Troubleshooting Nginx Multi-Domain App: Resolving Too Many Redirects Error on Linux

A Linux Nginx redirect-loop checklist for multi-domain applications, focused on server blocks, proxy headers, app URL settings, cookie scope, cache layers, and log validation.

Quick Read

Symptom: A Linux Nginx redirect-loop checklist for multi-domain applications, focused on server blocks, proxy headers, app URL settings, cookie scope, cache layers, and log validation.
Check first: Verify Nginx configuration for each domain.
Risk: Changes system state

Symptoms

Users are encountering a 'Too Many Redirects' error when attempting to log in to a multi-domain application hosted on Nginx.

Environment

Nginx web server configured on a Linux server, serving multiple domains with a shared backend application.

Most Likely Causes

Misconfiguration in Nginx server blocks, incorrect application URL settings, or session handling issues.

What to Check First

Verify Nginx configuration for each domain.
Check application URL settings in the backend.
Inspect session handling and cookie settings.

Fix Steps

Check Nginx configuration for each domain.
Ensure that the server blocks for each domain are correctly set up to avoid redirect loops.
Safe to run: read-only
```
sudo nginx -t
```
Review the server block settings for each domain.
Look for conflicting rewrite rules or incorrect root paths that may cause redirection issues.
Example pattern only. Adjust for your environment before running.
```
cat /etc/nginx/sites-available/*
```
Check application URL settings in the backend.
Ensure that the application is configured to recognize the correct domain URLs.
Example pattern only. Adjust for your environment before running.
```
grep 'APP_URL' /path/to/application/.env
```
Inspect session handling and cookie settings.
Verify that session cookies are set correctly and not causing conflicts across domains.
Example pattern only. Adjust for your environment before running.
```
cat /path/to/application/config/session.php
```
Restart Nginx to apply any configuration changes.
Restart the Nginx service to ensure that all configuration changes take effect.
Changes system state: review before running
```
sudo systemctl restart nginx
```

Validation

Attempt to log in to the application after making changes.
Monitor for any further redirect errors.

Logs to Check

/var/log/nginx/error.log
/var/log/nginx/access.log

Rollback and Escalation

Restore previous Nginx configurations from backup.
Revert application settings to previous state.

Escalate When

If the issue persists after following all steps.
If new errors appear in the logs that are unrelated to the original problem.

Edge Cases

Check for any caching mechanisms (e.g., Cloudflare) that may be causing redirects.
Ensure that SSL settings are correctly configured if using HTTPS.

Notes from the Field

Always back up configuration files before making changes.
Document any changes made for future reference.