Exam AZ-104 topic 4 question 14 discussion

Correct Answer: A VM Scale Set consists of a set of identically configured VMs. Availability Set consists of a set of discrete VMs. No more than 20% of the Scale Set upgrading at any time, then 2 machines out of 10 will have maintenance, the 8 remaining VMs will be up. Virtual machine scale sets are created with five fault domains by default in Azure regions with no zones. For the regions that support zonal deployment of virtual machine scale sets and this option is selected, the default value of the fault domain count is 1 for each of the zones. FD=1 in this case implies that the VM instances belonging to the scale set will be spread across many racks on a best effort basis. Reference: https://docs.microsoft.com/en-us/azure/virtual-machines/manage-availability https://docs.microsoft.com/en-us/learn/modules/build-app-with-scale-sets/2-features-benefits-virtual-machine-scale-sets https://docs.microsoft.com/en-us/azure/virtual-machine-scale-sets/virtual-machine-scale-sets-automatic-upgrade

Answer is wrong. The correct Answer is A. First: in case you created on fault domain, you are limited with one update domain. You can test this. Second: By default, Azure uses 5 update domains and up to 3 fault domains. So, In case you created 10 vm in scale set. then you will have 2 vm in each update domain. So once one update domain is not available, then you get 4 domains with 8 vms as required.

Answer C Option A might work, but only if the VM scale set has enough update domains configured (not stated). Option C explicitly guarantees the necessary isolation for updates because the number of update domains is stated. Therefore, C is the safest, most correct answer given the information.

Option Explanation Why it's right or wrong A. One virtual machine scale set with 10 VM instances Correct. A scale set with 10 instances ensures Azure can rotate maintenance across instances, keeping at least 8 VMs running. Right choice B. One availability set with 3 fault domains and 1 update domain This will distribute VMs across hardware and maintenance domains, but it doesn’t automatically ensure scalability or manage exact numbers like a scale set does. Availability sets are better for smaller fixed deployments. Not scalable or flexible C. One availability set with 10 update domains and 1 fault domain More domains improve distribution during maintenance but still doesn’t handle dynamic scaling. You’d have to manually ensure 8 VMs stay online. Not dynamic D. One virtual machine scale set with 12 VM instances This would work, but it’s over-provisioning. You would run more VMs than needed, which increases costs unnecessarily. Waste of resources

Correct Answer: A

o1 : correct C Why Not A or D (Scale Sets)? A virtual machine scale set can automatically scale up or down, but it does not inherently guarantee a minimum running count during an update without configuring update policies.

https://learn.microsoft.com/en-us/azure/virtual-machine-scale-sets/virtual-machine-scale-sets-automatic-upgrade "Before you begin the upgrade process, the orchestrator will ensure that no more than 20% of instances in the entire scale set are unhealthy (for any reason). The upgrade orchestrator identifies the batch of VM instances to upgrade, with any one batch having a maximum of 20% of the total instance count, subject to a minimum batch size of one virtual machine. There is no minimum scale set size requirement and scale sets with 5 or fewer instances will have 1 VM per upgrade batch (minimum batch size)." So the answer is A

Straight away I thought C as this as availability sets is designed for this specific scenario

it´s A

on the exam today 6/6/2024

10 update domains... from 5, we start puting 2 together UD1 - VM1 UD2 - VM2 UD3 - VM3 UD4 - VM4 UD5 - VM5 from here... we start puting the next VMS in the already assigned UD 1 by 1 VM6 -> UD1 VM7 -> UD2 VM8 -> UD3 VM9 -> UD4 VM10 -> UD5 Only 1 Update Domain is updated at time... We will always have 4 update Domain On... which guarantees 8 VMs On always

Correct Answer: C Option A suggests using a virtual machine scale set (VMSS) consisting of 10 virtual machine instances. However, the requirement states that the application must run on at least eight virtual machines during planned Azure maintenance. The virtual machine scale set (VMSS) can automatically scale the number of virtual machine instances based on workload or defined scaling rules. However, it does not guarantee that there will be at least eight virtual machine instances running during planned maintenance. In contrast, option C proposes using an Availability Set with 10 update domains and one fault domain. This ensures that during planned maintenance, at least eight virtual machine instances will be available to run the application, meeting the specified requirement.

Answer is A. A-> UD is fixed at 5 for scale set. so during maintenance, 2 Vms will be down at each time. giving us at least 8VMs runing B-> Does not meet the min 8 virtual machines requirement c->Not possible. availability Set will spread out the VM into 2-3 FD depends on region. so min is 2 FD for high availability. ( Look at the comparision between scale sets and availability set under high availability in https://learn.microsoft.com/en-us/azure/virtual-machine-scale-sets/virtual-machine-scale-sets-orchestration-modes) D->will have min 9 or 10VM running

A is correct

The minimum number of fault domains required for an availability set containing 10 virtual machines is 31. Each fault domain represents a group of VMs that are placed in separate physical racks or clusters to minimize correlated failures. By distributing the VMs across fault domains, you enhance reliability and reduce the risk of simultaneous failures affecting related VMs. Additionally, an availability set can be configured with up to 20 update domains2. Update domains determine groups of VMs that can be rebooted together during planned maintenance. However, the order of update domains being rebooted may not proceed sequentially.

A is correct

This was on my exam. The correct answer is provided by the one and only mlantonis.