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Difficulty: MediumDesign Traffic Routing and Failover Strategies

A company hosts a global web application across the North Europe and East US regions. During testing of a disaster recovery scenario, the team notices that when they simulate a regional outage, some external clients continue to send traffic to the failed region for several minutes. Investigation reveals that these clients ignore the low Time-to-Live (TTL) settings on DNS records. The company wants to migrate to a global routing solution that eliminates reliance on client-side DNS caching and provides SSL termination at the edge. Which Azure service should you recommend to meet these requirements?

  1. Azure Front DoorAnswer
  2. B
    Azure Traffic Manager
  3. C
    Azure Application Gateway
  4. D
    Azure Load Balancer

Answer

Azure Front Door
Azure Front Door uses Anycast routing to advertise a single virtual IP address globally. When a regional backend fails, Front Door updates its internal routing path and directs subsequent requests to the healthy region over the Microsoft backbone. The client's connection point remains the same, eliminating failover latency introduced by client-side DNS caching. It also natively supports SSL termination.

Step-by-Step Solution

1
Identify the primary root cause of the failover delay, which is client-side DNS caching behavior that ignores TTL settings.
This rules out DNS-based traffic routing solutions such as Azure Traffic Manager.
DNS-based solutions rely on the client resolving DNS records to find new endpoints, which fails if the client caches the previous endpoint IP.
2
Evaluate the remaining global and regional routing options against the need for global routing and SSL termination.
This rules out regional solutions like Azure Application Gateway and Layer 4 solutions like Azure Load Balancer.
Application Gateway cannot route between multiple regions natively, and Load Balancer cannot perform SSL termination at the edge.
3
Select the service that utilizes Anycast-based routing and operates at Layer 7.
Azure Front Door is chosen.
Azure Front Door uses Anycast routing to handle client connections at the nearest edge PoP and routes traffic across the Microsoft network, avoiding client DNS updates during a backend failover.

Key Concept

Contrasting Anycast-based routing (Azure Front Door) with DNS-based routing (Azure Traffic Manager) for global failover scenario designs.

Alternative Method

Alternatively, you could combine Azure Traffic Manager with regional Azure Application Gateways to achieve path-based routing, but this would still suffer from client-side DNS caching delays during failover, failing the primary requirement.
Estimated Time:1m 30s
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Topics

Design Traffic Routing and Failover Strategies

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