8. RDS + Aurora + ElastiCache

Question 1

What are the steps to encrypt an unencrypted RDS database?

Answer 1

1. Create a snapshot of the unencrypted database
2. Copy the snapshot and enable encryption for the snapshot
3. Restore the database from the encrypted snapshot
4. Migrate applications to the new database, and delete the old database

Question 2

What databases are supported by ElastiCache?

Answer 2

Redis and Memcached

Question 3

What features come with Redis?

Answer 3

• Multi-AZ with Auto-Failover
• Read replicas to scale reads and have high availability
• Data Durability using AOF persistence
• Backup and restore features

Question 4

What features come with Memcached?

Answer 4

• Multi-node for partitioning of data (sharding)
• No high availability (replication)
• Non-persistent
• No backup and restore
• Multi-threaded architecture

Question 5

What databases does RDS support?

Answer 5

1. Postgres
2. MySQL
3. MariaDB
4. Oracle
5. Microsoft SQL Server
6. Aurora (AWS proprietary database)

Question 6

You have set up read replicas on your RDS database, but users are complaining that upon updating their social media posts, they do not see their updated posts right away. What is a possible cause for this?

Answer 6

Read replicas have asynchronous replication, therefore it’s likely your users will only read eventual consistency

Question 7

You are running an ElastiCache Redis cluster which you want to ensure is high availability. What should you do?

Answer 7

Enable multi-AZ

Question 8

Which databases does Amazon Aurora support?

Answer 8

MySQL and PostgreSQL

Question 9

How many Aurora Read Replicas can you have in a single Aurora DB Cluster?

Answer 9

15

Question 10

How many Read Replicas can you have in a single RDS database?

Answer 10

15

Question 11

How does the cost of Aurora compare to RDS?

Answer 11

Aurora costs more than RDS (20% more) but is more efficient

Question 12

What is the Aurora Backtrack feature?

Answer 12

Backtrack allows you to restore data at any point in time without using backups

Question 13

What are the 3 ways in which cache evictions can occur?

Answer 13

1. You delete the item explicitly in the cache
2. Item is evicted bc the memory is full and it’s not recently used
3. You set an item time-to-live (TTL)

Question 14

If too many eviction happen due to memory, what you should you do?

Answer 14

Scale up or out

Question 15

What are the pros and cons of a Lazy Loading cache invalidation strategy?

Answer 15

Pros:
- Only requested data is cached; cache isn’t filled with unused data

Cons:
- Cache miss penalty results in 3 round trips
- Stale data - data can be updated in db and outdated in cache

Question 16

What are the pros and cons of a Write Through cache invalidation strategy?

Answer 16

Pros:
- reads are quick; data in cache is never stale

Cons:
- Cache churn; a lot of data will never be read