You have an Azure application that uses the services shown in the following table. How should you calculate the composite SLA for the application?

Question

Options

• A0.999 * 0.9999 = 0.9989001 = 99.89001%
• B0.999 / 0.9999 = 0.9991 = 99.91%
• CMax(0.999, 0.9999) = 0.9999 = 99.99%
• DMin(0.999, 0.9999) = 0.999 = 99.9%

• A
  73% (19)
• B
  8% (2)
• C
  15% (4)
• D
  4% (1)

Explanation

Composite SLAs involve multiple services supporting an application, each with differing levels of availability. For example, consider an App Service web app that writes to Azure SQL Database. At the time of this writing, these Azure services have the following SLAs: App Service web apps = 99.95% SQL Database = 99.99% What is the maximum downtime you would expect for this application? If either service fails, the whole application fails. The probability of each service failing is independent, so the composite SLA for this application is 99.95% × 99.99% = 99.94%. That's lower than the individual SLAs, which isn't surprising because an application that relies on multiple services has more potential https://docs.microsoft.com/en-us/azure/architecture/reliability/requirements#understand-service- level-agreements

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