Microsoft Certified: Azure Administrator AssociateImplement and manage virtual networkingMedium
A company is deploying a new application that consists of several stateless web servers. These web servers need to be scaled automatically based on demand and must be accessible from the internet. To ensure high availability and efficient distribution of incoming HTTP traffic, an Azure Application Gateway is configured. The backend pool of the Application Gateway needs to dynamically include new web server instances as they scale out. Which type of backend pool target should be used for the Application Gateway?
- AApp Services
- BIP address or FQDN
- CVirtual machine scale set
- DVirtual machine
Show answer & explanationAnswer & explanation
Correct answer: C. Virtual machine scale set
Virtual Machine Scale Sets (VMSS) are designed for autoscaling and load balancing of identical VMs. When a VMSS is used as a backend pool target, Application Gateway automatically detects and adds/removes instances as the scale set scales in or out, ensuring dynamic and efficient traffic distribution.
Why the other options are wrong
- A. App Services are a platform-as-a-service offering. While they can be backend targets, the question specifically refers to 'stateless web servers' implying IaaS VMs that scale, making VMSS the more direct and appropriate answer for this scenario.
- B. Using explicit IP addresses or FQDNs would require manual updates to the backend pool as instances scale, which is not dynamic.
- D. Referencing individual virtual machines would also require manual updates and doesn't inherently support dynamic scaling.
Application Gateway Backend Pool
A collection of backend targets (VMs, VMSS, IP addresses, App Services) that receive traffic from the Application Gateway.
- Supports various backend target types.
- VMSS provides dynamic scaling integration.
- Health probes monitor backend health.
Memory trick: VMSS for auto-scale, IP for static, App Service for PaaS.