Migrating Sylius to a newer version is critical to benefit from the latest features, performance boosts, and security patches. For a risk-free transition, follow this 10-step methodical approach:

• Change Assessment: Review the Release Notes and the UPGRADE.md file for the new version to anticipate breaking changes.
• Full Backup: Before any changes, perform a full snapshot of your database, configuration files, and media assets.
• Staging Environment: Never work directly on production. Use an isolated environment (Docker, DDEV) to simulate the migration process.
• Dependency Updates: Adjust your composer.json and update Symfony as well as third-party bundles to compatible versions.
• Customization Audit: Check your overrides (templates, services, entities). As Sylius evolves, some of your custom code might have become native or obsolete.
• Code Refactoring: Adapt your code to new APIs or deprecations identified in your application logs.
• Database Migrations: Handle schema changes using Doctrine Migrations to ensure the integrity of your existing data.
• Regression Testing: Run your PHPUnit and Behat suites. Manually test the checkout process and payment flows.
• Planned Deployment: Schedule a maintenance window for production deployment, ideally during low-traffic periods.
• Post-Migration Monitoring: Keep a close eye on your logs (Sentry, PHP/Symfony logs) during the first few hours to catch any unexpected behavior.

By following this rigorous protocol, you minimize downtime and ensure the long-term stability of your e-commerce platform.