issue redis and docker - docker

Question

I currently have a very strange error with docker more precisely with redis.
My backend runs with nodejs and typescript:
code
const redisPubSubOptions: any = {
host: process.env.REDIS_HOST || "127.0.0.1",
port: process.env.REDIS_PORT || 6379,
connectTimeout: 10000,
retryStrategy: (times: any) => Math.min(times * 50, 2000),
};
export const pubsub: RedisPubSub = new RedisPubSub({
publisher: new Redis(redisPubSubOptions),
subscriber: new Redis(redisPubSubOptions),
});
Dockerfile
FROM node:14-alpine as tsc-builder
WORKDIR /usr/src/app
COPY . .
RUN yarn install
EXPOSE 4000
CMD yarn run dev
docker-compose
version: "3.8"
services:
backend:
build: .
container_name: backend
ports:
- 4242:4242
depends_on:
- redis
env_file:
- ./docker/env/.env.dev
environment:
- ENVIRONMENT=development
- REDIS_PORT=6379
- REDIS_HOST=redis
redis:
image: redis:6.0.12-alpine
command: redis-server --maxclients 100000 --appendonly yes
hostname: redis
ports:
- "6379:6379"
restart: always
when I start my server the backend works and then the redis error comes after:
Error: connect ECONNREFUSED 127.0.0.1:6379

Answer 1

Both Redis and your backend run on different containers, so they have different IP addresses in the docker network. You are trying to connect to 127.0.0.1, which is the local address of the backend container.
Method 1:
Since you are using docker-compose (and of course it creates a network between services), you can use the service name instead of 127.0.0.1. For example:
const redisPubSubOptions: any = {
host: process.env.REDIS_HOST || "redis",
port: process.env.REDIS_PORT || 6379,
connectTimeout: 10000,
retryStrategy: (times: any) => Math.min(times * 50, 2000),
};
export const pubsub: RedisPubSub = new RedisPubSub({
publisher: new Redis(redisPubSubOptions),
subscriber: new Redis(redisPubSubOptions),
});
Method 2:
The other method is to expose the Redis port to the IP address of the Docker interface in the Host machine. Most of the time that is 172.17.0.1, but with ip -o a (If you are using Linux) you can see the Docker interface and its IP address.
so you need to do this for that:
redis:
image: redis:6.0.12-alpine
command: redis-server --maxclients 100000 --appendonly yes
hostname: redis
ports:
- "172.17.0.1:6379:6379"
restart: always
This address 172.17.0.1:6379 (Or any Docker interface IP address on the Host) should be exposed for Redis. Easily you can use this address in the application.
Note: You can handle these values using environment variable which is a better and more standard solution. You can take a look at this.