Amazon ElastiCache

What is Amazon ElastiCache?

ElastiCache is a fully managed in-memory data store. It significantly improves latency and performance for all read-heavy application workloads. In-memory caches are faster than disk-based databases. It works with both Redis and Memcached protocol based engines.

Features:

● It is high availability as even the data center is under maintenance or outage; the data is still retrieved from Cache.

● Unlike databases, data is retrieved in a key-value pair fashion.

● Data is stored in nodes which is a unit of network-attached RAM. Each node has its own Redis or Memcached protocol running. Automatic replacement of failed nodes is configured.

● Memcached features –

○ Data is volatile.

○ Supports only simple data-type.

○ Supports multi-threading.

○ Scaling can be done by adding or removing nodes.

○ Nodes can span in different Availability Zones.

○ Multi-AZ failover is not supported.

● Redis features –

○ Data is non-volatile.

○ Supports complex Data types like strings, hashes, and

geospatial-indexes.

○ Doesn’t support multi-threading.

○ Scaling can be done by adding shards and not nodes. A shard is a collection of primary nodes and read-replicas.

○ Multi-AZ is possible by placing a read replica in another AZ.

○ In case of failover, can be switched to read replica in another AZ

Best practices:

● Storing web sessions. In web applications running behind a load balancer, use Redis so if one the server is lost, data can still be retrieved.

● Caching Database results. Use Memcached in front of any RDS where repetitive queries are being fired to improve latency and performance.

● Live Polling and gaming dashboards. Store frequently accessed data in Memcached to fetch results quickly.

● Combination of RDS and Elasticache can be utilized to improve architecture on the backend.

Pricing:

● Available only for on-demand and reserved nodes.

● Charged for per node hour.

● Partial node hours will be charged as full node hours.

● No charge for data exchange between Elasticache and EC2 within the same

AZ. https://aws.amazon.com/elasticache/pricing/