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Financial Services

Legacy Modernisation, No Downtime

Old and new running side by side until the new path has earned the traffic. Nothing is switched on a single weekend: routes move a slice at a time, differences are investigated rather than waved through, and the previous path stays available the whole way through.

To first release
2 weeks
Downtime
0
Built with
  • Kafka
  • Go
  • Kubernetes
  • Terraform
  • Postgres

The problem

A revenue-critical monolith is expensive to change and risky to touch, but a rewrite-and-switch cutover puts the whole business on a single deploy. Neither standing still nor a big-bang rewrite is acceptable.

How we would sequence it

  1. 01Map real traffic and data flows before touching any code
  2. 02Put an event bridge between the monolith and the new services
  3. 03Route a small traffic slice to the new path and compare outputs
  4. 04Widen the slice only when parity holds under production load
  5. 05Keep the rollback switch live until the old path is decommissioned

This solution describes our method for a class of problem. It is not a record of a completed client engagement, and the figures above are scope estimates rather than measured results.

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