Calculating Cloud App Availability

Dave Bermingham gives you a way to calculate how available you should expect your application to be given SLAs:

When deploying business critical applications in the cloud you want to make sure they are highly available. The good news is that if you plan properly, you can achieve 99.99% (4-nines) of availability or more. However, calculating your true availability may not be as straightforward as it seems.

When considering availability you must consider the key components that make access to your application possible, which I’ll call the availability chain. Component of the availability chain are:

– Compute
– Network 
– Storage
– Application
– Dependent services

Your application is only as available as your weakest link, and your downtime increases exponentially with each additional link you add to the chain.  Let’s examine each of the links. 

Read on for a breakdown of these items.