使用Docker运行Laravel artisan命令时连接被拒绝

I'm running Laravel 5.4 in Docker. This is my docker-compose.yml file:

version: '2'

services:
  app:
    container_name: laravel_app
    image: webdevops/php-apache-dev:ubuntu-16.04
    links:
      - mysql
    depends_on:
      - mysql
    ports:
      - 8888:80
    volumes:
      - .:/app
    environment:
      docker: 'true'
      WEB_DOCUMENT_ROOT: '/app/public'
      WEB_NO_CACHE_PATTERN: '\.(.*)$$'
      working_dir: '/app'
  mysql:
    image: mariadb:latest
    ports:
      - 8889:80
    environment:
      MYSQL_ROOT_PASSWORD: 'dev'
      MYSQL_DATABASE: 'dev'
      MYSQL_USER: 'dev'
      MYSQL_PASSWORD: 'dev'

This is the relevant part of my .env file:

DB_CONNECTION=mysql
DB_HOST=mysql
DB_PORT=8889
DB_DATABASE=dev
DB_USERNAME=dev
DB_PASSWORD=dev

I am able to see the Laravel welcome page - that side of things works. But when I run php artisan migrate I get this error:

SQLSTATE[HY000] [2002] Connection refused (SQL: select * from information_schema.tables where table_schema = dev and table_name = migrations)

I have tried fiddling with the host and port parameters in the .env file.