LAMP-Stack with Docker：如何修改httpd.conf以访问PHP-FPM？

Question

I have some trouble to get access from my apache container to Php-fpm. My docker-compose file is ready and works fine. But I don't know how to modify the httpd.conf in order to establish communication between both containers (Apache and Php-fpm). I have looked for some useful tutorials on the internet, but everyone uses Nginx instead of Apache2. There is also a preconfigured Docker image consisting of a Apache webserver and Php-fpm on Docker Hub, but I prefer two seperated images, because of replaceability.

Here is my docker-compose file:

version: "3.5"

services:
  webserver:
    build: apache/
    ports:
           - "8080:80"
           - "443:443"
    volumes: 
             - ~/Docker-Images/example/apache/html:/usr/local/apache2/htdocs
    links: 
           - php-fpm

  php-fpm:
    build: php-fpm/
    ports:
           - "9000:9000"
    links: 
           - database


  database:
    build: mysql/
    ports: 
           - "3306:3306"
    volumes:
             - ~/Docker-Images/example/mysql/init-scripts:/init-scripts


volumes:
  webserver:
  database:

If you need my httpd.conf, let me know! I haven't added it, because it is a very long file with only default values.