4.1.3. Design for High Availability

💡 First Principle: High availability is achieved by systematically eliminating single points of failure through redundancy across independent fault domains, ensuring continuous operation despite component or datacenter failures.

Scenario: You are designing a new mission-critical application. It needs to remain operational even if a single server fails, or if an entire datacenter within an Azure Region experiences an outage.

High Availability (HA) ensures a system remains operational and accessible, minimizing downtime by deploying redundant components across isolated infrastructure and enabling automatic failover mechanisms.

This task delves into the practical application of HA services. You'll explore how to:

• Design for Azure Availability Zones: Isolate workloads and provide fault tolerance against datacenter-level failures.
• Design for Azure Availability Sets: Distribute VMs across isolated hardware clusters within a single datacenter.

Mastering these concepts is crucial for the AZ-305 exam, as it assesses your ability to analyze, evaluate, and create resilient HA designs.

⚠️ Common Pitfall: Deploying all tiers of an application into a single Availability Zone. While simpler, this creates a single point of failure at the datacenter level.

Key Trade-Offs:

• Availability Zones vs. Availability Sets: Availability Zones provide a higher level of availability (protection from datacenter failure) but are not available in all regions and may have slightly higher inter-zone latency. Availability Sets protect against hardware failure within a datacenter.

Reflection Question: How do Azure's HA options (Availability Zones and Availability Sets) collectively ensure high availability and fault tolerance for your applications by providing distinct levels of redundancy against various failure scenarios?