Nginx reverse proxy (in Docker) to a web app (also in Docker) - docker

Question

I have set up a web application in docker which is currently running internal to the host at 172.19.0.3:8888. I want this web application accessible over the internet on port 443 (https), with requests to port 80 (HTTP) redirected to 443.
I plan to use an Nginx reverse proxy in a docker container to achieve this, but I do not know how to properly configure it to point at the docker container 172.19.0.3:8888. Accessing http://172.19.0.3:8888 from the host works.
Here is the guide I tried to follow, but it just didn't show how to point at a docker container specifically.
https://medium.com/#pentacent/nginx-and-lets-encrypt-with-docker-in-less-than-5-minutes-b4b8a60d3a71
Note
If I set the port 443 proxy_pass to http://example.org, it works. So Cert configurations are working correctly.
Web application
Running on 172.19.0.3:8888 internal to the host
docker-compose for Nginx and Certbot
My certs are coming back clean.
version: '3'
services:
nginx:
image: nginx:1.15-alpine
ports:
- "80:80"
- "443:443"
volumes:
- ./Volumes/nginx:/etc/nginx/conf.d
- ./Volumes/certbot/conf:/etc/letsencrypt
- ./Volumes/certbot/www:/var/www/certbot
certbot:
image: certbot/certbot
volumes:
- ./Volumes/certbot/conf:/etc/letsencrypt
- ./Volumes/certbot/www:/var/www/certbot
Nginx app.conf
server {
listen 80;
server_name forums.example.com;
location /.well-known/acme-challenge/ {
root /var/www/certbot;
}
location / {
return 301 https://$host$request_uri;
}
}
server {
listen 443 ssl;
server_name forums.example.com;
ssl_certificate /etc/letsencrypt/live/forums.example.com/fullchain.pem;
ssl_certificate_key /etc/letsencrypt/live/forums.example.com/privkey.pem;
include /etc/letsencrypt/options-ssl-nginx.conf;
ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem;
location / {
proxy_pass http://172.19.0.3:8888/;
}
}
Web Application
flarum:
image: mondedie/docker-flarum:0.1.0-beta.8.1-stable
container_name: flarum
env_file:
- ./flarum.env
volumes:
- ./Volumes/assets:/flarum/app/public/assets
- ./Volumes/extensions:/flarum/app/extensions
- ./Volumes/nginx:/etc/nginx/conf.d
depends_on:
- mariadb
mariadb:
image: mariadb:10.2
container_name: mariadb
environment:
- MYSQL_ROOT_PASSWORD=password
- MYSQL_DATABASE=flarum
- MYSQL_USER=flarum
- MYSQL_PASSWORD=password
volumes:
- ./Volumes/mysql/db:/var/lib/mysql

Answer 1

Docker Compose creates a seprate network for docker-compose.yaml file.
So you can add your web application as service (eg: webapp) in current compose file. And in nginx.conf directly point to your service. Rather than using IP you can use the service name as DNS which will resolve by Docker for the same network.
location / {
proxy_pass http://webapp:8888/;
}