Availability is the percentage of time an application is performing as expected (not to be confound with uptime). - Architecting for reliability on AWS (pluralsight)

To achieve high availability, use

• Redundancy
• Loose coupling (eg: using a queue)

To calculate the availibility of redundant components

• Multiply the failure rate of the components
• Substract that number from 100%

To calculate the availibility of redundant components

• Multiply the failure rate of the components
• Substract that number from 100%