preferredAvailabilityZones

A list of PreferredAvailabilityZone strings that specify which availability zones the replication group's nodes are to be in. The nummber of PreferredAvailabilityZone values must equal the value of NewReplicaCount plus 1 to account for the primary node. If this member of ReplicaConfiguration is omitted, ElastiCache selects the availability zone for each of the replicas.