docker compose file to build a redis cluster ?

docker-compose.yml

version: '2' 
services:
    db: 
        image: mysql
        ports:
            - "3306:3306"
        volumes:
            - ./mysql:/var/lib/mysql
        environment: # ???
            MYSQL_ROOT_PASSWORD: root
            MYSQL_ROOT_DATABASE: ""
            MYSQL_USER: root
            MYSQL_PASSWORD: root

    redis_master:
        image: redis:3.2-alpine
        volumes: 
            - ./redis_data:/data
    redis_slave:
        image: redis:3.2-alpine
        links:
            - "redis_master:master"
        command: redis-server --slaveof master 6379
    php:
        image: php 
        volumes: 
            - ./src:/var/www/html
        links:
            - redis_master
            - db
        ports:
            - "8080:80"
        command: php -S 0.0.0.0:80 -t /var/www/html/

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