alpine-nginx-php | Nginx running in Alpine with PHP | Continuous Deployment library

Using the following dockerfile, I'm trying to create a folder which is writable for PHP.

I have a Dockerfile for my Symfony application but the container doesn't have write permissions into the cache and logs directories.

I tried with the Symfony docs for permissions, but it is not working. I already set the container user to root, but the problem is the same.

Here is my Dockerfile:

How can I run a Docker image with NGINX, phpBB (and all required stuff like php installed) with persistence (Changes on the board shouldn't be lost) and with the database on another host (which already exists). So, let's assume I have the following: MySQL on 192.168.2.233 (local address) on port 3307 running. Now I want to create a Docker image with Alpine Linux (The smallest propably), NGINX and phpBB where the board runs on the NGINX webserver and connects to the database. Changes on the board (E.g. changing the webserver settings or so) should be persisted within the container. How can I do that?

EDIT:

The database on server 192.168.2.233 is already existing! So no, I don't need two or more Docker containers. I need one Docker container with phpBB running on the NGINX webserver and connecting to the database on another host in the same network. The container should use persistence (volumes) to save the settings made in phpBB.

I tried to use the following Dockerfile and modified it: https://gitlab.com/boxedcode/alpine-nginx-php-fpm/blob/master/Dockerfile --> https://drive.google.com/open?id=1CW68OFCJE9RjIe8_RBC8q5Fa6juRtxmR