NGINX Proxy Manager UI Down - host not found in upstream

NGINX is used all kind of reverse proxy uses from Keycloak to Oracle APEX Reverse Proxy Management for self-hosting and the Autonomous DB.

I’ve had this problem couple of times now. It occurred when I took a container offline, and NPM wouldn’t start at all. I should’ve written this down the first time this happened… although here is a fix.

To get more information, request the logs

docker logs nginx-proxy-manager

Here you can see an upstream issue at line 54 of /data/nginx/proxy_host/2.conf

❯ Starting nginx ...
nginx: [emerg] host not found in upstream "opc-keycloak-1" in /data/nginx/proxy_host/2.conf:54
[12/19/2024] [1:30:06 PM] [Migrate  ] › ℹ  info      Current database version: none
[12/19/2024] [1:30:06 PM] [Setup    ] › ℹ  info      Logrotate Timer initialized
[12/19/2024] [1:30:06 PM] [Setup    ] › ℹ  info      Logrotate completed.
[12/19/2024] [1:30:06 PM] [IP Ranges] › ℹ  info      Fetching IP Ranges from online services...
[12/19/2024] [1:30:06 PM] [IP Ranges] › ℹ  info      Fetching https://ip-ranges.amazonaws.com/ip-ranges.json
[12/19/2024] [1:30:06 PM] [IP Ranges] › ℹ  info      Fetching https://www.cloudflare.com/ips-v4
[12/19/2024] [1:30:06 PM] [IP Ranges] › ℹ  info      Fetching https://www.cloudflare.com/ips-v6
[12/19/2024] [1:30:06 PM] [SSL      ] › ℹ  info      Let's Encrypt Renewal Timer initialized
[12/19/2024] [1:30:06 PM] [SSL      ] › ℹ  info      Renewing SSL certs close to expiry...
[12/19/2024] [1:30:06 PM] [IP Ranges] › ℹ  info      IP Ranges Renewal Timer initialized
[12/19/2024] [1:30:06 PM] [Global   ] › ℹ  info      Backend PID 170 listening on port 3000 ...
❯ Starting nginx ...
nginx: [emerg] host not found in upstream "opc-keycloak-1" in /data/nginx/proxy_host/2.conf:54
❯ Starting nginx ...
nginx: [emerg] host not found in upstream "opc-keycloak-1" in /data/nginx/proxy_host/2.conf:54
❯ Starting nginx ...
nginx: [emerg] host not found in upstream "opc-keycloak-1" in /data/nginx/proxy_host/2.conf:54
❯ Starting nginx ...
nginx: [emerg] host not found in upstream "opc-keycloak-1" in /data/nginx/proxy_host/2.conf:54

To workaround this temporarily, the fix is… enter bash

docker exec -it nginx-proxy-manager /bin/bash

Install nano

apt update
apt install nano

Edit the offending file

nano /data/nginx/proxy_host/2.conf

Around line 54, change

   proxy_pass       http://opc-keycloak-1:8080;

to

   proxy_pass       http://localhost:8080;

Reload nginx

nginx -s reload

Back in the game!

Once the UI is open, you can correct the hostname in the UI

ENJOY

What’s the picture? - A Fruit Tea Loaf from The Secret Bakery. Visit Yorkshire!