Documentation

Introduction to Azure Load Balancing

This document provides an overview of load balancing solutions available within Microsoft Azure. Load balancing is a critical component for building resilient, highly available, and scalable applications. It distributes incoming network traffic across multiple backend resources, such as virtual machines or containers, ensuring that no single resource is overwhelmed and improving overall application performance and reliability.

Why Use Load Balancing?

  • High Availability: By distributing traffic, if one instance fails, others can continue to serve requests, preventing downtime.
  • Scalability: Load balancers allow you to scale your application horizontally by adding more instances behind the load balancer.
  • Performance: Distributing the load helps reduce latency and improve response times for users.
  • Health Monitoring: Most load balancing solutions include health probes to detect unhealthy instances and route traffic away from them.

Azure Load Balancing Services

Azure offers a variety of load balancing services, each suited for different scenarios:

  • Azure Load Balancer: A Layer 4 (TCP/UDP) load balancer that provides high performance and low latency. It's ideal for load balancing network traffic to virtual machines within an Azure region.
  • Azure Application Gateway: A Layer 7 (HTTP/HTTPS) load balancer that offers advanced routing capabilities based on request attributes like URL path, host headers, and more. It's perfect for web applications.
  • Azure Front Door: A global, scalable entry point that uses the Microsoft global edge network to create fast, secure, and widely scalable web applications. It offers features like SSL offloading, cookie-based session affinity, and URL path-based routing.
  • Azure Traffic Manager: A DNS-based traffic load balancer that enables you to distribute traffic optimally to your services, whether they are deployed in Azure or on-premises.
Key Takeaway: Understanding the differences between these services is crucial for selecting the right solution for your application's specific needs.

Core Concepts in Load Balancing

Regardless of the specific Azure service you choose, several fundamental concepts apply:

  • Load Balancing Rules: Define how incoming traffic is distributed to backend resources.
  • Health Probes: Periodically check the health of backend instances to ensure they are responsive.
  • Backend Pools: A collection of backend resources (e.g., VMs, VM Scale Sets) that will receive traffic from the load balancer.
  • Session Affinity (Sticky Sessions): A feature that directs all requests from a particular client to the same backend server.
Pro Tip: Always configure health probes that accurately reflect the readiness of your application to serve traffic.

This documentation will guide you through each of these Azure load balancing services, their features, configurations, and best practices to help you build robust and performant cloud solutions.

Important: Azure Load Balancer is a regional service, while Azure Front Door is a global service. This distinction significantly impacts how you design for disaster recovery and global traffic management.