migration-refactoring

Migration & Refactoring

Systematic approach to complex code migrations with safety guardrails and rollback capabilities.

When to Use

• Dependency upgrades - Major version bumps with breaking changes
• Framework migrations - React class→hooks, Flask→FastAPI, Django→DRF, etc.
• Language modernizations - Python 2→3, JavaScript→TypeScript
• Large-scale refactoring - Cross-file changes requiring consistency
• Database schema evolution - Migrations with data transformation
• Monorepo decomposition - Extracting services from monoliths

Core Workflow

Phase 1: Analysis

1. Identify scope - What files, modules, and dependencies are affected?
2. Map dependencies - Create a dependency graph of cross-file relationships
3. Find breaking changes - Analyze changelogs, migration guides, deprecation warnings
4. Assess risk - Flag high-risk changes (public APIs, critical paths)

Phase 2: Planning

1. Create migration plan - Ordered sequence of changes
2. Define checkpoints - Intermediate states that compile/work
3. Design rollback strategy - How to revert if issues arise
4. Estimate effort - Time and complexity assessment

Phase 3: Execution

1. Execute in phases - Apply changes incrementally
2. Validate at each checkpoint - Test compilation, run tests, verify functionality
3. Document changes - Update docs, changelogs, ADRs
4. Commit incrementally - Each checkpoint is a commit

Phase 4: Validation

1. Run full test suite - Verify nothing broken
2. Performance testing - Ensure no regressions
3. Code review - Human validation of changes
4. Production rollout - Deploy with monitoring

Migration Patterns

Pattern 1: Gradual Migration

Old API → Compatibility Layer → New API → Remove Old

When: Cannot change all call sites at once

Pattern 2: Feature Flags

if (useNewImplementation) {
  return newImplementation();
} else {
  return oldImplementation();
}