11 - RDS Multi-AZ and Read Replicas

Question 1

Multi-AZ RDS

Answer 1

Multi-AZ RDS

• Multi-AZ RDS is for disaster recovery only.
• It is not used for improving performance.
• To improve performance you need read-replicas

Question 2

Read Replicas

Answer 2

Read Replicas

• Used for scaling, not disaster recovery
• Must have automatic backups turned on in order to deploy a read replica
• You can have up to 5 read replica copies of any database
• You can read replicas of read replicas (but long latency)
• Each read replica will have its own DNS end point
• You can have read replicas that have multi-AZ enabled
• You can crate read replicas of multi-AZ source databases
• Read replicas can be promoted to their own databases (this breaks the read replication)
• You can have a read replication in another region (for MySQL and MariaDB)

Question 3

DB Backups - Overview

2 types - Automated Backups & Database Snapshots

Answer 3

DB Backups - 2 types - Automated Backups & Database Snapshots

Automated Backups

• Can recover database to any point in time, within a “retention period”.
• The period can be between 1 - 35 days.
• This is a full daily snapshot, and will also store transaction logs through out the day.
• When recover will first pull the most recent daily backup, and then apply all relevant transaction logs to that day.
• This allows for point in time recovery down to a second, with a retention period.
• They are enabled by default.
• Backup data stored in S3, and you get free storage equal to the size of your database.
• Backups are taken within a defined window
• During back up window, storage I/O may be suspended while data is being backed up which could cause elevated latency

Database Snapshots

• Snapshots are done manually (user initiated)
• Snapshots are stored even after you delete the original RDS instance (unlike automated backups which are deleted if the database is deleted)