What is an Azure Availability Zone?
Azure Availability Zones are a great way of providing redundancy for Azure resources.
Each Availability Zone (AZ) essentially contains physically separate Azure datacentres. Every Availability Zone has independent network infrastructure, power and cooling.
The majority of Azure regions provide and support Availability Zones (AZs). Generally speaking, every Azure region will have a minimum of two Availability Zones, and each Availability Zone has a minimum of one datacentre.
Although, most regions have at least three Availability Zones and each Availability Zone has multiple datacentres (DCs), but some regions can be different so I always recommended to check what is available in your chosen region before the solution is designed.
For example, correct at the time of writing, Availability Zones are available in the UK South region but Availability Zones are not available whatsoever in the UK West region.
Typically, Availability Zones are generally labelled Zone 1, Zone 2 and Zone 3.

The above graphic has been created to help visualise the physical architecture and how regions, Availability Zones and Datacentres fit together.
Availability Zone design considerations & examples
Which Availability Zone and how many you actually choose to utilise will depend on the redundancy requirements at the time of design.
To be able to provide some examples let’s assume we have an Azure Virtual Machine (VM) located in the UK South region called VM1.
First example, the business requirement is to ensure VM1 is protected against a zone failure within the UK South region. To ensure this requirement is achieved, the VM would need to be deployed to at least two Availability Zones which would in turn create the multiple VMs required within each zone, this is also known as a zone-redundant resource (a resource available within Availability Zones).
Let’s say VM1 was deployed across two zones, Zone 1 and Zone 2, this means the resource is protected from a complete zone failure. E.g. all datacentres fail within Zone 1 the resource will still be available via Zone 2.
Second example, the business requirement is to ensure VM1 is protected against a single datacentre failure within the UK South region. To ensure this requirement is achieved, at a minimum the VM would need to be deployed to one Availability Zone, this is also known as a zonal resource (a resource available from only one Availability Zone).
However please note, this would not meet the definition of high availability in the same way as using multiple Availability Zones does, as a zonal VM runs only in a single datacentre and would not automatically continue to be available if the datacentre was to fail.
The primary difference with a zonal VM in a single Availability Zone, versus a standalone Virtual Machine in Azure, is there are automatic recovery procedures in place which will attempt to recover or redeploy the VM on a best effort basis within the single Availability Zone.
So let’s say VM1 was deployed to Zone 1 only, if the datacentre hosting the VM failed within Zone 1, Azure will attempt to recover or redeploy the VM within the same Availability Zone on a best effort basis. Naturally, a small window of downtime would exist whilst the VM is being recovered.
However, with a Zonal VM when compared to a zone redundant VM, if the entire zone failed, then the resource would not be available as it is only located in one Availability Zone.
In summary, the differentiator here for a zonal VM versus a zone redundant VM would be the business requirements and need for high availability, as the only way to achieve true “always on” high availability for Azure VMs is to have them deployed across multiple Availability Zones.

Screenshot above is an example from the Azure portal, showing an Azure VMs configuration, which has only been deployed to one Availability Zone.
Please note, resources located in an Availability Zone still benefit from protections against smaller localised issues, i.e. each individual resource located in a specific datacentre is still protected against rack failure.
The Availability Zone service itself is free of charge to utilise which includes bandwidth costs within the same Availability Zone. Please note, if you deploy an Azure VM to multiple Availability Zones, multiple VMs will be created and you will be charged for each VM individually. For example, if you create 1 x standard D4s v3 VM and deploy it to three Availability Zones, three VMs will be created and billed to the subscription.
Network bandwidth between different Availability Zones is also chargeable. Correct at the time of writing, network traffic flowing between different availability zones within the UK South and UK West regions (egress and ingress), is charged at £0.008 per GB. This applies to traffic between any VMs, for example, if you had two VMs in the UK South region but one was in Zone 1 and the other in Zone 3, if these VMs were to communicate with each other the above charges would apply.
Availability Zones (Zone 1, Zone 2 etc) for the same region will also vary between different subscriptions in your tenant, this is due to the logical mapping that occurs during the subscriptions initial creation, this helps Azure to balance capacity across zones whilst maintaining isolation.
I recommend the Azure Pricing Calculator (https://azure.microsoft.com/en-gb/pricing/calculator/) to verify pricing for Azure products and services.
Availability Zone caveats
There are a number of other points which I feel you need to be aware of when it comes to Availability Zones (please note these are correct at the time of writing and are subject to change):
- Trusted launch VMs are not supported within Availability Zones.
- Availability Zones are a method to provide an Azure resource with better redundancy and resiliency within the same region only.
- If a VM is deployed to an Availability Zone it will become what is known as a Zonal VM.
- If a VM is deployed to multiple Availability Zones it will become what is known as a zone redundant VM.
- Azure Public IP addresses and Availability Zones:
- Basic SKU > not compatible with Availability Zones.
- Standard SKU > compatible with Availability Zones and can be used with zonal and zone redundant VMs.
- Standard SKU public IP addresses (PIPs) are available in three types, zone redundant, zonal and non-zonal.
- Zone redundant PIPs are IP addresses which are available to a resource which is located in multiple Availability Zones.
- Zonal PIPs are IP addresses which are available to a resource which is located in a single Availability Zone.
- Non zonal PIPs are IP addresses which are not compatible with Availability Zones and are only to be used with resources that are not located within an Availability Zone.
- As of 2024, Azure standard SKU public IP addresses are zonal by default, meaning they can be used across availability zones.
- Standard SKU public IP addresses (PIPs) are available in three types, zone redundant, zonal and non-zonal.
- It is possible to move a pre-existing VM to an Availability Zone instead of creating a new VM from scratch. However, please note the following:
- This process will copy and transfer the VM over to the selected zone. This requires the VM to be offline causing a small window of downtime.
- The VM will keep the same VM name.
- The process will mean the new zonal/zone-redundant VM will have a new virtual NIC created. The vNIC will be created with the same network settings as the old vNIC and will be connected to the source VNET and Network Security Group (NSG).
- If the VM has a public IP address which is not compatible with an Availability Zone, the process will create another public IP address which is compatible, and will automatically assign it to the respective vNIC.
- You will need to re-configure the new zonal/zone-redundant VM within any applicable Azure Backup, disaster recovery (DR), role based access control (RBAC) and extensions and policies (if required) as it will be seen as a new VM.
- Once the process is fully complete and you have tested to ensure everything is up and running on the new VM, the source VM and move collection (which is created as part of the move process), can be deleted from Azure as they are no longer required.
- Applicable when utilising multiple Availability Zones, Microsoft do not guarantee a set physical distance between facilities, however Microsoft do advise that each facility in and between zones are separated by sufficient distance to limit risk of failure due to localised natural disaster. All whilst maintaining low-latency connectivity between zones typically in single digit millisecond speeds (ms).
Availability Zone summary
Availability Zones should be considered during the initial solution design, ideally not added later as an afterthought, although existing Virtual Machines can be moved to Availability Zones later if required. Availability Zones are extremely useful when high availability and resiliency is required within a single Azure region.
Use Availability Zones when:
- The workload must remain available during a datacentre or zone failure.
- You are designing production or mission‑critical systems located within a single region.
- You can deploy multiple instances of a single resource.
- An increase in cost is acceptable for much higher redundancy.
- You want to meet SLA, compliance, or business continuity requirements.
You may want to avoid Availability Zones when:
- The workload is non‑production (dev, test, lab environments) and you do not require redundancy or cannot justify the uplift in cost.
- You cannot deploy multiple instances of a single resource.
- The chosen Azure region does not support Availability Zones.
- The resource is already protected for disaster recovery purposes across different regions using another solution (look out for my upcoming blog post on Azure Site Recovery) and does not require regional protection.
Hope this helps and thanks for reading!


















