Section9: AWS Fundamentals:RDS + Aurora + ElastiCache

Question 1

What RDS database do you get in AWS?

Answer 1

• Postgres
• MySQL
• MariaDB
• Oracle
• Microsoft SQL Server
• Aurora

Question 2

Mention a few things regarding RDS Read Replicas for read scalabilities

Answer 2

• Up to 5 read replicas
• Within ZA,Cross AZ or Cross Region
• Replication is ASYNC, so reads are eventually consistent.
• Replicas can be promoted to their own DB.
• Applications must update the connection string to leverage read replicas.

Question 3

What happens when you change your RDS from a Single-AZ to Multi-AZ?

Answer 3

• Note: Zero downtime operation
• The following will happen internally:
  -> A snapshot is taken
  -> A new DB is restored from the snapshot in a new AZ
  -> Synchronization is established between the two databases.

Question 4

Describe Amazon Aurora

Answer 4

• Aurora is a proprietary technology from AWS(not open source)
• Postgres and MySQL are both supported as Aurora DB
• Aurora is “AWS cloud optimized” and claims 5x performance improvement over MySQL and Postgres.
• Aurora storage automatically grows in increments of 10Gig, up to 128 TB.
• Aurora can have 15 replicas while MySQL has 5
• Failover in Aurora is instantaneous.
• Aurora cost more than RDS(20% more).

Question 5

Aurora High Availability and Read Scaling

Answer 5

1) 6 copies of your data across 3 AZ:
- 4 copies out of 6 needed for writes
- 3 copies out of 6 need for read
- Self healing
- Storage is striped across 100s volumes
2) One Aurora Instance takes writes(master)
3) Automated failover for master in less than 30 seconds
4) Support for Cross Region Replication

Question 5

ElastiCache - Redis vs Memcached

Answer 5

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

Memcached:
- Multi-node for portioning of data
- No high availability
- Non persistent
- No backup and restore
- Multi-thread architecture

Question 5

ElastiCache - Cache Security

Answer 5

1) All caches in ElastiCache:
- Do not support IAM authentication
- IAM policies on ElastiCache are only used for AWS API-level security
2) Redis AUTH
- You can set a “Password/token” when you create a Redis cluster
-Support SSL in flight encryption
3) Memcached
- Supports SASL-based authentication

Question 5

3 Patterns for ElastiCache

Answer 5

1) Lazy loading: all the read data is cached, data can become stale in cache.

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

3) Session Store: Store temporary session data in a cache(using TTL features)

Question 5

ElastiCache - Redis Use Case

Answer 5

• Gaming Leaderboards are computationally complex
• Redis Sorted sets guarantee both uniqueness and element ordering
• Each time a new element added, its ranked in real time, then added in correct order.

Question 6

Importane Ports to remember

Answer 6

• FTP:21
• SSH:22
• SFTP:22
• HTTP80
• HTTPS:443
• PostgreSQL:5432
• MySQL:3306