Basic Tier Cloud Memorystore for Redis instances experience a full cache flush during maintenance. If your application cannot withstand a full cache flush, create it with a Standard Tier instance.
Cloud Memorystore for Redis instances undergo maintenance approximately once per quarter to include the latest security patches and updates. Cloud Memorystore for Redis does not currently allow you to specify maintenance windows to indicate when maintenance updates to your Redis instance can occur.
Standard Tier instances preserve data using rolling upgrades, updating the replica first, initiating a failover, then upgrading the master. To learn more about the failover process for Redis instances, see High Availability. For more details about the difference between the Basic Tier and the Standard Tier, see Redis Tier Capabilities.