Most of the higher-level services, such as Amazon Simple Storage Service(S3), Amazon SimpleDB, Amazon Simple Queue Service (SQS), and Amazon Elastic Load Balancing (ELB), have been built with fault tolerance and high availability in mind. Service that provide basic infrastructure, such as Amazon Elastic Compute Cloud (EC2) and Amazon Elastic Block Store (EBS), provide specific features, such as availability zones, elastic IP address, and snapshots, that a fault-tolerant and high available system must take advantage of and use correctly. Just moving a system into the cloud doesn't make it fault-tolerant or highly available.
| # | Description |
|---|---|
| 1 | Load Balancing is an effective way to increase the availability of a system. Instances that fail can be replaced seamlessly behind the load balancer while other instances continue to operate. Elastic Load Balancing can be used to balance across instances in multiple availability zones of a region. |
| 2 | Availability zones (AZs) are distinct geographical locations that are engineered to be insulated from failure in other AZs. By placing Amazon EC2 instances in multiple AZs, an application can be protected from failure at a single location. It is important to run independent application stacks in more than one AZ, either in the same region or in another region, so that if one zone fails, the application in the other zone can continue to run. When you design such a system, you will need a good understanding of zone dependencies. |