AWS Certified Solutions Architect Professional SAP-C02 Practice Question
Your company's customer-analytics platform stores 200 GiB of volatile session data in an Amazon ElastiCache for Redis replication group that is currently running in cluster mode disabled. The cluster has one primary and two replica nodes spread across two Availability Zones (AZs). Over the next six months the dataset is expected to outgrow the memory capacity of a single cache node. Reliability requirements are:
The cache must continue to accept reads and writes automatically if any single AZ becomes unavailable.
Recovery time for an AZ outage must be under 1 minute.
Application endpoints must remain unchanged during failover.
Memory overhead should be kept as low as possible while scaling for the larger dataset.
Which deployment approach best meets these requirements?
Replace Redis with a three-node Amazon ElastiCache for Memcached cluster that uses client-side hashing across three AZs.
Keep cluster mode disabled, scale up to a larger node type, add a third replica in a third AZ, and enable Multi-AZ automatic failover.
Convert the replication group to Redis cluster mode enabled with two shards and one replica per shard, distributing primaries and replicas across two AZs (Multi-AZ automatic failover enabled by default).
Schedule daily RDB snapshots to Amazon S3 and plan to restore a new cluster in another AZ when an outage occurs.
Migrating to a Redis cluster mode enabled deployment with multiple shards satisfies every requirement. Sharding splits the dataset across primaries, so each replica stores only the portion of data held by its shard; with one replica per shard, the memory footprint is roughly 2× the dataset instead of 3× in the current cluster-mode-disabled design, meeting the overhead goal. Cluster-mode-enabled replication groups have Multi-AZ automatic failover turned on by default when at least one replica in every shard resides in a different AZ, so if an AZ or primary node fails ElastiCache promotes the replica in a few seconds and propagates the same DNS endpoint, giving an RTO well below 1 minute with no code changes. The alternative options either cannot scale beyond a single-node memory limit, lack automatic failover for writes, or depend on manual restore procedures, so they fail one or more stated requirements.
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What is the difference between Redis cluster mode enabled and cluster mode disabled?
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AWS Certified Solutions Architect Professional SAP-C02
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