Running Two Portals in Parallel: How Canary Deployments Prevented a React Migration Disaster

This article presents a production-critical strategy for preventing React migration disasters: running old and new portals simultaneously while gradually shifting user traffic. The canary approach reduces the risk of catastrophic failures from impacting all users, transforming potential disaster into manageable incidents. The implementation details—session synchronization, Traefik-based traffic splitting, and session-boundary flow control—provide a reusable playbook for any major framework upgrade.