502 Bad Gateway when using reverse proxy with Docker and Nginx

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"

anemyte · Accepted Answer · 2022-01-10 06:42:38Z

6

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;
    }

edited Jan 10, 2022 at 6:42

answered Feb 3, 2021 at 8:42

anemyte

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4 Comments

realnsleo Over a year ago

Thanks @anemyte for this. I am one step closer. From the logs I can see that nginx correctly resolves the container's IP address. But the request looks like this: GET /pgadmin HTTP/1.1", upstream: "http://172.18.0.6:8082/pgadmin instead of this: GET /pgadmin HTTP/1.1", upstream: "http://172.18.0.6:8082. How can I fix this?

anemyte Over a year ago

@realnsleo it works on port 80 by default, so you shouldn't specify port unless you've changed it in pgadmin config. That is just proxy_pass http://pgadmin as it was before.

realnsleo Over a year ago

Ah! Yes. Sorry. I have removed the ports from the docker-compose.yml file and I am now getting a 404 error. Any ideas?

anemyte Over a year ago

@realnsleo I've managed to dig out a solution to it in web archive. I'll update the answer.

Adil · Accepted Answer · 2021-02-03 09:08:50Z

1

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.

edited Feb 3, 2021 at 9:08

answered Feb 3, 2021 at 8:57

Adil

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