Step 09 of 9 2-3 weeks· advanced
Step 9: Cutover and Decommission
Turn off the legacy system. By this point traffic should already be zero — this phase is the formal teardown plus the post-migration write-up.
Recommended prompts
Use one of these to do the work in your IDE
Open the template to read it in full. Click Copy prompt to grab it (with your stack values pre-filled where they apply) — then paste into Claude Code, Cursor, or wherever you build.
Recommended skills
Drop these into Claude Code for this phase
Skills auto-trigger on the right kind of request. Install once; they apply to every prompt that fits.
Recommended MCP configs
Wire these tools into Claude Code first
MCP servers give Claude Code direct access to external systems (Jira, browsers, databases). Configure once.
When you're done
Verify these in your own work before moving on
This is a checklist for you to mentally tick off in your repo and IDE — the site doesn't track it, you do.
- Legacy traffic = 0% for 30 consecutive days
- No critical alerts from legacy in that window
- All scheduled jobs migrated
- All integrations updated to point at the new system
- DNS / proxy routes to legacy removed
- Legacy infrastructure decommissioned (compute, DB, etc.)
- Legacy code archived (don't delete; archive)
- Post-migration retrospective completed
- Lessons documented for future migrations
- Team celebration
Common pitfalls
What goes wrong at this step
- Decommissioning too fast — keep legacy in cold standby for 30+ days post-cutover
- Forgetting integrations — the partner still calling legacy; the report tool still pointing at the legacy DB
- No retrospective — the next migration won't benefit from this one's lessons
- No celebration — the team did hard work; recognize it