Azure Load Balancers

Azure Load Balancer is a Layer 4 (TCP, UDP) load balancer that enables you to distribute network traffic to applications. It provides high availability and network scalability for your applications.

What is Azure Load Balancer?

Azure Load Balancer provides load balancing for IPv4 and IPv6. It distributes inbound traffic among a pool of backend resources, such as virtual machines, virtual machine scale sets, and managed and unmanaged disks. The load balancer can operate at the Standard and Basic tiers. Each tier offers different capabilities and pricing.

Key Features:

  • High Availability: Distributes traffic to ensure continuous operation of your applications.
  • Scalability: Handles fluctuating traffic demands by scaling your backend resources.
  • Layer 4 Load Balancing: Operates at the transport layer, supporting TCP and UDP protocols.
  • Health Probes: Monitors the health of backend instances and routes traffic only to healthy ones.
  • Port Forwarding: Allows direct access to specific services running on backend instances.
  • Outbound Connectivity: Provides outbound connectivity for virtual machines.

Types of Azure Load Balancer

Azure Load Balancer comes in two main types:

  • Standard Load Balancer: Offers advanced features such as Availability Zones support, enhanced diagnostics, and support for multiple public IP addresses. It's recommended for production workloads.
  • Basic Load Balancer: A cost-effective option for less critical workloads, offering basic load balancing capabilities.

How Azure Load Balancer Works

When a client sends a request to a load-balanced endpoint, the Azure Load Balancer receives the request and applies load-balancing rules. These rules determine which backend instance the request should be sent to. Health probes are continuously sent to the backend instances to ensure they are responsive. If an instance fails a health probe, it's temporarily removed from the pool of available resources until it becomes healthy again.

Configuration Steps:

  1. Create a Load Balancer: Choose between Standard or Basic tier.
  2. Configure a Backend Pool: Add the virtual machines or other resources that will serve traffic.
  3. Define Health Probes: Specify how the load balancer will check the health of backend instances.
  4. Set Up Load Balancing Rules: Map frontend IP addresses and ports to backend pools and ports.
  5. Configure NAT Rules (Optional): For direct inbound access to specific services.

Scenarios

Azure Load Balancer is ideal for various scenarios, including:

  • Load balancing web servers for high availability.
  • Distributing traffic for stateless applications.
  • Providing outbound connectivity for VMs in a virtual network.
  • Implementing internal load balancing for private networks.

Example Configuration Snippet (Azure CLI)


az network lb create \
    --resource-group MyResourceGroup \
    --name MyLoadBalancer \
    --sku Standard \
    --public-ip-address MyPublicIP \
    --frontend-ip-name MyFrontendIP \
    --backend-pool-name MyBackendPool

For more in-depth information, please refer to the Advanced Configuration Guide or the Troubleshooting Guide.