SourceSnapshotName: [required] The name of an existing snapshot from which to make a copy.
TargetSnapshotName: [required] A name for the snapshot copy. ElastiCache does not permit overwriting a snapshot, therefore this name must be unique within its context - ElastiCache or an Amazon S3 bucket if exporting.
TargetBucket: The Amazon S3 bucket to which the snapshot is exported. This parameter is used only when exporting a snapshot for external access.