How to connect a Node.js TCP-client in container A to a TCP-server in container B with Docker Compose? - node.js

Question

I am trying to connect a TCP-client in container A to a TCP-server in container B. Running docker-compose up results in a ECONNREFUSED error on the client side. 为什么呢？
The TCP-client looks like this:
var net = require('net');
var client = new net.Socket();
client.connect(1337, function() {
console.log('Connected');
client.write('Hello, server! Love, Client.');
});
client.on('data', function(data) {
console.log('Received: ' + data);
// client.destroy(); // kill client after server's response
});
client.on('close', function() {
console.log('Connection closed');
});
The TCP-client Dockerfile looks like this:
FROM node:latest
RUN mkdir /app
WORKDIR /app
ADD . /app
ADD package.json /app
RUN npm install
EXPOSE 1337
ENV PATH /app/node_modules/.bin:$PATH
CMD npm start
The TCP-server looks like this:
var net = require('net');
var server = net.createServer(function(socket) {
socket.write('Echo server\r\n');
socket.pipe(socket);
});
server.listen(1337);
The TCP-server Dockerfile looks like this:
FROM node:latest
RUN mkdir /app
WORKDIR /app
ADD . /app
ADD package.json /app
RUN npm install
EXPOSE 1337
ENV PATH /app/node_modules/.bin:$PATH
CMD npm start
The docker-compose.yml looks like this:
version: "3"
services:
tcpclient:
build: ./tcpclient
ports:
- "8000:8000"
depends_on:
- tcpserver
tcpserver:
build: ./tcpserver
ports:
- "8001:1337"
The connection error looks like this:
tcpclient_1 | > http-service#1.0.0 start /app
tcpclient_1 | > node tcpclient.js
tcpclient_1 |
tcpclient_1 | events.js:137
tcpclient_1 | throw er; // Unhandled 'error' event
tcpclient_1 | ^
tcpclient_1 |
tcpclient_1 | Error: connect ECONNREFUSED 127.0.0.1:1337
tcpclient_1 | at Object._errnoException (util.js:1003:13)
tcpclient_1 | at _exceptionWithHostPort (util.js:1024:20)
tcpclient_1 | at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1194:14)
tcpclient_1 | npm ERR! code ELIFECYCLE
Help would be greatly appreciated

Answer 1

Multiple problems here.
I'm not sure localhost from a container will be in the same interface than your host. Moreover, the port bound is 8001. But, I would recomand another approach:
Using link you can reference other containers hosts with their name.
I would try to:
1) Add in tcpclient container definition:
links:
- tcpserver
2) Keep 1337:1337 in tcp server (why is client exposing a TCP port btw ?)
3) use client.connect(1337, 'tcpserver', function(...){...}