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/
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