4.2M links migrated over one weekend

Overtone had eight years of transactional email in the wild, every message carrying short links on a domain their previous vendor controlled. Leaving meant either keeping that contract forever or breaking history.

Same paths, new owner

Trace imported all 4.2 million links with their existing paths and served them from Overtone's own domain on the Friday. Because the paths were preserved, an email from 2019 resolves exactly as it did before — the difference is that Overtone now owns the redirect.

The engineering view

• Median redirect 31ms at the edge, against 240ms before
• Bulk creation through one API call rather than a queue of thousands
• Click events streamed into their warehouse, joined on their own order IDs

The migration ran on a Saturday with a two-engineer rollback plan that was never used.