A practical account of rewriting a critical trading order validation system at Groww without any downtime. The approach covers four key phases: adopting empathy toward legacy code, scoping tightly with stakeholder buy-in, using shadow mode and traffic reconciliation to verify behavior before cutover, and rolling out gradually with aggressive monitoring and a robust feature-flag-based rollback plan. The rewrite achieved a 37% latency reduction, 10% fewer errors, zero downtime, and surfaced four previously unknown bugs.
Table of contents
1. Empathy, Not Blame2. Scope and Plan, But Do It Fast!3. Recon, Recon, ReconGet Groww Engineering Team ’s stories in your inbox4. Roll Out Slowly, Monitor AggressivelyThe Rollout StrategyThe Rollback PlanResults and Closing ThoughtsSort: