RDS

Question 1

Multi AZ
- cluster vs instance

Answer 1

In cluster, there is one writer and 2 reader nodes all in different AZs (max 2 readers). Application will have to implement logic to load balance usage of the 2 readers.

In instance, there is one primary and failover node. Failover node has to be in same region as primary. Failover is done by changing DNS resolution.

Both have
- Synchronous replication

Question 2

Read replicas in RDS synchronous or asynchronous

Answer 2

Async replication. Can also live in another region.

Question 3

RDS backups

Answer 3

Managed and manual. Stored into s3. Doesn’t auto delete, you need to delete yourself

Question 4

How does RDS restore work from snapshots?

Answer 4

RDS creates a new instance with a new DNS name and takes time because it needs to replay every transaction from backed up transaction logs

Question 5

Using read replica vs snapshots to restore

Answer 5

Read replica
- Can promote RR instantly
- If issue is data corruption, RR won’t help

Snapshots
- Take awhile because it needs to replay events

Question 6

Aurora - difference between Aurora’s read replica to RDS’s read replica and backup node

Answer 6

In RDS, read replicas are not failover nodes by default (though you can manually set it to be). Failover nodes in RDS are just backups and don’t serve traffic. So you must choose between scalability and high availability in RDS.

In Aurora, read replicas are also failover nodes.

Question 7

Aurora vs RDS billing

Answer 7

RDS
- preallocate and pay

Aurora
- high “watermark”. every month, billed the max amount of storage in GB. (will change soon)
- IO cost per request

Question 8

Aurora replicated how many times by default?

Answer 8

6. 3 per AZ and max of 15.

Question 9

Aurora serverless

Answer 9

Same as aurora but charged by ACU which decides compute and storage. Can scale on a MIN and MAX ACU value

Question 10

Aurora multi-master

Answer 10

Single master
- One R/W and replicas
- Failover to replicas take time

Multi master
- All instances are R/W

Question 11

RDS proxy

Answer 11

Long running connection pooler. Use cases
- Lambda. So that connections don’t keep getting created and we can recycle connection
- Long running apps
- “Too many connections” error

Managed service

Question 12

RDS custom

Answer 12

Gives you more control over configurations of your MS SQL and Oracle instances than RDS, but more than deploying on EC2 only