<ul data-eligibleForWebStory="true"><li>Legacy systems pose challenges like risks of breaking, unclear processes, and difficulty in making changes.</li><li>Migrating to event sourcing from legacy systems doesn't require a complete rewrite.</li><li>The migration guide involves moving a 500-table Rails monolith to event sourcing incrementally.</li><li>Phase 1 involves identifying pain points like audit-heavy domains and adding event publishing to legacy code.</li><li>Phase 2 includes implementing a dual-write architecture by building parallel projections and gradually shifting reads.</li><li>Phase 3 focuses on replacing writes with commands, retiring legacy code, and handling migration pitfalls like event schema changes and performance regressions.</li><li>Key steps include laying the foundation, implementing a dual-write architecture, the big flip to replace writes, and retiring legacy code.</li><li>Migration pitfalls include event schema changes, projection drift, and performance regressions.</li><li>The guide suggests aborting migration if the team lacks event-sourcing experience, faces resistance to incremental migration, or expects a quick rewrite.</li></ul>

From Legacy to Event-Sourced: A Step-by-Step Migration Guide

Discover more