ElastiCache

Question 1

What is ElastiCache?

Answer 1

Fully managed in-memory data store, compatible with Redis or Memcached

Question 2

What are the main features of ElastiCache?

Answer 2

really high performance and sub-millisecond latency.

Question 3

What does involve to use ElastiCache in your application?

Answer 3

heavy code changes

Question 4

What must have ElastiCache to make sure only the most current data is used?

Answer 4

an invalidation strategy

Question 5

How does work the mechanism among Applications - ElastiCache - RDS?

Answer 5

Applications queries ElastiCache, if not available, get from RDS and store in ElastiCache

Question 6

What is a common use case for ElastiCache?

Answer 6

To save User Session Store

Question 7

What is distinctive on ElastiCache Memcached?

Answer 7

sharding, non persistent, no backup and restore, multithreading

Question 8

What is distinctive on ElastiCache Redis?

Answer 8

Multi AZ with failover, read replicas, data durability using AOF, backup and restore

Question 9

How can you use IAM authentication for ElastiCache?

Answer 9

ElastiCache does not support it

Question 10

In terms of security what does ElastiCache support?

Answer 10

SSL in flight encryption

Question 11

How are IAM policies used on ElastiCache?

Answer 11

only for API-level security

Question 12

What does Redis provide for extra security of ElastiCache?

Answer 12

Redis AUTH, a password/token when you create a Redis cluster on top of SGs

Question 13

What does Memcached provide for extra security of ElastiCache?

Answer 13

Supports SASL-based authentication (advanced)

Simple Authentication and Security Layer

Question 14

What are the patterns for ElastiCache?

Answer 14

• Lazy Loading / Cache-Aside / Lazy Population
• Write Through
• Session Store

Question 15

What is ElastiCache’s Lazy Loading / Cache-Aside / Lazy Population pattern?

Answer 15

It is the known pattern

Question 16

What is ElastiCache’s Write Through pattern?

Answer 16

Adds or update data in the cache when written to a DB (no stale data)

Question 17

What is ElastiCache’s Session Store pattern?

Answer 17

store temporary session data in a cache (using TTL features)

Question 18

What are the pros of ElastiCache’s Lazy Loading / Cache-Aside / Lazy Population pattern?

Answer 18

• Only requested data is cached (the cache isn’t filled up with unused data)
• Node failures are not fatal (just increased latency to
  warm the cache)

Question 19

What are the cons of ElastiCache’s Lazy Loading / Cache-Aside / Lazy Population pattern?

Answer 19

• Cache miss penalty that results in 3 round trips, noticeable delay for that request
• Stale data: data can be updated in the database and outdated in the cache

Question 20

What are the pros of ElastiCache’s Write Through pattern?

Answer 20

• Data in cache is never stale, reads are quick

- Write penalty vs Read penalty (each write requires 2 calls)

Question 21

What are the cons of ElastiCache’s Write Through pattern?

Answer 21

• Missing Data until it is added / updated in the DB. Mitigation is to implement Lazy Loading strategy as well
• Cache churn – a lot of the data will never be read

Question 22

How can occur ElastiCache’s Cache eviction?

Answer 22

In three ways:
• You delete the item explicitly in the cache
• Item is evicted because the memory is full and it’s not recently used (LRU)
• You set an item time-to-live (or TTL)

Question 23

For what kind of data are helpful ElastiCache’s TTL?

Answer 23

TTL are helpful for any kind of data:
• Leaderboards
• Comments
• Activity streams

Question 24

What to do if too many ElastiCache’s evictions happen due to memory

Answer 24

you should scale up or out

Question 25

What is the range of ElastiCache’s TTL?

Answer 25

TTL can range from few seconds to hours or days

Question 26

What ElastiCache pattern is easy to implement and works for many situations as a foundation, especially on the read side?

Answer 26

Lazy Loading / Cache aside

Question 27

With what is usually combined ElastiCache’s Write-through pattern?

Answer 27

with Lazy Loading as targeted for the queries or workloads that benefit from this optimization

Question 28

Setting a TTL is usually not a bad idea, except when…

Answer 28

you’re using Write-through. Set it to a sensible value for your application

Question 29

What is an anti-pattern for ElastiCache?

Answer 29

data changing rapidly, all large key space frequently needed