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
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Adam Marczak

Programmer, architect, trainer, blogger, evangelist are just a few of my titles. What I really am, is a passionate technology enthusiast. I take great pleasure in learning new technologies and finding ways in which this can aid people every day. My latest passion is running an Azure 4 Everyone YouTube channel, where I show that Azure really is for everyone!

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