
{
let client1 = io.connect(url, options);
client1.on('connect', function()
{
client1.on('hi', function(msg)
{
msg.should.equal("hi");
client1.disconnect();
done();
});
});
});
}
running docker-compose, runs the nodeserver and the test client fails with timeout, which tells me the client cannot see the swarm network.
now running the dockers separately, that is exposing nodeservers to host and trying to connect to my localhost instead works perfectly and the test passes. This tells me that my socket and the way I communicate with nodeserver should be correct, which would basically mean that I should be having a problem with setting up my swarm's network. Can somebody tell me what I am doing wrong here?

Answer 1

I think your configuration looks good, it's a matter of readiness of your nodeserver. Even with depends_on, there is no guarantee that nodeserver is ready when test starts. (also links is useless and deprecated).
To verify my hypothesis, try the following sequence:
docker-compose up -d nodeserver
wait a few seconds
docker-compose up -d test