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Plan a legacy framework migration with a reversible, staged rollout
⁂auto-checked, 3 hours oldAauraNovice
The prompt
I need to migrate codebase_description from old_framework to new_framework. Produce a migration plan, not code, structured as:
1. Inventory: what categories of code/config depend on the old framework's specific behavior (not just imports, actual behavioral coupling like implicit type coercion, routing conventions, middleware order).
2. Strangler-fig staging: an order of migration that lets old and new run side by side, with the riskiest, most-coupled piece migrated last, not first.
3. For each stage, a concrete rollback trigger (a metric or error class, not 'if it feels wrong') and how to revert that stage specifically without reverting the whole migration.
4. Testing strategy per stage: what must have parity tests before cutover versus what can be verified by monitoring after.
5. A list of behavioral differences between old_framework and new_framework that commonly cause silent bugs during this exact migration, so I know what to watch for.
Do not recommend a big-bang rewrite unless you can justify why staging is not possible here.
Where it has been run
| Model | Version | People | Broke | Auto | Last |
|---|---|---|---|---|---|
| Claude | Haiku 4.5 | 0 | 0 | 1/1 | 3 hours ago |
Example output
Stage order: (1) migrate stateless utility/formatting code with pure unit test parity, (2) migrate leaf API routes with no shared middleware, (3) migrate the auth middleware last since every route depends on its side effects and its error-handling order differs subtly between frameworks.
Rollback trigger for stage 3: 5xx rate on auth-gated routes exceeds 0.5% over a 10-minute window, or session-cookie parse errors appear in logs; revert by re-pointing the router's auth middleware slot back to the old implementation via the feature flag `auth_impl`, without touching stages 1-2.
Known silent-bug source: {{old_framework}} treats an empty string as falsy in route guards, {{new_framework}} treats it as truthy; this has bitten teams doing this exact migration when a guard like `if (!req.query.id)` silently stops working as expected.
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