AWS RDS Overview

• RDS stands for Relational Database Service
• It’s managed DB service for DB use SQL as a query language
• It allows you to create database in the cloud that are managed by AWS
  - Postgress
  - MySQL
  - Oracle
  - MariaDB
  - MSSQL
  - Aurora (AWS proprietary database)

Advantage over using RDS versus deploying DB on EC2

• RDS is a managed service:
  - Automated provisioning, OS patching
  - Continuous backups and restore to specific timestamp
  - Monitoring dashboards
  - Read replicas for improved read performance
  - Multi AZ setup for DR (Disaster Recovery)
  - Maintenance windows for upgrades
  - Scaling capability (vertical and horizontal)
  - Storage backed by EBS
• But you can’t SSH into your instances

RDS Backups

• Backups are automatically enabled in RDS
• Automated backups:
  - Daily full backup of the database
  - Transaction logs are backed-up by RDS every 5 minutes
  - ⇒ ability to restore to any point in time (from oldest backup to 5 minutes ago)
  - 7 days retention (can be increased to 35 days)
• DB Snapshots:
  - Manually triggered by the user
  - Retention of backup fo as long as you want

RD - Storage Auto Scaling

• Helps you increase storage on your RDS DB instance dynamically
• When RDS detects you are running out of free database storage, it scales automatically
• Avoid manually scaling your database storage
• You have to set maximum Storage threshold (maximum limit for DB storage)
• Automatically modify storage if:
  - Free storage is less than %10 of allocated storage
  - Low-storage lasts at least 5 minutes
  - 6 hours have passed since last modification
• Useful for applications with unpredictable workloads
• Supports all RDS database engines (MariaDB, MySQL, PostgreSQL, SQL Server, Oracle)

RDS Read Replicas for read scalability

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

RDS Read Replicas — Use Cases

• You have a production database that is taking on normal load
• Ypu want to run a reporting application to run some analytics
• Ypu create a Read Replica to run the new workload there
• The production application is unaffected
• Read replicas are used for SELECT (=red) only kind of statements (not INSERT, UPDATE, DELETE)

RDS Read Replicas — Network Cost

• In AWS there’s a network cost when data goes from one AZ to another
• For RDS Read Replicas within the same region, you don’t pay that fee

RDS Multi AZ (Disaster Recovery)

• SYNC replication
• One DNS same — automatic app failover to standby
• Increase availability
• Failover in case of loss of AZ, loss of network, instance or storage failure
• No manual intervention in apps
• Not used for scaling

Note: The Read Replicas be setup as Multi AZ for Disaster Recovery (DR)

RDS - From Single-AZ to Multi-AZ

• Zero downtown operation (no need to stop DB)
• Just click on “modify” for the database
• The following happens internally:
  - A snapshot is taken
  - A new DB is restored from the snapshot in a new AZ
  - Synchronization is established between the two databases

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