Why docker-compose do not use port binding as expected? - docker

Question

I'm using this docker-compose config for running a classic nodejs app + mysql + redis:
version: '3'
services:
app:
container_name: app
restart: always
build:
context: ./app/
depends_on:
- db
- redis
- elasticsearch
links:
- db
- redis
- elasticsearch
ports:
- "127.0.0.1:${APP_PORT}:${APP_PORT}"
environment:
- "PORT=${APP_PORT}"
- "MYSQL_PORT=${MYSQL_PORT}"
- "REDIS_PORT=${REDIS_PORT}"
redis:
container_name: redis
image: "redis:3-alpine"
restart: always
ports:
- "127.0.0.1:${REDIS_PORT}:6379"
db:
container_name: db
image: mariadb:10.0.30
restart: always
volumes:
- "${MYSQL_DATA_LOCATION}/data:/var/lib/mysql:delegated"
- "${MYSQL_DATA_LOCATION}/my.cnf:/etc/mysql/my.cnf:ro"
ports:
- "127.0.0.1:${MYSQL_PORT}:3306"
environment:
- "MYSQL_ROOT_PASSWORD=${MYSQL_ROOT_PASSWORD}"
- "MYSQL_USER=${MYSQL_USER}"
- "MYSQL_PASSWORD=${MYSQL_PASSWORD}"
- "MYSQL_DATABASE=${MYSQL_DATABASE}"
I'm also using a .env file containing the following values:
APP_PORT=5000
MYSQL_PORT=3306
REDIS_PORT=6379
And I start the application with
docker-compose up -d
Everything runs fine this way. I can change the mysql port without error, but if I change the redis port to something else than the original port, I have the following error in the app, when I use this config:
redis.createClient({host: 'redis', port: process.env.REDIS_PORT });
I get the following message:
Error: Redis connection to redis:5555 failed - connect ECONNREFUSED 172.18.0.3:5555
Whereas the connection between the db and the app works correctly :s
In docker ps I can see that the machine started with the expected config:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
9c594c6d98b8 nginx:mainline-alpine "nginx -g 'daemon of…" 33 seconds ago Up 39 seconds 0.0.0.0:2000->80/tcp webproxy
62d1f917d7ff app "npm run docker-debug" 36 seconds ago Up 42 seconds 127.0.0.1:5000->5000/tcp, 127.0.0.1:9222->9222/tcp app
7c982d543a7d mariadb:10.0.30 "docker-entrypoint.s…" 39 seconds ago Up 45 seconds 127.0.0.1:4000->3306/tcp db
9dd13967b37d redis:3 "docker-entrypoint.s…" 39 seconds ago Up 44 seconds 127.0.0.1:5555->6379/tcp redis
I can see here that the db is mapped from 4000 to 3306, which works, but the redis mapping from 5555 to 6379 is ignored. And if I manually change the port in the app connection to port 6379, it does work...
Is there something missing in my configuration ?

Answer 1

the redis is running inside the container on port 6379 period (if you dont change the port in its config). On your host you map port 5555 to redis container 6379. All services in docker-compose are visible to each other and you dont even need to EXPOSE those ports to host. In your app settings if you access the redis by redis://redis:6379 will work or with the exposed port redis://HOST_IP:5555 will work too