Microsoft Azure Documentation

Azure Load Balancing: Distribute Traffic Effectively

Azure Load Balancer is a high-performance, highly available load balancing service that distributes inbound and outbound traffic to applications and services. It operates at Layer 4 (TCP/UDP) of the OSI model and provides a robust solution for ensuring application availability and scalability.

Types of Load Balancers in Azure

Azure offers several load balancing solutions to meet different needs:

• Azure Load Balancer: The core Layer 4 load balancer for internal and external traffic.
  • Standard SKU: Offers advanced features like zone redundancy, NAT rules, and health probes.
  • Basic SKU: Suitable for less critical workloads with simpler requirements.
• Azure Application Gateway: A Layer 7 (HTTP/HTTPS) load balancer that provides advanced routing capabilities, SSL termination, and Web Application Firewall (WAF) integration.
• Azure Front Door: A global, scalable entry point that uses the Microsoft global edge network to create fast, secure, and widely scalable web applications.

How Azure Load Balancer Works

Azure Load Balancer uses a 5-tuple hash-based distribution algorithm to distribute network traffic. The flow is distributed based on:

• Source IP address
• Source port
• Destination IP address
• Destination port
• Protocol type

Health probes are crucial for determining the health of backend instances. If an instance fails a health probe, the load balancer stops sending traffic to it until it becomes healthy again.

Configuring Azure Load Balancer

Creating and configuring an Azure Load Balancer typically involves the following steps:

1. Create a Load Balancer resource in the Azure portal or via Azure CLI/PowerShell.
2. Configure a Frontend IP configuration to define the public or internal IP address that receives traffic.
3. Create a Backend pool containing the virtual machines or virtual machine scale sets that will serve the traffic.
4. Define a Health probe to monitor the health of backend instances.
5. Configure a Load balancing rule to map incoming traffic to the backend pool, specifying ports and protocols.
6. (Optional) Configure NAT rules for direct inbound access to specific VMs.

Example Configuration Snippet (Conceptual):

{
  "name": "myLoadBalancer",
  "location": "East US",
  "sku": {
    "name": "Standard"
  },
  "frontendIpConfigurations": [
    {
      "name": "myFrontend",
      "properties": {
        "publicIpAddress": {
          "id": "/subscriptions/.../resourceGroups/.../providers/Microsoft.Network/publicIPAddresses/myPublicIP"
        }
      }
    }
  ],
  "backendAddressPools": [
    {
      "name": "myBackendPool",
      "properties": {
        "backendIPConfigurations": []
      }
    }
  ],
  "loadBalancingRules": [
    {
      "name": "myHTTPRule",
      "properties": {
        "frontendIpConfiguration": {
          "id": "/subscriptions/.../resourceGroups/.../providers/Microsoft.Network/loadBalancers/myLoadBalancer/frontendIPConfigurations/myFrontend"
        },
        "backendAddressPool": {
          "id": "/subscriptions/.../resourceGroups/.../providers/Microsoft.Network/loadBalancers/myLoadBalancer/backendAddressPools/myBackendPool"
        },
        "protocol": "Tcp",
        "frontendPort": 80,
        "backendPort": 80,
        "enableFloatingIP": false,
        "idleTimeoutInMinutes": 4,
        "disableOutboundSnat": false,
        "provisioningState": "Succeeded"
      }
    }
  ]
}
                

Best Practices

• Use Standard SKU for production workloads.
• Configure appropriate health probes to ensure high availability.
• Leverage zone redundancy for critical applications.
• Consider Application Gateway or Front Door for HTTP/S specific needs.
• Monitor load balancer metrics for performance and availability.

For detailed configuration guides and advanced scenarios, please refer to the official Azure Load Balancer documentation.