Why Traffic Failover Matters
Even if databases and storage are resilient, users must still connect to applications during outages. Global businesses often require intelligent traffic routing and failover to keep apps responsive and available worldwide.
Azure provides multiple services to handle traffic distribution, failover, and global reach: Traffic Manager, Front Door, and Load Balancers.
1. Azure Traffic Manager
Definition:
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DNS-based global traffic routing service.
Key Features:
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Routes users to closest or healthiest endpoint.
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Routing methods: priority, weighted, geographic, performance, multi-value, subnet.
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Works at the DNS level (users resolve to endpoint IP).
Best Use Cases:
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Global failover between regions (e.g., East US ↔ West US).
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Geo-routing for compliance (EU users → EU region).
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Priority-based DR (primary → secondary on failure).
2. Azure Front Door
Definition:
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Global, edge-based load balancer + application accelerator.
Key Features:
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Layer 7 routing (HTTP/HTTPS).
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Anycast routing for low latency worldwide.
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Built-in WAF (Web Application Firewall).
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Caching and acceleration like CDN.
Best Use Cases:
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High-performance global websites.
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Apps requiring SSL offloading and edge routing.
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Multi-region failover with global distribution.
3. Azure Load Balancers
Types:
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Azure Load Balancer (Layer 4): TCP/UDP traffic across VMs.
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Application Gateway (Layer 7): Web traffic routing, SSL termination, path-based routing.
Best Use Cases:
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Regional load distribution across VMs.
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Protect web apps with WAF (via App Gateway).
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Internal load balancing for backend tiers.
Design Considerations
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Traffic Manager → Best for DNS-based failover, compliance routing.
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Front Door → Best for global web distribution + performance optimization.
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Load Balancer → Best for regional VM load distribution.
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App Gateway → Best for web app routing with WAF.
Best Practice: Combine them.
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Use Traffic Manager for DNS-level failover.
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Use Front Door for global web distribution and caching.
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Use App Gateway + Load Balancer for regional traffic management.
Example Enterprise Scenario
A multinational retailer requires:
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Web traffic routed to closest healthy region.
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Global users must experience low latency.
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Failover to secondary region if primary goes down.
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Protection from SQL injection and XSS attacks.
Correct design:
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Use Traffic Manager for DNS failover across regions.
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Use Front Door for global routing and edge acceleration.
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Deploy App Gateway with WAF for application-level protection in each region.
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Use Load Balancer to distribute traffic across VMs in regional tiers.
Confusion Buster
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Traffic Manager vs Front Door
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TM = DNS-based, directs to endpoints.
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Front Door = edge-based, directs to closest edge + provides acceleration.
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Front Door vs CDN
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FD = load balancing + acceleration.
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CDN = static content caching only.
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Load Balancer vs App Gateway
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LB = Layer 4, transport-level traffic.
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AppGW = Layer 7, web app traffic with WAF.
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Exam Tips
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“Which Azure service routes users to closest region at DNS level?” → Traffic Manager.
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“Which service accelerates global apps with edge routing?” → Front Door.
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“Which distributes TCP/UDP traffic across VMs in a region?” → Load Balancer.
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“Which protects apps against SQL injection and XSS?” → Application Gateway (WAF).
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“Which combo for global failover + app security?” → Traffic Manager + Front Door + App Gateway.
What to Expect in the Exam
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Direct Q: “Which service provides DNS-based global failover?” → Traffic Manager.
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Scenario Q: “Company wants to accelerate global e-commerce site with low latency.” → Front Door.
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Scenario Q: “Company requires multi-region failover with compliance routing.” → Traffic Manager.
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Trick Q: “Load Balancer can do SSL offloading.” → False (App Gateway does).