Docker compose & nginx network hostnames - docker

Question

I have the following configuration:
nginx started by a docker compose file acting as reverse proxy // ssl endpoint
an application service started by a different docker compose (for modularity reasons) file serving a application
reverse_proxy and app_service are connected via the app_network
Since they are connected via the app_network, I am able to address the app_service in the nginx configuration like http://app_service:8080, which is nice because I don't need to expose ports on the app service itself.
Unfortunately, nginx won't start until I brought up the app service container because it checks the existance of the hostname app_service upon startup.
How can I prevent nginx from checking the hostname on startup, maybe causing a Bad Gateway error when trying to connect while app_service is not running yet?
Configuration files for reference:
# reverse proxy docker-compose.yml
version: '3'
services:
reverse_proxy:
restart: always
container_name: reverse_proxy
image: nginx
ports:
- 80:80
- 443:443
volumes:
- /srv/docker/nginx/config:/etc/nginx
- /srv/ssl:/srv/ssl
networks:
default:
external:
name: app_network
# application service docker-compose.yml
version: '3'
services:
app_service:
restart: always
container_name: app_service
image: <my_app_image>
networks:
default:
external:
name: app_network
# nginx config
server {
listen 443 ssl http2;
listen [::]:443 ssl http2;
server_name app.example.com;
location / {
proxy_pass http://app_service:8080;
include proxy.conf;
}
ssl_certificate /srv/ssl/<mycert>.crt;
ssl_certificate_key /srv/ssl/<mykey>.key;
}

Answer 1

Here is a way that worked for me:
# nginx config
server {
listen 443 ssl http2;
listen [::]:443 ssl http2;
server_name app.example.com;
location / {
set $upstream app_service:8080;
proxy_pass $upstream;
include proxy.conf;
}
ssl_certificate /srv/ssl/.crt;
ssl_certificate_key /srv/ssl/.key;
}
This results in a 502 Bad Gateway message if the host is unavailable and does not check availability at startup.