Docker can't connect to redis from another service

Question

I can't figure out how to connect to my redis service from my app service. Using DDocker version 18.03.1-ce, build 9ee9f40ocker for Mac.

I've tried connecting the various ways I've found on similar questions:

const client = redis.createClient({ host: 'localhost', port: 6379});

const client = redis.createClient({ host: 'redis', port: 6379});

const client = redis.createClient('redis://redis:6379');

const client = redis.createClient('redis', 6379); // and reversed args

I always get some form of:

Error: Redis connection to localhost:6379 failed - connect ECONNREFUSED 127.0.0.1:6379

Error: Redis connection to redis:6379 failed - connect ECONNREFUSED 172.20.0.2:6379

Docker containers

$ docker ps
CONTAINER ID        IMAGE                COMMAND                  CREATED              STATUS              PORTS                    NAMES
0fd798d58561        app_app         "pm2-runtime start e…"   2 seconds ago        Up 7 seconds                                 app
65d148e498f7        app_redis       "docker-entrypoint.s…"   About a minute ago   Up 8 seconds        0.0.0.0:6379->6379/tcp   redis

Redis works:

$ docker exec -it redis /bin/bash
root@65d148e498f7:/data# redis-cli ping
PONG

Redis Dockerfile (pretty simple)

FROM redis:4.0.9
COPY redis.conf /usr/local/etc/redis/redis.conf
CMD ["redis-server", "/usr/local/etc/redis/redis.conf"]

app Dockerfile

FROM node:10.3.0-slim
RUN mkdir -p /app
COPY src/* /app/
CMD ["pm2-runtime", "start", "/app/ecosystem.config.js"]

docker-compose.yml

version: "3"
services:
  redis:
    build: ./redis/
    container_name: redis
    restart: unless-stopped
    ports:
      - "6379:6379"
    expose:
      - "6379"
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
    environment:
      - 'API_PORT=6379'
      - 'NODE_ENV=production'
  app:
    depends_on:
      - redis
    build: ./app/
    container_name: app
    restart: unless-stopped
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
      - /app/node_modules
    environment:
      - 'NODE_ENV=production'

Answer 1

Let me explain it in simple language. When you run docker-compose up it runs redis and app in separate containers. Now your app needs to connect/access the redis container (remember redis is not at your machines localhost, its inside a container and runs inside it at default port 6379). By default Docker will keep app container and redis container in same network and you can access a container by its service name (which in your case is redis and app) so in order to access redis from app container all you need is to use the default port 6379 and host will be the service name (in your case "redis").

For a node application running in a container get access to Redis (which was also running in a container) by

const redis = require("redis");
const client = redis.createClient(6379, "service-name-for-redis-container");