Legacy Codebase Migration Workflow

AI-generated Strangler Fig migration checklist covering baseline tests, adapters and incremental changes. No completed migration results are supplied.

Tags: workflow, migration, refactoring, strangler-pattern, typescript

Category: coding

Listing attribution: SimplyUtils

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Legacy Codebase Migration Workflow

Goal

Incrementally modernize legacy codebases without risky, all-at-once rewrites.

Migration Steps

1. Establish Invariant Baselines

  • Create end-to-end regression tests capturing current input/output behavior for the target module.
  • Record sample real-world inputs and expected output snapshots.

2. Build the Modern Facade / Interface

  • Define clean TypeScript interfaces for the module's public API.
  • Implement an adapter layer routing requests between legacy and modern implementations.

3. Incremental File-by-File Modernization

  • Convert files starting from the leaf dependencies (utility functions) up to top-level controllers.
  • Replace any with explicit types and runtime Zod validation.

4. Canary / Dual-Run Verification

  • Log any discrepancies between legacy output and modern output.
  • Validate performance and memory consumption under load.

5. Decommission Legacy Code

  • Remove old helper functions and adapters once 100% traffic is verified on the modern path.