AWS Storage Options – CloudFront & ElastiCache

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Amazon CloudFront

  • is a webservice for content delivery
  • provides low latency by caching and delivering content from a global network of edge locations located nearest to the user
  • supports both HTTP to allows static, dynamic content and Real Time Messaging Protocol (RTMP) for streaming of videos
  • optimized to work as with Amazon services like S3, ELB etc. as well as works seamlessly with any non-AWS origin server

Ideal Usage Patterns

  • is ideal for distribution of frequently accessed static content, or dynamic content or for streaming audio or video that benefits from edge delivery

Anti-Pattern

  • Infrequently accessed data
    • If the data is infrequently accessed, it would be better to serve the data from the Origin server
  • Programmatic cache invalidation
    • CloudFront supports cache invalidation, however AWS recommends using object versioning rather than programmatic cache invalidation.

Performance

  • is designed for low latency and high bandwidth delivery of content by redirecting the user to the nearest edge location in terms of latency and caching the content preventing the round trip to the origin server

Durability & Availability

  • provides high Availability by delivering content from a distributed global network of edge locations. Amazon also constantly monitors the network paths connecting Origin servers to CloudFront
  • does not provide durable storage, which is more of the responsibility of the underlying Origin server providing the content for e.g. S3

Cost Model

  • has two pricing components:
    • regional data transfer out (per GB) and
    • requests (per 10,000)

Scalability & Elasticity

  • provides seamless scalability & elasticity by automatically responding to the increase or the decrease in the demand

ElastiCache

  • is a webservice that makes it easy to deploy, operate, and scale a distributed, in-memory cache in the cloud
  • helps improves performance of the applications by allowing retrieval of data from fast, managed, in-memory caching system
  • supports Memcached (object caching) & Redis (key value store that supports data structure) open source caching engines

Ideal Usage Patterns

  • improving application performance by storing critical data in-memory for low latency access
  • use cases involve usage as a database front end for read heavy applications, improving performance and reducing load on databases, or managing user session data, cache dynamically generated pages, or compute intensive calculations etc.

Anti-Patterns

  • Persistent Data
    • If the application needs fast access to data coupled with strong data durability, Amazon DynamoDB would be a better option

Performance

  • Although ElastiCache provides low latency access to the data, the performance depends on the caching strategy and the hit ratio at the application level

Durability & Availability

  • stores transient data or transient copies of durable data, so the data durability is managed by the source
  • With the Memcached engine
    • all ElastiCache nodes in a single cache cluster are provisioned in a single Availability Zone.
    • ElastiCache automatically monitors the health of your cache nodes and replaces them in the event of network partitioning, host hardware, or software failure.
    • In the event of cache node failure, the cluster remains available, but performance may be reduced due to time needed to repopulate the cache in the new “cold” cache nodes.
    • To provide enhanced fault-tolerance for Availability Zone failures or cold-cache effects, you can run redundant cache clusters in different Availability Zones.
  • With the Redis engine,
    • ElastiCache supports replication to up to five read replicas for scaling. To improve availability, you can place read replicas in other Availability Zones.
    • ElastiCache monitors the primary node, and if the node becomes unavailable, ElastiCache will repair or replace the primary node if possible, using the same DNS name.
    • If the primary cache node recovery fails or its Availability Zone is unavailable, primary node can be failed over to one of the read replicas with an API call.

Cost Model

  • has a single pricing component:
    • pricing is per cache node-hour consumed

Scalability & Elasticity

  • ElastiCache is highly scalable and elastic.
  • Cache node can be added or deleted to the cache cluster
  • Auto Discovery enables automatic discovery of Memcached cache nodes by ElastiCache Clients when the nodes are added to or removed from an ElastiCache cluster.

 

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