Microsoft Azure is a comprehensive cloud computing platform that provides services for hosting, managing, and scaling applications and infrastructure. Understanding key concepts such as SLAs, resource limits, and regional structures is essential for designing reliable and cost-effective solutions in Azure.
Service Level Agreements (SLA)
An SLA defines the level of availability that Microsoft guarantees for a given service. Common uptime guarantees include:
- 95% uptime → up to 18 days of downtime annually
- 99% uptime → up to 3 days of downtime annually
- 99.9% uptime → up to 8 hours of downtime annually
- 99.99% uptime → up to 1 hour of downtime annually
When multiple services are used together, their effective SLA is the product of each individual SLA. For example, combining App Service (99.95%) and Azure SQL (99.95%) results in an overall SLA of approximately 99.94%.
Availability calculations can be performed using uptime.is.
Azure Resource Limits
Each Azure subscription has default resource quotas, such as:
- 250 storage accounts per region
- 980 resource groups per subscription
- 25,000 virtual machines per region
These limits can be increased by contacting Microsoft support.
Accounts, Subscriptions, and Management Groups
- Accounts: The identity that owns Azure resources.
- Subscriptions: Logical containers that define resource quotas, billing, and access control. Multiple subscriptions can be associated with a single account.
- Management Groups: Hierarchical groupings of subscriptions used to apply governance, policies, and access control consistently across an organization.
Resources, Resource Groups, and Providers
- Resources: Fundamental building blocks such as virtual machines, storage accounts, and databases.
- Resource Groups: Logical collections of resources for simplified management. Resource groups cannot be nested.
- Resource Providers: Services that supply and manage resource types, such as
Microsoft.ComputeandMicrosoft.Storage. - Azure Resource Manager (ARM) Templates: JSON files that declaratively define and deploy resources as Infrastructure as Code.
Availability Zones
Some regions support Availability Zones — physically separate datacenters with independent power, cooling, and networking. They provide higher availability by ensuring workloads remain operational even if one zone becomes unavailable. Zones are interconnected with high-speed private fiber connections. Note that duplicating resources across zones can increase costs.
Paired Regions
Each Azure region is paired with another region within the same geography (at least 300 miles apart). This design provides:
- Failover support in case of a regional outage
- Staggered updates, as Microsoft patches one region before its pair
Sovereign Regions
Sovereign regions are dedicated for government and regulated workloads, operated by screened personnel and offering additional compliance certifications. Examples include:
- US Gov Iowa
- US Gov Virginia
- China East
- China North
Selecting a Region
When deploying a resource, region selection should consider the following:
- Geographic proximity to minimize latency for users
- Service availability, as not all services are offered in every region
- Support for Availability Zones if high availability is a priority
- Pricing differences between regions
Conclusion
A solid understanding of Azure’s SLA, resource limits, organizational structure, and regional design is crucial for building reliable cloud solutions. Considering these factors early in the design process helps ensure availability, compliance, and cost efficiency.