Azure VM High Availability SLA Requirements

AZ-900 By islever Editorial Last updated

Describe Azure compute and networking services

Short answer

A Deploying two virtual machines across two availability zones meets the 99.99% Azure VM SLA guarantee.

Question

Note: The question is included in a number of questions that depicts the identical set-up. However, every question has a distinctive result. Establish if
the solution satisfies the requirements.
You are tasked with deploying a critical LOB application, which will be installed on a virtual machine, to Azure.
You are informed that the application deployment strategy should allow for a guaranteed availability of 99.99 percent. You need to make sure that the strategy
requires as little virtual machines and availability zones as possible.
Solution: You include two virtual machines and two availability zones in your strategy.
Does the solution meet the goal?
  1. Yes Correct Answer
  2. No

Key Takeaways

The exam tests knowledge of Azure's official SLA documentation, specifically the trap where candidates might confuse single-zone or availability set deployments (99.95%) with multi-zone deployments (99.99%).

This question tests the specific Azure Virtual Machine Service Level Agreement (SLA) for high availability using Availability Zones. It establishes that deploying two virtual machines across two availability zones is the minimum configuration required to achieve a 99.99% uptime guarantee.

Common mistake: Candidates often select 'No' because they mistakenly believe higher redundancy (more than two VMs/zones) is needed, or they confuse the 99.95% SLA of Availability Sets with the 99.99% SLA of Availability Zones.

Expert Analysis

Why the Answer Is Correct

According to Microsoft's official Azure Virtual Machine SLA, a 99.99% uptime guarantee is provided for all Virtual Machines that have two or more instances deployed across two or more Availability Zones in the same Azure region. The solution proposes exactly this: two virtual machines and two availability zones. This meets the requirement for guaranteed availability while using the minimum number of resources specified (as one VM cannot span multiple zones, and one zone does not provide the zone-redundant SLA).

Why the Other Options Are Wrong

Option B ('No') is incorrect because it implies the strategy fails to meet the goal. However, since the proposed strategy aligns perfectly with the definition of the 99.99% SLA, the answer must be Yes. Any configuration with fewer than two zones or fewer than two instances would typically fall back to lower SLAs like 99.95% (for single zone/availability sets) or 99.0%/99.9% depending on OS.

Community Comment Notes

There was significant confusion in the community due to ambiguous phrasing in some versions of this question. Some users argued for 'No' based on older interpretations or misreading the question as proposing only one VM. However, the consensus among experts and verified comments confirms that 'Yes' is correct when two VMs and two zones are explicitly stated. As noted by user BinuRaj, the SLA documentation explicitly states the 99.99% guarantee applies to VMs with "two or more instances deployed across two or more Availability Zones." User AntonioTech also confirmed this alignment with the official SLA text.

Official Reference

https://www.azure.cn/en-us/support/sla/virtual-machines/

This link opens the official vendor documentation in a new tab.

Exam Strategy

Memorize the specific SLA percentages for Azure services, particularly the distinction between 99.95% (Availability Sets/Single Zone) and 99.99% (Multi-Zone). When questions ask for the 'minimum' resources to hit a specific SLA target, map the target directly to the architectural requirement in the SLA table.

Frequently Asked Questions

Why isn't 99.95% sufficient for this question?

The question explicitly requires a guaranteed availability of 99.99%. The 99.95% SLA applies to Availability Sets or single-zone deployments, which do not meet the stricter requirement.

Can I achieve 99.99% SLA with just one Availability Zone?

No. To receive the 99.99% SLA for Virtual Machines, you must deploy at least two instances across two or more Availability Zones within the same region.

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Discussion 119 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 30 of 119

  1. BinuRaj 👍 99
    SLA for Virtual Machines Last updated: July 2020 For all Virtual Machines that have two or more instances deployed across two or more Availability Zones in the same Azure region, we guarantee you will have Virtual Machine Connectivity to at least one instance at least 99.99% of the time. For all Virtual Machines that have two or more instances deployed in the same Availability Set or in the same Dedicated Host Group, we guarantee you will have Virtual Machine Connectivity to at least one instance at least 99.95% of the time. For any Single Instance Virtual Machine using Premium SSD or Ultra Disk for all Operating System Disks and Data Disks, we guarantee you will have Virtual Machine Connectivity of at least 99.9%. For any Single Instance Virtual Machine using Standard SSD Managed Disks for Operating System Disk and Data Disks, we guarantee you will have Virtual Machine Connectivity of at least 99.5%. For any Single Instance Virtual Machine using Standard HDD Managed Disks for Operating System Disks and Data Disks, we guarantee you will have Virtual Machine Connectivity of at least 95%.
  2. ddponder 👍 29
    The correct answer is B. The correct solution would have a minimum of 2 for both.
  3. Sarmad_Mansour 👍 12
    minimum of 2 for both, then the correct answer should be A.
  4. AntonioTech 👍 11
    The answer is A. Yes The solution meets the goal. Deploying two virtual machines across two availability zones is a suitable strategy for achieving a guaranteed availability of 99.99 percent with the least virtual machines and availability zones. Azure Availability Zones are physically separate datacenters within an Azure region, providing redundancy and high availability. By deploying the application to two virtual machines, each in a different availability zone, you ensure that even if one availability zone experiences an issue, the application remains available in the other availability zone. This setup minimizes the risk of downtime and meets the specified availability requirement of 99.99 percent.
  5. Anonymous learner 👍 10 Answered A
    It's A you noobs
Show 25 more comments
  1. awsORbust 👍 7
    The correct answer is B - NO: The question clearly states that they are looking for 99.99% guaranteed availability and the solution is to include one virtual machine and two availability zones in your strategy. When only One Virtual Machine is used the best availability percentage you can get is 99.95% so the this is not a good solution and the answer is B - NO.
  2. kasho0 👍 7
    A is the correct answer SLA for Virtual Machines Updated: 11/2020 For all Virtual Machines that have two or more instances deployed across two or more Availability Zones in the same Azure region, we guarantee you will have Virtual Machine Connectivity to at least one instance at least 99.99% of the time. https://www.azure.cn/en-us/support/sla/virtual-machines/
  3. pgcool 👍 7
    its mentioned 2 for both. Please dont give wrong answer
  4. Georgess 👍 6
    Actually, with only on VM, the best SLA you get is 99.9% (for any Single Instance Virtual Machine using Premium SSD or Ultra Disk for all Operating System Disks and Data Disks, we guarantee you will have Virtual Machine Connectivity of at least 99.9%). 99.95 is 2+ VM's in the same Availability Set or in the same dedicated host group.
  5. Micha_ 👍 6 Answered B
    What I don’t see anyone pointing out is that with a single VM, you can’t possibly be using multiple AZs, since a VM only exists in one of those by definition.
  6. ITprof99 👍 6
    Recent update to the q? A lot of answers say no but then say the correct solution would have a minimum of 2 for both. Answer: A
  7. Kris_ETL 👍 6 Answered A
    To have 99.99 SLA, you need two virtual machines and two availability zones
  8. tlh45342 👍 5
    Please watch your google search. The solution IN THIS CASE was to deploy 2 VMs. I almost fell into the same trap. The question I was looking at was to deploy 1 VM. If 1 VM deployed this fails. if 2 VMs (as in this question) then A / True.
  9. ryaneven 👍 4
    An Availability Zone in an Azure region is a combination of a fault domain and an update domain. For example, if you create three or more VMs across three zones in an Azure region, your VMs are effectively distributed across three fault domains and three update domains. The Azure platform recognizes this distribution across update domains to make sure that VMs in different zones are not scheduled to be updated at the same time.
  10. NewInAZ 👍 4 Answered A
    Answer is A, because of: "For all Virtual Machines that have two or more instances deployed across two or more Availability Zones in the same Azure region, we guarantee you will have Virtual Machine Connectivity to at least one instance at least 99.99% of the time."
  11. jrmunoza 👍 4
    One VM with Two instances and two or more availability Zones we gan get 99.99 % availability.
  12. Jeenia 👍 4 Answered A
    Having 2 VMs at two different locations/availability zones solves the problem.
  13. Mandal6002 👍 4 Answered A
    Two or more virtual machine with two or more availability zone
  14. KostaStern 👍 4
    You get 99.9% with premium SSD But the question was 99.99%
  15. jerborder 👍 4 Answered A
    >=2 VMs and >= 2 ARs = 99.99% availability.
  16. nsp24 👍 4 Answered A
    Answer has been updated its correct now.
  17. kate_py 👍 4
    We will need at least two VMs.
  18. Foow 👍 4
    Sorry I mean A.
  19. fg2022 👍 4 Answered A
    A is correct
  20. Souban07 👍 3
    A. Yes, the solution meets the goal of guaranteed availability of 99.99 percent. By including two virtual machines and two availability zones in your deployment strategy, you are providing a level of redundancy and resiliency that can help ensure the availability of your critical LOB application. With two virtual machines, you can set up load balancing to distribute incoming traffic across both instances, reducing the risk of a single point of failure. By deploying the virtual machines in two separate availability zones, you are providing an additional layer of protection against outages or failures in a single location. However, it's important to note that availability targets are best-effort and not guaranteed. To further ensure the availability of your application, you should also implement disaster recovery strategies and backup solutions, such as Azure Backup or Azure Site Recovery, to ensure the recoverability of your application in the event of a failure.
  21. P_BASNET 👍 3
    A. Yes Deploying two virtual machines across two availability zones can meet the goal of achieving 99.99% availability. Here’s why: Availability Zones: Using two availability zones provides high availability by ensuring that if one zone experiences a failure, the other zone can continue to operate, thereby reducing the risk of total service disruption. Virtual Machines: With two virtual machines spread across these availability zones, you achieve redundancy and fault tolerance. If one virtual machine fails, the other can handle the workload, ensuring continuous operation. This setup meets the requirements for high availability with minimal resource use, aligning with the goal of 99.99% availability. So, the correct answer is A. Yes.
  22. Luansi 👍 3 Answered A
    https://azure.microsoft.com/en-us/support/legal/sla/virtual-machines/v1_9/ For all Virtual Machines that have two or more instances deployed across two or more Availability Zones in the same Azure region, we guarantee you will have Virtual Machine Connectivity to at least one instance at least 99.99% of the time.
  23. Fyrus 👍 3 Answered A
    "For all Virtual Machines that have two or more instances deployed across two or more Availability Zones in the same Azure region, we guarantee you will have Virtual Machine Connectivity to at least one instance at least 99.99% of the time." https://www.azure.cn/en-us/support/sla/virtual-machines/
  24. NewInAZ 👍 3
    Answer is "YES". Please, kindly read: "For all Virtual Machines that have two or more instances deployed across two or more Availability Zones in the same Azure region, we guarantee you will have Virtual Machine Connectivity to at least one instance at least 99.99% of the time."
  25. ClaGar 👍 3
    Solution statement ''You include two virtual machines and two availability zones in your strategy'' might lead to confusion because it might mean ONE VM in each of the two Availability Zone.

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