Zero-Downtime PHP 8.4 Migration on Live Infrastructure
Challenge
Migrating production infrastructure to PHP 8.4 while maintaining full compatibility with both a Laravel 13 application and a CodeIgniter 3 legacy codebase, plus third-party packages that had not been updated for PHP 8.4.
Approach
Staged migration using parallel PHP-FPM pools — four PHP versions (7.4, 8.1, 8.2, 8.4) running simultaneously on the same server, with traffic routed per virtual host. Identified all breaking changes before cutover to production.
Implementation
Fixed Guzzle and AWS SDK compatibility issues for PHP 8.4. Resolved DOMDocument removal from default extensions. Repaired setuid PHP wrapper used in deployment scripts. Recovered git repository corruption that occurred mid-migration.
Results
Successful migration with zero downtime. Both Laravel 13 and CodeIgniter 3 now running on the same server under different PHP-FPM pools. Deployment pipeline fully restored.