Relational Database Service (RDS)

Icon

Introduction

RDS dont allow access to underlying EC2 instances. So one cannot SSH into the machine running the RDS, except when using RDS custom service.

Features

Storage Auto Scaling

This feature helps in increasing the storage on your DB instance dynamically.
When this feature is enabled RDS detects when the database is running out of space (based on threshold value: Maximum Storage Threshold), will automatically scale the storage.
No manual intervention is needed for scaling when this feature is enabled.
Maximum Storage Threshold parameter can be configured based on,
- Percentage of space left.
- Low storage last for a specific duration.
- Time passed since last modification.
Useful for applications with unpredictable workload.
This feature is available for all RDS database engines.

Read Replicas

When an application is burdened by read and write operation on single node of database then, it is possible that single node may go down becoming single point of failure.
To avoid this, a common strategy is to horizontally scale the database instance to handle reads and writes to separate instances.
RDS allows upto 15 Read Replicas to scale the read operation.
These Read Replicas can be on same AZ, cross AZ or cross-region.
Replication done is ASYNC, so reads are eventually consistent.
Replicas can be promoted to their own database when needed, which may allow them to take writes.
If RDS Read Replication is within same region is free i.e different AZ, cross-region is chargeable.
More can be read here.

Multi AZ

This feature is used for disaster recovery and not for scaling.
With this feature, one get a standby instance.
One DNS name is associated with both master and stand by instance.
This increases availability of the service and provides failover in case of loss of AZ in which master instance resides.
Read Replicas can be setup as Multi AZ for Disaster Recovery (DR).
The replication between standby and master instance is synchronous.
Conversion of Single-AZ database instance to Multi-AZ can be done with zero downtime. Internally, it is basically
- Taking a snapshot of the DB and restore it in new AZ.
- Establish synchronization between two instances.

Previous05_RDS NextAurora

Last updated 2 months ago

Introduction

RDS dont allow access to underlying EC2 instances. So one cannot SSH into the machine running the RDS, except when using RDS custom service.

Features

Storage Auto Scaling

This feature helps in increasing the storage on your DB instance dynamically.

When this feature is enabled RDS detects when the database is running out of space (based on threshold value: Maximum Storage Threshold), will automatically scale the storage.

No manual intervention is needed for scaling when this feature is enabled.

Maximum Storage Threshold parameter can be configured based on,

Percentage of space left.
Low storage last for a specific duration.
Time passed since last modification.

Useful for applications with unpredictable workload.

This feature is available for all RDS database engines.

Read Replicas

When an application is burdened by read and write operation on single node of database then, it is possible that single node may go down becoming single point of failure.

To avoid this, a common strategy is to horizontally scale the database instance to handle reads and writes to separate instances.

RDS allows upto 15 Read Replicas to scale the read operation.

These Read Replicas can be on same AZ, cross AZ or cross-region.

Replication done is ASYNC, so reads are eventually consistent.

Replicas can be promoted to their own database when needed, which may allow them to take writes.

If RDS Read Replication is within same region is free i.e different AZ, cross-region is chargeable.