使用docker的多个nginx / php应用程序的体系结构

I've been running most of my apps on single nginx/php-fpm installation directly on vps. I've decided to try out docker, and have been playing with it for a week now. I've read everything possible and believe I understand its concepts.

But I cannot wrap my head around having so many instances of nginx, php and db.

One thing I settled with is that I want to have 1 db, so that's easy:

mariadb:
  image: mariadb:latest
  container_name: mariadb
  ports:
    - "127.0.0.1:3306:3306"
  restart: always
  environment:
    MYSQL_ROOT_PASSWORD: xxxxx
  volumes:
    - /srv/mysql:/var/lib/mysql

I also found nginx-proxy together with nginx-certs work like charm:

nginx-proxy:
  image: jwilder/nginx-proxy
  container_name: nginx-proxy
  ports:
    - "80:80"
    - "443:443"
  restart: always
  volumes:
    - /srv/certs:/etc/nginx/certs:ro
    - /var/run/docker.sock:/tmp/docker.sock:ro
    - ./vhost.d:/etc/nginx/vhost.d
    - /usr/share/nginx/html


nginx-certs:
  image: jrcs/letsencrypt-nginx-proxy-companion
  container_name: nginx-certs
  volumes:
    - /srv/certs:/etc/nginx/certs:rw
    - /var/run/docker.sock:/var/run/docker.sock:ro
  volumes_from:
    - nginx-proxy

This is all dandy. But how do I handle actual app containers?

I want to keep ram usage to minimum, so what is recommended:

1. 1 php-fpm container with multiple volumes inside and multiple nginx servers
2. 1 nginx server and multiple php-fpm containers?
3. have 1 container per project and keep nginx/php-fpm inside that container
4. X nginx containers + X php-fpm containers. X amount of apps.

Any ideas?