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Difficulty: MediumDesign Traffic Routing and Failover Strategies

An enterprise is designing a global business continuity solution for a web application deployed in the East US and West US regions. The architecture must meet the following requirements:

- Route incoming HTTP/HTTPS requests to the region with the lowest latency.
- Provide automatic failover within 30 seconds if a regional endpoint becomes unhealthy.
- Support URL path-based routing (such as routing /images/* to a storage account and /api/* to web servers) at the global entry point.
- Avoid failover delays caused by client-side DNS caching or ISP DNS time-to-live (TTL) configurations.

Which traffic routing and failover service should you recommend?

  1. A
    Azure Traffic Manager configured with priority routing
  2. B
    Azure Cross-Region Load Balancer
  3. Azure Front DoorAnswer
  4. D
    Azure Application Gateway configured with a globally shared public IP address

Answer

Azure Front Door
Azure Front Door is the correct choice because it is a global Layer 7 load balancer that uses Anycast DNS and splits TCP connections to route traffic to the closest healthy backend. Because it operates at Layer 7, it natively supports SSL offloading and URL path-based routing. Additionally, because failover occurs at the Anycast edge POPs rather than via client DNS updates, it avoids delays caused by client-side or ISP DNS caching, enabling failover in less than 30 seconds.

Step-by-Step Solution

1
Analyze the protocol and layer requirements of the workload.
The application requires HTTP/HTTPS routing, SSL offloading, and URL path-based routing, which are Layer 7 features.
This rules out Layer 4 routing options like Azure Cross-Region Load Balancer and DNS-based routing like Azure Traffic Manager.
2
Evaluate failover SLA and DNS caching constraints.
The solution must guarantee failover within 30 seconds and bypass client-side DNS caching.
Anycast-based routing (Azure Front Door) routes traffic directly to the nearest edge POP, where failover is handled immediately without waiting for client-side DNS record expiration.
3
Compare regional vs global scope of the remaining Layer 7 services.
Azure Front Door operates globally, whereas Azure Application Gateway is a regional service.
Since the application is deployed across East US and West US, a global load balancer like Azure Front Door is required to handle traffic distribution and failover.

Key Concept

Azure Front Door is a global Layer 7 load balancer that uses Anycast-based routing to provide low-latency routing, path-based routing, and fast failover that is immune to DNS caching issues.
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Design Traffic Routing and Failover Strategies

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