Migrating Existing Datastores

This post details the migration of the Grab Identity team's authentication token cache from a single Redis node to an AWS ElastiCache cluster. The team faced challenges with scalability and a single point of failure. They evaluated options including larger Redis instances, custom Redis clusters, and AWS ElastiCache. Ultimately, they opted for a sharded ElastiCache cluster with read replicas to handle high read volumes and provisioned shards to cover future write load growth. A six-step, zero-downtime migration plan was executed using configuration flags, shadow writes, synchronous writes, asynchronous reads with validation, full read switch, and finally, decommissioning the old node. The migration was successful, achieving no downtime, zero collateral damage, and no security loopholes.