Availability

When you’re deploying an application, a service, or any IT resources, it’s important the resources are available when needed. With high availability, this focuses on ensuring maximum availability, regardless of disruptions or events that may occur.

When architecting a cloud solution, it is important to account for service availability guarantees. Azure SLAs is the formal agreement between the Microsoft Service Provider and Customer for Azure uptime guarantees.

Demystifying Azure SLAs and Uptime Percentages

When it comes to cloud reliability, SLAs and uptime percentages are more than just technical jargon—they're the foundation of trust between cloud providers and businesses. Azure’s SLAs set clear expectations for service availability, helping organizations plan for resilience and continuity.

What is an Azure SLA?

An SLA is a contractual promise from Microsoft that defines the minimum uptime and connectivity you can expect from an Azure service. For example, the SLA for a single Azure Virtual Machine (VM) is 99.9% uptime per month, translating to about 43 minutes of potential downtime monthly.

For services like Azure SQL Database, the guarantees go even higher:

• Standard tiers offer 99.99% uptime;
• Business Critical tier with zone redundancy reaches an impressive 99.995%—less than 30 minutes of downtime per year.

Understanding the "Nines"

Uptime is often discussed in terms of "nines":

• 99.9% ("three nines"): ~43 minutes downtime/month
• 99.99% ("four nines"): ~4 minutes downtime/month
• 99.995%: ~2 minutes downtime/month

Each extra nine significantly reduces potential downtime, which can be crucial for enterprise-critical workloads.

Composit SLAs: The BIG Picture

It's important to remember that when your application relies on multiple Azure services, the overall availability is a combination of each component's SLA. For example, if your app uses both a Web App and a SQL database, the composite SLA will be lower than individual guarantees, since an outage in either affects the whole system.

Takeaway

Azure SLAs provide a transparent benchmark for uptime, empowering enterprises to make informed decisions about cloud adoption and architecture. Whether you're aiming for "three nines" or pushing towards "five nines", understanding these guarantees—and their limitations—is key to building resilient, high-availability solutions in the cloud.