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Difficulty: HardConfigure Azure Load Balancer

An administrator deploys two virtual machines named VM-West1 and VM-West2 to the same virtual network. VM-West1 is deployed in Availability Zone 1, and VM-West2 is deployed in Availability Zone 2.

The administrator deploys a public load balancer named LB-App and successfully configures a frontend IP address using a public IP address named IP-App1.

When attempting to configure the backend pool for LB-App, the administrator discovers that both VM-West1 and VM-West2 cannot be added to the same backend pool.

What is the cause of this issue?

  1. LB-App is configured as a Basic SKU load balancer.Answer
  2. B
    IP-App1 is configured as a Standard SKU public IP address.
  3. C
    VM-West1 and VM-West2 are not associated with a Network Security Group (NSG).
  4. D
    LB-App is configured to use a dynamic private IP address allocation for its backend pool.

Answer

LB-App is configured as a Basic SKU load balancer.
The correct answer is that the load balancer is configured as a Basic SKU. A Basic SKU load balancer does not support backend pools containing virtual machines distributed across different Availability Zones. To load balance across virtual machines in different Availability Zones, a Standard SKU load balancer must be deployed.

Step-by-Step Solution

1
Analyze the network configuration of the backend virtual machines.
VM-West1 is in Availability Zone 1 and VM-West2 is in Availability Zone 2, meaning they are distributed across different Availability Zones.
This establishes the zonal layout of the resources, which has specific SKU compatibility requirements in Azure.
2
Evaluate the backend pool constraints of Azure Load Balancer SKUs.
Basic SKU load balancers only support backend pools consisting of virtual machines in a single Availability Set or Virtual Machine Scale Set. Standard SKU load balancers support any virtual machines within a single virtual network, including those in different Availability Zones.
This identifies the SKU-specific capability mismatch regarding Availability Zones.
3
Determine the cause of the configuration failure based on the successful frontend setup.
Since IP-App1 was successfully associated with LB-App's frontend, the IP SKU and Load Balancer SKU must match (either both Basic or both Standard). Because zonal VMs cannot be added to the backend pool, the load balancer SKU must be Basic.
Connecting the failure to add zonal VMs to the backend pool confirms that the load balancer is configured with the Basic SKU, which does not support zonal backends.

Key Concept

Azure Load Balancer SKU differences and backend pool constraints regarding Availability Zones.
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Topics

Configure Azure Load Balancer

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