What is wrong with this docker-compose?

Question

Docker

There is a docker-compose in which there are two services and a database that these two services should use (although this is not the top solution BUT ..) when I try to connect to this database, I constantly get errors .. If there are people who have solid experience with docker- oh, maybe they will immediately see where I'm wrong ...

version: "3.0"

networks:
  gitea:
    external: false

services:
  
  gitea:
    image: gitea/gitea:latest
    container_name: gitea
    restart: always
    environment:
      - USER_UID=1000
      - USER_GID=1000
      - DB_TYPE=mysql
      - DB_HOST=db:3306
      - DB_NAME=gitea
      - DB_USER=tester
      - DB_PASSWD=superpassword
    restart: always
    networks:
      - gitea
    volumes:
      - data_gitea:/data
      - timezone_gitea:/etc/timezone:ro
      - localtime_gitea:/etc/localtime:ro
    ports:
       - "3000:3000"
       - "222:22"
    depends_on:
      - db


  db:
    image: mysql:5.7
    container_name: gitea_mysql
    restart: always
    environment:
      - MYSQL_ROOT_PASSWORD=testertester78
      - MYSQL_USER=admin
      - MYSQL_PASSWORD=superpassword
      - MYSQL_DATABASE=nextcloud
    networks:
      - gitea
    volumes:
      - mysql_gitea:/var/lib/mysql
    ports:
      - "3306:3306"


  adminer:
    image: adminer:latest
    container_name: adminer
    restart: always
    ports:
      - "3128:8080"
    depends_on:
      - db


  nextcloud:
    image: nextcloud:latest
    container_name: nextcloud
    restart: always
    links:
      - db
    ports:
      - "80:80"
    volumes:
      - nextcloud:/var/www/html


volumes:
  data_gitea:
  timezone_gitea:
  localtime_gitea:
  mysql_gitea:
  nextcloud:

Answer 1

immediately that the
nextcloud container and the db container caught my eye are on different networks, more precisely, in the nextcloud container, you simply did not add the network. The links construct is obsolete, use shared networks, don't forget to describe them as described by volumes and everything will be fine