ElastiCache

A node is the smallest buidling block of an ElastiCache deployment. Each node has its own DNS name and port.

Both Redis and Memcached cluster need to be run in a VPC, a collection of subnets within that VPC.

Redis

A Redis shard is a grouping of one to six related nodes. Redis clusters can have up to 500 shards, with data partitioned across the shards.

Redis Repliation happens in a shard where one of the nodes is the read/write primary node. All the other nodes are read-only replica nodes. Locating read replicas in multiple Availibility Zones improves fault tolerance.

The primary endpoint of a Redis cluster is a DNS name that always resolves to the primary node in the cluster. The primary endpoint is immune to changes to the cluster, such as promoting a read replica to the primary role. Note that Read Replica failover or promotion is happened automatically which is different to RDS (non-Aurora) database.

The reader endpoint of a Redis cluster will evenly split incoming connections to the endpoint between all read replicas in a ElastiCache for Redis cluster.

In addition, you can use global datastores to create cross-region read replica clusters for ElastiCache for Redis to enable low-latency reads and disaster recovery across AWS Regions.

AUTH

Redis AUTH can only be enabled for encryption in-transit enabled ElastiCache for Redis clusters.

Memchached

A Memcached cluster is a logical grouping of one or more ElastiCache nodes. Data is partitioned across the nodes in the Memcached cluster. A Memcached cluster can have up to 300 nodes. And nodes can be run across multiple Availibility Zones.

A Memcached cluster does not have the concept of sharding as Redis. Memcached cluster relies on the client Auto-Discovery to automatically identify all of the nodes in a cached cluster, and to initiate and maitain connetions to all of these nodes.

Comparing between Redis and Memecached

https://aws.amazon.com/elasticache/redis-vs-memcached/

Read More

• Elasticache Redis
• Elasticache Memcached