502 Bad Gateway when using reverse proxy with Docker and Nginx - docker

Question

I have searched StackOverflow for my problem but I always seem to be hitting the 502 Bad Gateway with my Nginx Docker configuration. I am trying to access pgadmin4 using my domain mydomain.com/pgadmin instead of mydomain.com:8060 where 8060 is the port exposed by it's docker container. My docker-compose.yml file looks like this:
version: '3.5'
services:
reverse-proxy:
image: nginx:1.19.6
restart: always
ports:
- "80:80"
- "443:443"
postgres:
image: postgres:12
ports:
- "5432:5432"
pgadmin:
image: dpage/pgadmin4
depends_on:
- postgres
ports:
- "8060:80"
networks:
default:
external:
name: defaultnetwork
The default.conf file of my nginx container looks like this:
upstream pgadmin {
server 127.0.0.1:8060;
}
server {
listen 80;
listen [::]:80;
server_name mydomain.com;
root /usr/share/nginx/html;
index index.html index.htm;
location /pgadmin {
proxy_pass http://pgadmin;
}
}
With this configuration, I keep getting the 502 Bad Gateway error. Could someone kindly point to me where I am going wrong. I would really appreciate it.
Thanks.
[EDIT]
This is from the docker logs:
2021/02/03 08:07:42 [error] 23#23: *2 connect() failed (111: Connection refused) while connecting to upstream, client: ***.***.***.***, server: mydomain.com, request: "GET /pgadmin HTTP/1.1", upstream: "http://127.0.0.1:8082/pgadmin", host: "mydomain.com"

Answer 1

The 502 problem comes from the loopback IP here:
upstream pgadmin {
server 127.0.0.1:8060;
}
127.0.0.1 or localhost for the NGINX container is the NGINX container itself. You should use the name of the service instead:
upstream pgadmin {
server pgadmin:8060;
}
Name of the service comes from the docker-compose.yml:
services:
pgadmin: # <- this
image: dpage/pgadmin4
If you hit 404 after these changes, this is because you have to change base path of the application. Try using this config:
location /pgadmin/ {
proxy_set_header X-Script-Name /pgadmin;
proxy_set_header Host $host;
proxy_pass http://pgadmin;
proxy_redirect off;
}

Answer 2

Since your containers are working in the same network, you should access the Pgadmin container via 80th port from your Nginx container.
You should replace this line server 127.0.0.1:8060 with server pgadmin:80 in your Nginx config.