Azure Availability Zones and Sets

When migrating mission-critical applications to Azure, it is essential to make them resilient to various failures, including data center and rack failures. Azure provides features like Availability Zones and Availability Sets to achieve high availability.

1. Azure Availability Zones

Definition

• Availability Zones are high availability offerings designed to protect applications and data from data center failures. Each Azure region consists of multiple, physically separate data centers.

Key Features

• Isolation: Each Availability Zone is independent, with its own power, cooling, and physical security.
• Data Redundancy: By deploying resources across multiple Availability Zones, applications can remain available even if one zone experiences an outage.

Usage

• When deploying services in Azure, you can select specific Availability Zones to ensure your applications are distributed across them.

2. Azure Availability Sets

Definition

• Availability Sets provide redundancy within a single data center and are a logical grouping of virtual machines (VMs). They help Azure understand how the application is structured to provide redundancy and high availability.

Key Components

• Fault Domain:
  • A fault domain represents a group of underlying hardware that shares a common power source and network switch. It is similar to a rack in an on-premises data center.
  • Deploying VMs within different fault domains ensures that a hardware failure in one domain does not affect VMs in other domains.
• Update Domain:
  • An update domain is a logical group of hardware that can undergo maintenance or reboot at the same time.
  • Azure manages updates and maintenance, ensuring that not all VMs in an Availability Set are affected simultaneously.

Managed Disk Fault Domains

• For VMs using Azure Managed Disks, VMs are aligned with managed disk fault domains when using a managed availability set. This alignment guarantees that all managed disks attached to a VM are in the same fault domain, enhancing the application’s resilience.

3. Traffic Management and Load Balancing

In addition to Availability Zones and Sets, Azure provides services that help in managing traffic and ensuring high availability:

Azure Traffic Manager

• Traffic Manager can monitor endpoints located in different regions. If an endpoint becomes unreachable, it can route traffic to other regional endpoints.
• Routing Methods:
  • Priority: Routes traffic based on priority assigned to each endpoint.
  • Weight: Distributes traffic according to weights assigned to each endpoint.
  • Performance: Routes traffic to the endpoint with the lowest latency.
  • Geographic: Routes traffic based on the geographic location of the user.

Azure Load Balancer

• Azure Load Balancer distributes incoming traffic among VMs or services. It operates at layer-4, using attributes like source IP, source port, destination IP, destination port, and protocol.
• It is ideal for balancing traffic between multiple web servers or application servers.

Application Gateway

• Application Gateway is designed for load balancing traffic based on URL-based routing. It allows hosting multiple sites on the same public IP address.
• This is particularly useful for scenarios where applications require intelligent routing based on the content of the requests.

By utilizing Azure’s Availability Zones, Availability Sets, Traffic Manager, Load Balancer, and Application Gateway, organizations can create resilient and highly available applications capable of withstanding various types of failures.