Don’t patch the old. Move to what works.

Always upgrade incrementally (8→9→10→11→12) on a staging copy first, following Laravel's official upgrade guide step‑by‑step, testing your full suite after each version. Use blue‑green deployments or feature flags to swap traffic without downtime, and lock composer dependencies to avoid surprises. The rationale: gradual changes let you catch issues early, and parallel environments ensure business continuity.

Common pitfalls include PHP 8.2+ strictness breaking old code, Sanctum 4 auth changes, and package incompatibilities—run phpstan/rector beforehand to surface them. Breaking changes often hit Eloquent (enum casting), middleware signatures, and config loading. Rationale: these stem from modernizing for security/performance, so audit deps and test auth flows thoroughly before going live.

For large legacy apps, Laravel Shift automates 80% of boilerplate safely (~$500‑2K depending on size), manual is free but slow/risky for teams without deep expertise, and experts cost $10K‑50K+ but deliver polished results with warranties. Choose based on timeline and risk tolerance—Shift + manual review balances speed and control best. Rationale: automation handles syntax churn, humans own business logic.

Extract business logic into Laravel services/jobs first via a Strangler Fig pattern (new features on Laravel, proxy old endpoints), then sync data with Laravel migrations/replicators. Run both systems in parallel during cutover, monitoring for discrepancies. Rationale: this minimizes big‑bang risk, preserves proven logic, and lets you iterate toward Laravel strengths like Eloquent without data loss.

Use Laravel migrations with feature flags or DB triggers for schema changes, backfill data in batches via queued jobs, and leverage read replicas for zero‑downtime writes. Test data integrity with DB assertions in CI. Rationale: production data is sacred—phased, reversible changes ensure consistency without locking tables or risking outages.

Run static analysis (phpstan, sonar) and manual code reviews to map legacy patterns to modern ones: replace raw queries with Eloquent scopes/relationships, procedural code with queued jobs/events, and fat controllers with thin actions/services. Prioritize high‑traffic paths first. Rationale: auditing uncovers tech debt while refactoring unlocks scalability and maintainability Laravel excels at.