High Availability Database Architecture

Ray Bradford, Principal Product Manager

Overview

General High Availability (HA) Database Principles

HA Database Options on AWS

Amazon Relational Database Service

Architecting for Availability and Durability

Logical Corruption

Compute Node Failure

Storage Failure

Network Disruption

Data Center or Availability Zone Disruption

Database Maintenance (Scaling, Patching)

Technologies for HA - Backups

Logical corruption

Restore operations after storage volume or AZ disruption

Technologies for HA - Replication

Faster than reboot in case of failure

Don’t Forget: Multi-AZ architecture

X Availability

Zone Availability

Zone

Don’t Forget: Backups still have value

Advanced: replication/failover for maintenance

Make changes to replica, failover to it

Practice

Tale of Two Companies

Single-AZ

Nightly Backup Only

Multi-AZ

Backups from Standby

Maintenance on Standby

Online DDL on Replica

Company A Company B

Replication Options

Synchronous vs. Asynchronous

Logical vs. Physical

Asynchronous vs. Synchronous Replication

Asynchronous Replication

Acknowledged as soon as written to the local storage

Lower durability than synchronous

Can fall behind on shipping

Synchronous Replication

Write is not committed until it is written on both replicas

Highest durability

Higher transaction latency

Asynchronous

insert into person values (‘ray’);

Primary Secondary

commit;

Replication Log Relay Log

ray

ACK ACK

DURABLE in ONE LOCATION DURABLE in TWO LOCATION

Synchronous

insert into person values (‘ray’);

Primary Secondary

commit;

Replication Log Relay Log

ray

ACK ACK DURABLE in TWO LOCATION

Logical vs. Physical

Logical

Standard MySQL Replication

Logical statement or transaction is shipped

With MySQL, enables operations on standby (reads, DDL)

Physical

Shipping the physical block changes

• Oracle Dataguard

• Filesystem or block layer replication

• Physical SAN device replication

May not allow operations on standby

Primary

Logical Replication

Buffer

Data

insert into person values(‘ray’);

commit;

Parse

Recovery

Log

Replication

Log

Replica

Buffer

Data

Parse

Recovery

Log

Replication

Log

Relay Log

Single

Threaded

Primary

Physical Replication

Buffer

Data

insert into person values(‘grant’);

commit;

Parse

Recovery

Log

Replication

Log

Replica

Buffer

Data

Parse

Recovery

Log

Replication

Log

Relay Log

Popular Database Engines on EC2

Native, asynchronous

(Semi)-synchronous

Data Guard, RMAN, Oracle Secure Backup Cloud Module

Oracle Database Machine Image (AMI)

Log shipping and DB mirroring

What is Amazon RDS

Managed Relational Database Service

Goals

Make it easy to set up, operate, and scale relational databases in the cloud.

Maintain compatibility with applications and tools.

Supported Engines

MySQL, Oracle

Amazon RDS Features

Pre-configured deployments in minutes with console

DB Instance type scaling (cpu, memory)

Online storage scaling

Amazon CloudWatch integration

Automatic software patching with user control

Backups

Replication

Amazon RDS Backups

Automated Backups

Nightly system snapshots + transaction backup

Enables point-in-time restore to any point in retention period, up to the last 5 minutes

Max retention period = 8 days

DB Snapshots

User-driven snapshots of database

Kept until explicitly deleted

Multi-AZ Deployments for Amazon RDS

Managed fault-tolerance solution for production databases

What is a Multi-AZ deployment?

Amazon RDS creates and maintains a hot standby in a different Availability Zone

In the event of an unplanned or planned outage, Amazon RDS automatically fails over to the standby

MySQL DB Instance

Things to know about Multi-AZ

Replication Type

Synchronous - designed for high data durability

Physical - standby cannot be accessed directly

What events result in automatic failover?

Unplanned (instance failure, storage volume failure)

Planned (instance scaling, patching)

1-2 minute average failover time

Highly Available, Durable, & Scalable MySQL Deployments

Multi-AZ Deployments Read Replicas

THANK YOU