legacy-modernizer
Incremental migration strategies, dependency mapping, and facade designs for safely modernizing legacy systems.
- Guides five-step workflow: assess system, plan migration, build safety net with characterization tests, migrate incrementally via strangler fig pattern with feature flags, and validate before retiring legacy code
- Includes reference templates for strangler fig facades, feature flag wrappers, and characterization test patterns to capture existing behavior as a golden master
- Enforces zero production disruption through explicit rollback triggers, traffic increment validation (5% → 25% → 50% → 100%), and one-release-cycle stability proof before legacy code removal
- Provides assessment templates, dependency mapping guidance, and monitoring setup instructions to document risks and preserve business logic throughout migration
Legacy Modernizer
Core Workflow
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Assess system — Analyze codebase, dependencies, risks, and business constraints. Produce a dependency map and risk register before proceeding.
- Validation checkpoint: Confirm all external integrations and data contracts are documented before moving to step 2.
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Plan migration — Design an incremental roadmap with explicit rollback strategies per phase. Reference
references/system-assessment.mdfor code analysis templates.- Validation checkpoint: Confirm each phase has a defined rollback trigger and owner.
-
Build safety net — Create characterization tests and monitoring before touching production code. Target 80%+ coverage of existing behavior.
- Validation checkpoint: Run the characterization test suite and confirm it passes green on the unmodified legacy system before proceeding.
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Migrate incrementally — Apply strangler fig pattern with feature flags. Route traffic via a facade; shift load gradually.
- Validation checkpoint: Verify error rates and latency metrics remain within baseline thresholds after each traffic increment (e.g., 5% → 25% → 50% → 100%).
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Validate & iterate — Run full test suite, review monitoring dashboards, and confirm business behavior is preserved before retiring legacy code.
- Validation checkpoint: New code must be proven stable at 100% traffic for at least one release cycle before legacy path is removed.
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