Service Level Agreement (SLA)
The SLA defines the uptime percent of a cloud service Azure is agreeing to provide. Should this not be met then Azure is liable for penalties, for example refunds and compensation.
The percentage level translates to the following:
| SLA % | Yearly Downtime Allowed |
|---|---|
| 95% | 18d 6h 17m 27s |
| 99% | 3d 15h 39m 29s |
| 99.9% | 8h 45m 56s |
| 99.99 | 52m 35s |
The SLA of each service should always be checked to ensure it is sufficient for requirements. The SLAs vary between services, deployments and pricing tiers, for example free web services can have a much lower SLA (or no SLA at all) compared to a paid for web service.
To calculate the actual system SLA we multiply the SLAs of the perticipating service, so with the following example:
- App Service - SLA = 99.95%
- Azure SQL - SLA = 99.99%
So:
\[
Actual SLA = App Service SLA * Azure SQL SLA
\]
\[
Actual SLA = 99.95 * 99.99 = 99.94
\]
This equates to 5h 15m 34s of potential annual downtime.