kolaente/database-backup

version: '2'
services:
  backup:
    image: kolaente/database-backup
    restart: unless-stopped
    environment:
      CRON_TIME: 0 */12 * * *
      DB_BACKUP_MAX: '5'
    volumes:
      - ./config:/config
      - /srv/backups:/backups
      - /etc/localtime:/etc/localtime:ro
    networks:
      - default
      - backup

networks:
  backup:
    external: true

Place backup_hosts.json in config dir. Add db containers to backup network.