Describe availability zones

Understanding Availability Zones

In the simplest terms, availability zones comprise physically separated data centres within a region, each with independent power, cooling, and networking. They are parts of Azure’s redundancy and high availability offerings, which protect applications and data from potential failures.

Each Azure region is made up of at least three distinct zones to ensure fault tolerance if a disaster strikes. In other words, they are designed to prevent the complete failure of a specific application hosted in one geographical area.

How Availability Zones Work

To ensure applications are highly available, Azure spreads copies of data and replicates applications across zones in the same region. A zone might be a single building or comprised of multiple buildings. Services, VMs, and data in one availability zone are isolated from services in other zones to enhance security, fault tolerance, and performance.

To take a specific example, if you deploy an Azure Kubernetes Service (AKS) cluster across multiple Availability Zones, that way, each node of the cluster resides in a different zone; even in case of a zone failure, the AKS cluster will continue to function and serve requests.

Availability Zones vs. Region Pairs

It’s essential to understand the distinction between Availability Zones and Region Pairs for better implementing and architecting Azure landscapes. A Region Pair consists of two regions in the same geography, paired together for disaster recovery purposes. Data replicated in a region pair stays within the same geography for compliance and ensure higher durability than Availability Zones. In contrast, Availability zones offer high availability within the same region by protecting against zone failures.

Advantages of Using Availability Zones

Azure’s Availability Zones offer multiple advantages:

• High Availability: The key advantage of using availability zones is high availability. They offer a Service Level Agreement (SLA) of 99.99% for virtual machines, making them an excellent option for running mission-critical applications.
• Fault Isolation: Each availability zone operates independently, thus mitigating localized outages’ impacts. If one zone goes down, the other zones will continue to operate, minimizing downtime and data loss.
• Flexibility: You can architect your applications to replicate data and services across zones to ensure business continuity.

Implementing Availability Zones

Within Azure portal, during the creation of a service or a resource, given the service supports it, you can elect which Availability Zone your service should reside. For instance, while creating a virtual machine, one can select an availability zone under the ‘Settings> Availability options’ section.

You can also configure zone-redundant services, where Azure replicates automatically the applications and data across availability zones, exceptionally beneficial for applications needing high availability.

In conclusion, Azure Availability Zones are an essential feature that allows for high availability, disaster recovery, and fault isolation. While studying for the AZ-900 exam, one should understand the concept, its purpose, how to implement it, and its advantages. While architecting solutions on Azure, the judicious use of Availability Zones can help construct a remarkably resilient infrastructure.

Practice Test

True or False: Availability Zones in Azure are the unique physical locations within a region.

Answer: True.

Explanation: Each Azure region consists of several datacenters spread out over a geographic area, also known as Availability Zones.

How many Availability Zones does Azure provide in each supported region?

• A. 1
• B. 3
• C. 5
• D. 7

Answer: B. 3

Explanation: Azure guarantees the availability of at least three separate zones in all enabled regions to ensure resiliency.

True or False: All Azure regions have Availability Zones.

Answer: False.

Explanation: While Azure always aims to provide Availability Zones in all regions, not all geographic regions currently have Availability Zones.

Availability Zones in Azure are basically:

• A. Different Regions
• B. Separate Datacenters
• C. Resource Groups
• D. Virtual Networks

Answer: B. Separate Datacenters

Explanation: Availability Zones in Azure refer to unique physical locations within a region, essentially different data centers.

True or False: Azure services that support Availability Zones fall into two categories; Zonal services and Zone-redundant services.

Answer: True.

Explanation: Some Azure services can be pinned to specific zones (Zonal services), whereas others can be replicated across zones (Zone-redundant services) for higher availability and resilience.

Which of the following is NOT a benefit of Azure Availability Zones?

• A. Increased availability
• B. High durability
• C. Lower costs
• D. Disaster recovery

Answer: C. Lower costs

Explanation: While Availability Zones provide higher availability, durability and support for disaster recovery, utilization of these zones may result in additional costs.

The failure of one Availability Zone means the whole Azure region will go down.

• A. True
• B. False

Answer: B. False

Explanation: Each Availability Zone is isolated and failure of one does not impact the other Zones within the same region.

Azure Availability Zones are interconnected with ____

• A. Firewalls
• B. Azure Private Links
• C. High-speed private links
• D. VPN Gateways

Answer: C. High-speed private links

Explanation: The Availability Zones within an Azure region are interconnected through high-speed, private links to provide low-latency network connection.

True or False: Within an Azure region, you cannot deploy an application spread across multiple Availability Zones.

Answer: False.

Explanation: It’s recommended to deploy applications across multiple Availability Zones within a region for high availability and fault tolerance.

Azure Availability Zones do not provide protection from ____

• A. Network failures
• B. Power failures
• C. Cooling failures
• D. Regional outages

Answer: D. Regional outages

Explanation: While Azure Availability Zones protect against failures within a single Zone (like hardware, power, cooling, or network failures), they do not protect against larger-scale, regional outages. For that level of protection Azure recommends using a multi-region architecture.

Interview Questions

What are Availability Zones in Microsoft Azure?

Availability Zones are unique physical locations within an Azure region. Each zone is made up of one or more data centres equipped with independent power, cooling, and networking.

What is the primary purpose of Availability Zones?

The primary purpose of Availability Zones is to protect applications and data from datacentre failures or complete zone level disasters by ensuring high availability and disaster recovery.

How many minimum availability zones are present in all enabled regions?

All enabled regions have a minimum of three separate zones to ensure resiliency.

How are Availability Zones identified?

Availability Zones are identified by numbers (1,2,3) within each Azure region.

What Azure service can we use to distribute traffic to the virtual machines in different availability zones?

Azure Load Balancer or Azure Traffic Manager service can be used to distribute network traffic to virtual machines in different availability zones.

Do Availability Zones provide isolation at the network layer?

Yes, Availability Zones are separate, physical locations and provide isolation at the physical, infrastructure, and network layer.

Can users choose the Availability Zones for their resources in Azure?

Yes, users can choose in which Availability Zone their resources are placed.

Can an Azure Virtual Machine (VM) span multiple Availability Zones?

No, an individual Azure Virtual Machine (VM) cannot span multiple Availability Zones. However, a VM scale set can span multiple zones.

Are Availability Zones related to Azure regions?

Yes, Availability Zones are part of Azure’s global infrastructure, and they reside within Azure regions.

How does Azure charges for outbound data transfer between Availability Zones?

Azure does charge for outbound data transfer between Availability Zones within the same region.

What distinguishes Availability Zones from update domains and fault domains in Azure?

Availability Zones are unique physical locations within a region. Each zone is made up of one or more data centers with independent power, cooling, and networking. Fault domains define the group of VMs that share a common power source and network switch. While update domains are logically grouped to coordinate updates.

Is there any latency between Availability Zones within the same region?

No, there is no noticeable latency. Azure guarantees a round-trip latency of less than 2 milliseconds between Availability Zones within the same region.

Can one Azure region have more than three Availability Zones?

Yes, although all enabled regions guarantees a minimum of three separate zones, some regions may have more than three Availability Zones.

Does using multiple Availability Zones increase overall cost?

Yes, deploying instances in multiple Availability Zones increases the overall cost.

When would you use an Availability Set instead of Availability Zones in Azure?

You might use Availability Sets instead of Availability Zones when your application isn’t distributed in nature or when cost is a main concern as deploying VMs across zones can be more expensive due to inter-zone data transfer costs. Availability Sets are a good choice when you want to eliminate single points of failure within a data center, but don’t need to protect against a complete data center failure.