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SUMMARY:Swapping the Engine Mid-Flight: Migrating a Live Decision System w
 ith Zero Behavior Change - Ankit Agarwal
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UID:pretalx-devopsdays-portland-2026-GDDBWE@talks.devopsdays.org
DESCRIPTION:We replaced the engine behind a high-traffic\, real-time decis
 ion system - while it kept running\, with no user-visible change. This is 
 the honest story of de-risking a high-stakes migration from a legacy rule 
 engine to a new platform\, and the techniques that made it survivable.\nI'
 ll walk through what actually worked: shadow/replay testing that ran old a
 nd new side-by-side on real traffic and diffed every response\; a switchab
 le flow that let us flip and instantly un-flip the traffic without a code 
 change or deployment\; automated configuration-drift detection between the
  two systems\; and a staged rollout where rollback was a designed feature\
 , not a panic button. You'll hear the decisions and tradeoffs behind each 
 choice\, the bugs that equivalence testing caught but code review missed\,
  and the things we still got wrong.\nIf you're staring down a scary migrat
 ion of something that can't go down\, you'll leave with a concrete\, reusa
 ble playbook and a more honest sense of what "zero downtime" really costs.
LOCATION:Ballroom
URL:https://talks.devopsdays.org/devopsdays-portland-2026/talk/GDDBWE/
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