Add troubleshooting/bad-gateway-gitea.md

troubleshooting/bad-gateway-gitea.md

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+# Gitea Bad Gateway Error
+
+## Problem
+
+After creating a proxy host for Gitea in Nginx Proxy Manager, visiting:
+
+```text
+https://git.casko.dev
+```
+
+resulted in:
+
+```text
+502 Bad Gateway
+```
+
+## Environment
+
+* Hetzner Cloud Server
+* Ubuntu 24.04
+* Docker
+* Gitea
+* Nginx Proxy Manager
+
+## Cause
+
+Nginx Proxy Manager could not communicate with the Gitea container.
+
+The proxy host was configured to forward traffic to:
+
+```text
+95.216.204.54:3000
+```
+
+Instead of the Docker container name.
+
+Containers on the same Docker network should communicate using container names, not the server's public IP address.
+
+## Investigation
+
+Verified Gitea was running:
+
+```bash
+docker ps
+```
+
+Verified Gitea was accessible directly:
+
+```text
+http://95.216.204.54:3000
+```
+
+Nginx Proxy Manager still returned a 502 error.
+
+## Fix
+
+Updated the proxy host settings.
+
+### Before
+
+Forward Hostname:
+
+```text
+95.216.204.54
+```
+
+Forward Port:
+
+```text
+3000
+```
+
+### After
+
+Forward Hostname:
+
+```text
+gitea
+```
+
+Forward Port:
+
+```text
+3000
+```
+
+Saved the proxy host configuration.
+
+## Result
+
+The proxy host immediately began working.
+
+The following URL became accessible:
+
+```text
+https://git.casko.dev
+```
+
+SSL certificates continued functioning correctly.
+
+## Lessons Learned
+
+When Docker containers share a network:
+
+* Use container names
+* Avoid public IP addresses
+* Verify container names with:
+
+```bash
+docker ps
+```
+
+Docker's internal DNS automatically resolves container names.