Amazon ElastiCache for Redis now supports online migration from self-managed Redis clusters to ElastiCache for Redis clusters running in cluster mode. Online migration simplifies moving data from self-managed Redis clusters to ElastiCache with minimal application disruption. During the migration, ElastiCache replicates cache data from each self-managed Redis source shard to the target ElastiCache cluster. Once initial replication is complete, the two clusters will be kept in sync until you are ready to update your application configuration to use ElastiCache.
Source:: Amazon AWS