Criando um ambiente de desenvolvimento PHP com Docker Compose

docker-compose.yml

php:
  build: ./Dockerfile
  ports:
    - "81:81"
    - "443:443"
  volumes:
    - ./www:/var/www/html
  links: 
    - db  

db:
  image: mysql:5.7
  volumes:
   - /var/lib/mysql
  environment:
   - MYSQL_ROOT_PASSWORD=phprs
   - MYSQL_DATABASE=phprs    

Dockerfile

FROM php:5.6-apache

RUN docker-php-ext-install mysqli

index.php

<?php 
  echo "<pre><h2>Criando um ambiente de desenvolvimento PHP com Docker Compose.</h2></pre><br/>";
  mysqli_connect("db", "root", "phprs") or die(mysqli_error()); 
  echo "<pre><h3>Connected to MySQL<h3></pre><br/>";