So You've Decided to Do a Technical Migration
summary
Monzo migrates its monorepo from Flow to TypeScript over just over two years, moving incrementally with volunteers then company-wide teams. Engineers build a package generator and a TypeScript migration script plus a dependency‑ready script, track progress with a migration dashboard and milestones, and set roll back guard rails for incidents. The migration exposes many hidden type bugs, speeds compiles and VSCode, required scope reduction and careful stakeholder buy‑in, and ultimately succeeds (Babel removal in December proves it works).
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chapters (13)
- 0:00Introduction and context
- 2:45Why Monzo migrated to TypeScript
- 5:10Starting the migration process
- 9:12Incremental vs big bang migration
- 12:43Measuring progress and milestones
- 15:20Setting deadlines and managing scope
- 19:16Risks of pausing migrations
- 21:38Handling incidents during migration
- 24:27Rollback plans and guardrails
- 26:50Celebrating the migration success
- 28:02Do you need the migration?
- 35:26Choosing boring technology
- 36:32Q&A session
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