We replaced our data pipeline with zero downtime by addressing the in-flight and post-flight problem, optimizing for high write throughput and read throughput, shared ownership, scaling limitations of a single MySQL cluster, and choosing what to fix. We solved these issues by splitting the data into separate stores, using sharding, and implementing services between clients and databases. The rollout was planned in multiple phases with minimal risk, utilizing tools like Shadow and Account Flags. By making slow and steady progress, we ensured the new system was stable and reliable, avoiding major problems and delivering a successful outcome.