To address the root causes identified, follow these steps to potentially fix the "500 Internal Server Error" in your NGINX reverse proxy setup:
Verify Backend Service:
Ensure the Docker container for your backend service (e.g., Nextcloud) is running and accessible at 10.0.100.6:8080. Use curl http://10.0.100.6:8080 or access this URL from a browser on the same network to confirm.
Correct NGINX Configuration:
Update the proxy_pass directive to match the exact endpoint of your backend service. If the service is directly at 10.0.100.6:8080, use proxy_pass http://10.0.100.6:8080; without a trailing slash.
Ensure the rest of the proxy settings are correct and compatible with your backend service requirements.
SELinux Configuration:
Temporarily set SELinux to permissive mode with sudo setenforce 0 and retry accessing the service. If this fixes the issue, use the audit2allow tool to analyze SELinux logs and create a new policy module to allow the required connections, instead of leaving SELinux disabled.
Adjust Firewall Settings:
Check and adjust your firewall settings to allow traffic from NGINX to your Docker containers. If using firewall-cmd, you might need to add a rule to allow connections to the specific port your backend service is running on.
Review NGINX Logs:
Check /var/log/nginx/error.log for specific error messages that could indicate the exact problem. Address any errors or warnings found here.
Reload NGINX Configuration:
After making changes to your NGINX configuration, reload the service to apply the changes. Use sudo nginx -t to test the configuration for syntax errors, then sudo systemctl reload nginx to apply changes.