Overview

This section uses typical web applications as an example to describe the typical architectures deployed with different availability objectives. In each scenario, design an architecture with the items listed in the table below taken into account, so as to achieve the availability objective.

Item	Impact on Application Availability
Redundancy	High availability of application components and automatic service recovery upon faults of some application nodes
Backup	Recovery capability when application data is damaged
DR	Recovery capability in the event of a disaster in a region, AZ, IDC, or other cloud sites
Monitoring metrics and alarms	Capabilities of detection and alarm reporting for application system faults
Auto scaling	Automatic recovery capability when the application capacity is insufficient
Change error prevention	Capability of reducing the downtime caused by changes in applications
Emergency recovery	Emergency recovery capability upon application faults