Cannot connect to MySQL db using docker container

Question

I wrote an application in Typescript which use Typeorm to interact with a MySQL database. When I run the app using npm run dev which is a package.json script, the connection is working fine with these credentials:

"type": "mysql",
"host": "127.0.0.1",
"port": 3306,
"username": "root",
"password": "root",
"database": "mydb",

but when I launch my Docker container I get:

> Error: connect ECONNREFUSED 127.0.0.1:3306
> errno: -111,
> code: 'ECONNREFUSED',
> syscall: 'connect',
> address: '127.0.0.1',
> port: 3306,
> fatal: true

I cannot figure out of this problem, I also tried to change 127.0.0.1 with localhost but same problem. That's weird 'cause I'm using Dbeaver to connect with my LAMP which is a Docker container container too and I can establish the connection.

Seems a problem related only with the containers connection, maybe the container of the app doesn't know the network 127.0.0.1?

This is my image file:

FROM node:stretch-slim

WORKDIR /myapp

COPY package.json ./
COPY ./dist ./dist

RUN npm install

EXPOSE 4000
ENV NODE_ENV development
ENV PORT 4000
ENV URL http://localhost:4000
ENV JWT_SECRET secret

CMD ["npm", "run", "start", "dev"]

and this is my docker-compose.yml:

version: '3'
services:
  app:
    container_name: myapp
    restart: always
    build: .
    ports:
      - '4000:4000'

for compile my containers I did: docker-compose up --build

What is wrong? As you can see from my lamp container each port is correctly exposed:

Answer 1

The problem here is that each container use their own network, even though I exposed the mysql container on port 3306 I cannot access to mysql from the myapp container, because myapp container use another network.

So executing the following command: docker network ls I was able to list all the networks available, and then I did:

docker network inspect bridge

which has returned the following gateway: 172.17.0.1

The solution would be to replace localhost with 172.17.0.1. But I don't like the following solution too much, so I rebuilded the myapp image adding previously network_mode inside the docker-compose.yml, so now I have:

version: '3'
services:
  app:
    container_name: myapp
    restart: always
    build: .
    ports:
      - '4000:4000'
    network_mode: 'host'

as documentation says:

If you use the host network mode for a container, that container’s network stack is not isolated from the Docker host (the container shares the host’s networking namespace), and the container does not get its own IP-address allocated. For instance, if you run a container which binds to port 80 and you use host networking, the container’s application is available on port 80 on the host’s IP address.

I don't know if there is a better solution out there, I'm a Docker noob so far, so maybe someone more expert on this could propose a better solution to share a container network such as mysql, and then access to that shared network from others containers.

Another solution would be "host": "host.docker.internal"