econnrefused rabbitMQ between docker containers

Question

I am trying to set up a simple docker-compose file which includes a rabbitmq container and a simple express server which connects to rabbitmq. I'm getting the following error when trying to connect to rabbitmq from my express application:

Error: connect ECONNREFUSED 172.19.0.2:5672
    at TCPConnectWrap.afterConnect [as oncomplete] (node:net:1247:16) {
  errno: -111,
  code: 'ECONNREFUSED',
  syscall: 'connect',
  address: '172.19.0.2',
  port: 5672
}

I checked the IP-adress of the docker network manually to verify that 172.19.0.2 is indeed the rabbitmq process, which it is.

Here is my docker-compose:

version: '3'
services:
  rabbitmq:
    image: rabbitmq:3-management-alpine
    container_name: 'rabbitmq'
    environment:
      - RABBITMQ_DEFAULT_USER=admin
      - RABBITMQ_DEFAULT_PASS=pass
    ports:
      - 5672:5672
      - 15672:15672
  producerexpress:
    build: ./service1
    container_name: producerexpress
    ports:
      - 3000:3000
    environment:
      - PORT=3000
    depends_on:
      - rabbitmq

and the express app and its docker file:

const express = require('express');
const app = express();
const port = process.env.PORT || 3000;
const amqp = require('amqplib');

const amqpUrl = process.env.AMQP_URL || 'amqp://admin:pass@172.19.0.2:5672';

let channel;
let connection;

connect();

async function connect(){
  try{
    connection = await amqp.connect(amqpUrl);
    channel = await connection.createChannel();

    await channel.assertQueue('chatExchange', {durable: false});
  } catch (err) {
    console.log(err);
  }
}

function sendRabbitMessage(msg) {
  channel.sendToQueue('chatExchange', Buffer.from(msg));
}


app.get('/', (req, res) => {
  let msg = 'Triggered by get request';
  sendRabbitMessage(msg);
  res.send('Sent rabbitmq message!');
});


app.listen(port, () => {
    console.log(`Server started on port ${port}`);
} );

FROM node:16

WORKDIR /app

COPY package*.json ./

RUN npm install

COPY . .

ENV PORT=3000

ENV AMQP_URL=amqp://admin:pass@172.19.0.2:5672

EXPOSE 3000

CMD ["npm", "start"]

This is my first time using docker compose and all the fixes I found on here seem to suggest I did everything correctly. What am I missing?

Answer 1

TL;DR
The depends_on guarantes the order in which the services will start up, but that doesn't guarante anything for the processes they inititate.

In these cases, you should expand the depends_on statement in order to take into account the health status of the process of interest

---

Firstly, you should avoid making the communication of cointainers depend on their IP address but instead rely on their service names, since you are using docker compose.

Meaning, instead of amqp://admin:pass@172.19.0.2:5672

You should use amqp://admin:pass@rabbitmq:5672

---

Moving on to the core issue, your producerexpress relies on to rabbitmq in order to function.

As a result, you added the depends_on statement to producerexpress to resolve this. But this is not enough, quotting from https://docs.docker.com/compose/startup-order/

You can control the order of service startup and shutdown with the depends_on option. Compose always starts and stops containers in dependency order, .... However, for startup Compose does not wait until a container is “ready” (whatever that means for your particular application) - only until it's running .

As a result, you need to add a health check in order to guarantee that the rabbitmq process has started successfully, not just the container .

In order to achieve that you should alter your compose file

version: '3'
services:
  rabbitmq:
    build: ./rabbitmq
    container_name: 'rabbitmq'
    environment:
      - RABBITMQ_DEFAULT_USER=admin
      - RABBITMQ_DEFAULT_PASS=pass
    ports:
      - 5672:5672
      - 15672:15672
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost:15672"]
      interval: 30s
      timeout: 10s
      retries: 5

  producerexpress:
    build: ./service1
    restart: on-failure
    container_name: producerexpress
    ports:
      - 3000:3000
    environment:
      - PORT=3000
    depends_on:
      rabbitmq:
        condition: service_healthy

In order to make the healthcheck, we need the curl package in the rabbitmq image, so add the following Dockerfile

FROM rabbitmq:3-management-alpine
RUN apk update
RUN apk add curl
EXPOSE 5672 15672

Finally, to make this change compatible create the following directory structure

./docker-compose.yml
./rabbitmq/
 --- Dockerfile
./service1/
 --- Dockerfile