Introduction

• Explain the core concept of a load balancer and how it acts as a traffic cop, distributing incoming network requests to backend resources to maintain reliability and consistent performance as demand varies.
• Identify and compare the primary Azure load balancing solutions:
  • Azure Load Balancer — Layer 4 (transport) scenarios for TCP/UDP traffic.
  • Application Gateway — Layer 7 (HTTP/HTTPS) routing with web application features such as WAF.
  • Traffic Manager — DNS-based global routing for geographic or performance-based failover.
  • Azure Front Door — global HTTP/HTTPS load balancing, acceleration, and edge features.
• Choose the right Azure service based on application requirements (traffic type, availability, latency, and architectural constraints).

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Load balancing fundamentals

• Increase application availability by avoiding single points of failure.
• Improve performance by distributing load and enabling horizontal scaling.
• Provide fault tolerance and allow graceful handling of instance failures.

• Front-end: The public (or internal) IP and port where clients connect.
• Back-end pool: The set of VMs, VM scale sets, App Service instances, or endpoints that receive traffic.
• Health probes: Periodic checks that determine whether a backend instance is healthy and can receive traffic.
• Session affinity (sticky sessions): Optional configuration to route a client consistently to the same backend.

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Azure load balancing services at a glance

• Azure Load Balancer
  • Layer: 4 (TCP/UDP)
  • Use case: High-performance, low-latency distribution for non-HTTP/S workloads (or for internal VMs).
  • Features: Public and internal SKUs, cross-zone HA, NAT rules.
• Application Gateway
  • Layer: 7 (HTTP/HTTPS)
  • Use case: Web traffic routing with URL-based routing, cookie-based affinity, and WAF integration.
  • Features: Web Application Firewall (WAF), SSL termination, path-based routing.
• Traffic Manager
  • Layer: DNS-based routing
  • Use case: Global traffic distribution using DNS for geographic routing, failover, or performance-based routing.
  • Features: No direct data plane — uses DNS responses to steer clients to endpoints.
• Azure Front Door
  • Layer: Global HTTP/HTTPS (edge)
  • Use case: Global web application acceleration, TLS termination at the edge, dynamic site acceleration, and global load balancing.
  • Features: CDN-like caching, WAF, fast failover across regions, anycast.

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Comparison table

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When to pick each service

• Choose Azure Load Balancer when:
  • You need high-performance Layer 4 routing (TCP/UDP).
  • Your application is non-HTTP (e.g., gaming, databases, custom TCP services).
  • You require an internal (private) load balancer for VNet scenarios.
• Choose Application Gateway when:
  • You need advanced Layer 7 features (URL routing, host-based routing).
  • You want integrated Web Application Firewall (WAF) for OWASP protection.
  • You require SSL termination and session affinity for HTTP-based services.
• Choose Traffic Manager when:
  • You need DNS-level global routing or geographic failover for multi-region deployments.
  • You want to control endpoint selection by latency, priority, or geographic location.
  • Your application can tolerate DNS-based routing behavior and TTL propagation.
• Choose Azure Front Door when:
  • You want global HTTP/HTTPS acceleration (edge caching and routing).
  • You need fast global failover and front-door features such as TLS termination at the edge.
  • Your focus is on low-latency global delivery for web applications and APIs.

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Common architecture patterns

• Internal application (microservices) within a VNet:
  • Use Azure Load Balancer (internal) to distribute TCP traffic to VM Scale Sets or Kubernetes nodes.
• Public web application requiring WAF and URL routing:
  • Use Application Gateway with WAF SKU; place back-end pools as VM Scale Sets, App Service Environments, or AKS Ingress.
• Global web application with low-latency requirements:
  • Use Azure Front Door to direct users to the closest region and provide edge caching. Combine with regional Application Gateways for centralized WAF policies.
• Multi-region failover and geolocation-based routing:
  • Use Traffic Manager to control DNS responses based on performance or geography, optionally combined with Front Door for HTTP acceleration.

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Practical checklist before choosing

• Identify the traffic type: HTTP/HTTPS vs TCP/UDP.
• Determine scope: regional vs global.
• Decide on security needs: Do you need WAF?
• Consider latency and acceleration needs: edge caching, TLS at edge?
• Plan for failover: DNS-based vs application-layer health checks.
• Verify SLA and limits for the chosen SKU.

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References and further reading

• Azure Load Balancer overview (Microsoft Docs)
• Azure Application Gateway overview (Microsoft Docs)
• Azure Traffic Manager overview (Microsoft Docs)
• Azure Front Door overview (Microsoft Docs)
• Kubernetes ingress options on Azure