My docker-compose.yml looks like this:

version: '3'

services:
  api:
    build:
      context: .
      dockerfile: Dockerfile
    image: api
    container_name: app-api
    restart: unless-stopped
    env_file: ./.env
    ports:
      - '8080:8080'
    volumes:
      - ./src
      - ./node_modules
    command: yarn start
    depends_on:
      - mysql
  mysql:
    container_name: app-mysql
    restart: always
    image: mysql:8.0.21
    environment:
      MYSQL_ROOT_PASSWORD: 'root'
      MYSQL_USER: 'app'
      MYSQL_PASS: 'password'
      MYSQL_DATABASE: 'appdb'
    volumes:
      - ./data:/var/lib/mysql
    ports:
      - '3307:3306'

My .env looks like this:

DB_HOST="mysql" // Tried 127.0.0.1, 0.0.0.0
DB_PORT="3306"
DB_USER="app"
DB_PASSWORD="password"
DB_NAME="appdb"
NODE_ENV="DEV"

Error I'm getting from the service: {"message":"Database connection failed with error Error: getaddrinfo ENOTFOUND \"mysql\"","level":"info","timestamp":"2020-07-27T03:57:55.524Z"}

I can connect with root from MySQL Workbench, I can't connect with user app. If the api is started without being in a docker container, it can connect to local db.

Seems like it just can't resolve the host at all, is this a DNS issue? I can't remember if I had the same issue when mysql wasn't dockerized, but it couldn't connect to a db that is outside a container. What am I doing wrong.

Edit: commenting out the whole mysql service has no impact at all, error message is same.