In this chapter, we will introduce some key design principles and approaches to achieving high availability in your applications deployed on the AWS cloud. As an enterprise or a start-up, you  want to ensure that your mission critical applications are always available to serve your customers. The approaches in this chapter will address availability across the layers of your application architecture including availability aspects of key infrastructural components to ensure that there are no single points of failure.

In order to address availability requirements, we will use AWS infrastructure (Availability Zones and Regions), AWS Foundation Services (EC2 instances, Storage, Security and Access Control, and Networking), and AWS PaaS services (DynamoDB, RDS, CloudFormation, and so on). In addition to availability, we will describe several approaches used for disaster recovery (DR). We will also show you how to implement high availability for our sample application.

In this chapter, you shall learn the following topics:

• Defining availability objectives
• Nature of failures
• Setting up VPC for high availability
• Using ELB and route 53 for high availability
• Setting up high availability for application and data layers
• Implementing high availability in the application
• Using AWS for disaster recovery
• Testing the disaster recovery strategy