docker-compose and persistent storage problem

Question

I'm new with docker and docker-compose, and I have issue with persistent storage. I have three folders that I need to keep files outside of docker. I don't know what I'm doing wrong.

docker-compose.yaml

version: '3.3'

services:
    webserver:
        build:
              context: ./
              dockerfile: webserver.DockerFile
        ports:
            - 80:80
            - 443:443
        volumes:
            - html:/var/www/html
            - platforms:/var/www/platforms
            - sites-available:/etc/apache2/sites-available
    mysql-server:
        image: mysql:8.0.20
        restart: always
        environment:
              MYSQL_ROOT_PASSWORD: somepassword555

    phpmyadmin:
        image: phpmyadmin/phpmyadmin:5.0.1
        restart: always
        environment:
                PMA_HOST: mysql-server
                PMA_USER: root
                PMA_PASSWORD: somepassword555
        ports:
                - "8080:80"

When I run build on this, I get empty folders in webserver. Folders on host are not empty.

EDIT: to clarify

on HOST there are:

webserver.DockerFile
docker-compose.yml
- html
--- index.php
--- ...
- platforms
--- dir1
--- dir2
--- dir3
--- ...
- sites-available
--- backend.conf
--- frontend.conf

inside webserver.Dockerfile there are:

RUN mkdir -p /var/www/html/backend
RUN mkdir -p /var/www/html/frontend
RUN a2ensite backend.conf frontend.conf

which does not create 'backend' and 'frontend' directories on HOST, and then fails on a2ensite, with error:

ERROR: Site backend does not exist!
ERROR: Site frontend does not exist!
ERROR: Service 'webserver' failed to build: The command '/bin/sh -c a2ensite backend.conf frontend.conf' returned a non-zero code: 1

That all indicated to me that the directories on the DOCKER that I wanted to be linked/mounted with HOST are in fact empty:

/var/www/html
/var/www/platforms
/etc/apache2/sites-available

but the directories on HOST are not empty.

Answer 1

Remember the folder to the left of the double dots is bound into the container :/var/www/html . So if the container is not checked on startup if the folder is full it will be overwritten and is empty again. You can write an Entrypoint Script which helps you with this.