docker-compose Nextcloud Instance behind reverse proxy Bad gateway 502 - docker

Question

I want to switch from using the docker run-command to a docker-compose file with my nextcloud instance that runs behind a reverse proxy (jwilder/nginx-proxy).
This is the run command I used to use:
sudo docker run -d -p 8080:80 --expose 80 --expose 443 -e VIRTUAL_HOST=nextcloud.example.com -v nextcloud:/var/www/html --restart=always --name=nextcloud nextcloud:24.0.8
I installed the mariaDB later in the container so that I didn't have to struggle with networking. Also I use the Port 8080 only in my internal network for fast up- and downloading.
This worked quite well, but now I want to create a similar environment with docker-compose:
version: '3.8'
volumes:
nextcloud:
db:
services:
db:
image: mariadb:10.5
restart: always
command: --transaction-isolation=READ-COMMITTED --binlog-format=ROW
volumes:
- db:/var/lib/mysql
environment:
- MYSQL_ROOT_PASSWORD=my-super-strong-password
- MYSQL_PASSWORD=my-other-super-strong-password
- MYSQL_DATABASE=nextcloud
- MYSQL_USER=nextcloud
app:
image: nextcloud:24.0.8
restart: always
ports:
- 8080:80
expose:
- 80
- 443
links:
- db
volumes:
- nextcloud:/var/www/html
environment:
- MYSQL_PASSWORD=my-other-super-strong-password
- MYSQL_DATABASE=nextcloud
- MYSQL_USER=nextcloud
- MYSQL_HOST=db
- PHP_MEMORY_LIMIT=1G
- PHP_UPLOAD_LIMIT=128M
- VIRTUAL_HOST=nextcloud.example.com
The containers are starting successfully and I can use nextcloud in my internal network. But I cannot reach them from my domain. Instead I get a 502 Bad request. The VIRTUAL_HOST redirection seems to work since I'd get a 503 Service Temporarily Unavailable instead.
I think exposing the ports 80 and 443 doesn't work.
I've tried to add a proxy network:
networks:
proxy:
driver: bridge
external: true
and added
networks:
- default
to the db service and
networks:
- default
- proxy
to the app service.
That didn't fixed the problem. Does any of you have an idea what I can try next?
I've tried different ways to expose the ports and tried to create different networks

Answer 1

Nevermind found the problem.
Instead of simply creating an network named proxy, I had to create a new jwilder reverse-proxy service via docker compose with a name, as an example myreverseproxy. In each service I want to make public I needed to name this proxy as:
networks:
- default
- myreverseproxy
Also I had to use the name in the networks service area:
networks:
myreverseproxy:
external: true