SLAs and the Service Lifecycle
😟 THE PROBLEM
A team builds production payments on a preview feature with no uptime promise.
😊 THE SOLUTION
Check SLAs and use generally available services for production.
- Preview features in production✓ Wait for general availability
- Unsure how much downtime to expect✓ Read the SLA percentage
- Several services depend on each other✓ Multiply SLAs, add redundancy
Quick answer
A Service Level Agreement (SLA) is Microsoft's formal commitment to a level of uptime or connectivity for a service, usually as a percentage such as 99.9%, with service credits if it is missed. The service lifecycle describes how services are released: private preview, then public preview (usually no SLA), then general availability (GA), which is fully supported with an SLA.
Start with a question
A brand-new Azure feature is exactly what you need. Should you run your bank’s payments on it today?
Check whether it’s preview or generally available, and what its SLA promises.
Explain it like I’m 10
The technical explanation
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1 Private preview
Invited customers test early versions.
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2 Public preview
Everyone can try it. Usually no SLA, may change.
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3 General availability
Fully supported, typically with an SLA.
- Per week
- Per month
- Per year
Maximum downtime still allowed under the SLA.
Combine two services that both must work
Composite SLA: — lower than either service on its own.
Web app (99.95%) calling a database (99.99%): 0.9995 × 0.9999.
Real-world business scenario
A payments start-up
- The problem
- Engineers wanted to use a preview database feature for the production payment flow.
- What they used
- Kept the preview feature in a test environment and waited for general availability before using it in production.
- Why that choice
- Preview features usually have no SLA and may change.
- The result
- No surprises in production; the feature moved to production after GA.
When to use it and when not to
✓ Use it when…
- Use GA services with SLAs for production.
- Try previews in dev and test.
✕ Think twice when…
- Building critical production paths on preview features.
Interview preparation
Say your answer out loud first, then open the model answer. Interviewers care more about your reasoning than the exact words.
Beginner What is an SLA?
Model answer
A promise from Microsoft about how much of the time a service will be available, like 99.9%. If Microsoft misses it, customers can claim service credits.
Intermediate What is the difference between public preview and general availability?
Model answer
Public preview lets everyone try a new feature, but it usually has no SLA and may change, so it is not recommended for production. General availability means the service is fully released, supported and typically covered by an SLA.
Experienced developer How do you calculate the SLA of an application using several services?
Model answer
Multiply the SLAs of services that all must work, which lowers the overall figure. Add redundancy, such as multiple regions, to increase it. Remember SLAs cover the platform, not your own code or deployments.
Test yourself with exercises
3 original practice questions in the AZ-900 style. Pick your answers, then check them. You will see why each option is right or wrong. Score 75% or more and this topic is marked complete.
Quick revision
Key points
- SLAs are uptime commitments with service credits.
- Composite SLA = multiply SLAs of dependent services.
- Lifecycle is private preview → public preview → general availability.
- Preview services usually have no SLA.
Important terminology
- SLA
- A formal commitment to uptime or connectivity, with service credits if it is not met.
- Service credit
- A percentage of fees refunded when an SLA is missed.
- Public preview
- A service available to all customers for testing, usually without an SLA.
- General availability (GA)
- A fully released, supported service, normally covered by an SLA.
Common mistakes
- Running production on preview features without understanding the risk.
Exam tips
- SLAs and lifecycle are not listed in the current outline, but they underpin high availability and are common interview topics.
Five quick revision questions
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1.What is a service credit?Show
A refund percentage when an SLA is missed.
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2.Do public preview services usually have an SLA?Show
No.
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3.What does GA stand for?Show
General availability.
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4.How do you combine SLAs of services that all must work?Show
Multiply them.
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5.Which has less downtime, 99.9% or 99.99%?Show
99.99%.
Official references
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