But experts say using a second availability zone when you're starting up an AWS instance isn't a panacea to prevent your app from going down during an outage, nor is it as easy to do as simply flipping a switch. And it will cost you more -- sometimes more than double the cost of deploying to a single AZ.

AMAZON TAKES THE BLAME:

MORE CLOUD:

There are a variety of tools for customers to create highly available, fault tolerant systems within Amazon's cloud. One option is to use AWS's own services, specifically its Elastic Load Balancers (ELBs) that allow workloads to be moved from one availability zone into another. However, AWS acknowledged in a about the October outage that even its ELBs were impacted.