Nginx 502 Bad Gateway Docker troubleshooting tips by our experts will help resolve this issue in a jiffy. 

At Bobcares, we offer solutions for every query, big and small, as a part of our Docker Hosting Support Service.

Let’s take a look at how our Support Team is ready to help customers resolve Nginx 502 bad gateway Docker error.

How to resolve Nginx 502 bad gateway docker

Some of our customers have been coming across the 502 Bad Gateway error message when they attempt to have a docker container with Nginx work as a reverse proxy. Fortunately, our Support Team has come up with several different ways to resolve this specific issue.

Troubleshooting Tips: Nginx 502 Bad Gateway 

Option 1:

1. First, we have to set the server name. This is done in different server blocks in the Nginx configuration. Our Support Techs would like to point out that we have to use the docker port rather than the host port in this scenario.

   server {
   
     listen 80;
     server_name server2048;
   
     location / {
       proxy_pass "http://server2048:8080";
     }
   
   }
   
   server {
   
     listen 80;
     server_name server1;
   
     location / {
       # We have to refer to docker port and not the host port
        proxy_pass "http://server1:8080";
     }
   
   }

   Option 2:

   If the above solution did not resolve the issue, our Support Techs recommend tuning proxy_buffer_size as seen below:

   proxy_buffering off;
   proxy_buffer_size 16k;
   proxy_busy_buffers_size 24k;
   proxy_buffers 64 4k;

   proxy_buffer_size defines how much memory Nginx will allocate for each request. This memory is put to use for reading as well as storing the HTTP headers of the response.

   Option 3:

   This solution involves declaring the external network in case the container we are pointing to is defined in a different docker-compose.yml file:

   version: "3"
   
   services:
     webserver:
       image: nginx:1.17.4-alpine
       container_name: ${PROJECT_NAME}-webserver
       depends_on:
         - drupal
       restart: unless-stopped
       ports:
         - 80:80
       volumes:
         - ./docroot:/var/www/html
         - ./nginx-conf:/etc/nginx/conf.d
         - certbot-etc:/etc/letsencrypt
       networks:
         - internal
         - my-passwords
   
   networks:
     my-passwords:
       external: true
       name: my-passwords_default
   
   nginx.conf:
   
   server {
       listen          80;
       server_name     test2.com www.test2.com;
       location / {
           proxy_pass  http://my-passwords:3000/;
       }
   }

   Option 4:

   In this solution, the localhost points to the container itself. In other words, with an upstream like the one below:

   upstream foo{
     server 127.0.0.1:8080;
   }

   or

   upstream foo{
     server 0.0.0.0:8080;
   }

   This informs Nginx to pass the request to the localhost.

   Alternatively, we can also choose to run Nginx on the same network as the host:

   docker run --name nginx -d -v /root/nginx/conf:/etc/nginx/conf.d --net=host nginx

   Furthermore, we do not have to expose any ports in this scenario.

   Last but not least, another approach to resolve the issue is to reconfigure the Nginx upstream directive in order to directly connect to the host machine via adding a remote IP address:

     upstream foo{
     //insert your hosts ip here
     server 192.168.99.100:8080;
   }

   This pushes the container to go through the network stack and thereby resolve the host correctly.

   Let us know in the comments which troubleshooting tip works for you. If you are still having trouble, drop us a line and our Support Techs will help you out in a jiffy.

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   Conclusion

   To sum up, our skilled Support Engineers at Bobcares demonstrated how to resolve Nginx 502 bad gateway docker.

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