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- Skills Learned
- Describe the purpose of an Azure Service Level Agreement (SLA)
- Identify actions that can impact an SLA (i.e. Availability Zones)
- Study Guide
- Expand your knowledge - extra resources
SLA
Service Level Agreement (SLA) is a formal agreement between a service provider and a customer.
SLA is a promise of a service’s availability (uptime & connectivity). Availability is a measure of time that a service remains operational.
- Each Service has its own SLA
- Ranges from 99% to 99.999%
- Free services typically don’t have an SLA
- Broken SLA means service credit return (discount)
| SLA | Monthly Downtime |
|---|---|
| 99% | 7h 18m 17s |
| 99.5% | 3h 39m 8s |
| 99.9% | 43m 49s |
| 99.95% | 21m 54s |
| 99.99% | 4m 22s |
| 99.999% | 26s |
Formulas
Logical AND - adding dependency
Availability of S1 AND S2 = Availability(S1) * Availability(S2)
Scenario - Azure website with SQL backend db
- Availability = Availability(web) app * Availability(sql)
- Availability = 99.95% * 99.95%
- Availability = 0.9995 * 0.9995
- Availability = 0.99900025
- Availability ~ 99.9%
Logical OR - adding redundancy
Availability of S1 OR S2 = 100% - ( Unvailability(S1) * Unvailability(S2) )
Scenario - Two redundant web apps behind a load balancer
- Availability(both-web) = 100% - ( Unvailability(web1) * Unvailability(web2) )
- Availability(both-web) = 100% - ( 0.05% * 0.05% )
- Availability(both-web) = 1 – ( 0.0005 * 0.0005 )
- Availability(both-web) = 1 – 0.00000025
- Availability(both-web) = 0.99999975
- Availability(both-web) ~ 99.9999%
Key Items
- Formal agreement between Microsoft & the customer
- Calculated as a percentage of service availability (uptime & connetivity) (a promise)
- Breaking the SLA provides a discount from the final monthly bill (Service Credit)
- Higher tier services offer better SLAs
- Free services typically have no SLA (0% SLA)
- Preview services have no SLA
- Composite SLA is a combined SLA of all application components