⚡ Azure Load Balancer – Distributing Traffic Across Multiple Virtual Machines

In today’s cloud-first world, ensuring high availability, scalability, and fault tolerance for applications is critical. Traffic spikes, unexpected VM failures, and uneven load distribution can negatively impact user experience.

Azure Load Balancer (ALB) is Microsoft Azure’s Layer 4 load balancing service designed to distribute incoming network traffic across multiple Virtual Machines (VMs) or services in a region. By distributing workloads efficiently, Azure Load Balancer ensures applications are highly available and resilient.

Whether you’re running a single-tier web app or a multi-tier enterprise application, understanding and implementing Azure Load Balancer is essential for architects, developers, and cloud professionals.

🔹 What is Azure Load Balancer?

Azure Load Balancer is a Layer 4 (TCP/UDP) load balancer that allows you to:

• Distribute incoming traffic across multiple VMs or services.
• Increase availability and reliability for your applications.
• Support both internal (private) and external (public) load balancing.
• Handle high volumes of traffic with ultra-low latency.

Azure Load Balancer comes in two SKUs:

1. Basic Load Balancer – For dev/test scenarios, supports up to 100 instances, and no SLA.
2. Standard Load Balancer – For production, higher scale, built-in SLA, better security and metrics.

🔹 Key Features

• Automatic traffic distribution across healthy VMs.
• Health probes to detect VM failures and reroute traffic.
• Outbound connections for VMs without public IPs.
• High availability through multi-zone deployment.
• Support for TCP, UDP, and HTTP(S) traffic when integrated with Application Gateway.
• Integration with Azure Monitor for metrics and logging.

🔹 How Azure Load Balancer Works

1. Incoming request reaches the Load Balancer (public or internal IP).
2. Health probe checks which backend VMs are healthy.
3. Load Balancer forwards request to available VM using a distribution algorithm (5-tuple hash: source IP, source port, destination IP, destination port, protocol).
4. VM processes request and response returns to client.

🔹 Types of Azure Load Balancer

🔹 3 Unique Example Programs for Azure Load Balancer

✅ Example 1: Create a Public Load Balancer via Azure CLI

# Create a Resource Group
az group create --name MyResourceGroup --location eastus

# Create a public IP for the load balancer
az network public-ip create --resource-group MyResourceGroup --name MyPublicIP --sku Standard

# Create the Load Balancer
az network lb create \
  --resource-group MyResourceGroup \
  --name MyLoadBalancer \
  --sku Standard \
  --public-ip-address MyPublicIP \
  --frontend-ip-name MyFrontEnd \
  --backend-pool-name MyBackEndPool

# Create a health probe
az network lb probe create \
  --resource-group MyResourceGroup \
  --lb-name MyLoadBalancer \
  --name MyHealthProbe \
  --protocol tcp \
  --port 80

# Create a load balancing rule
az network lb rule create \
  --resource-group MyResourceGroup \
  --lb-name MyLoadBalancer \
  --name MyHTTPRule \
  --protocol tcp \
  --frontend-port 80 \
  --backend-port 80 \
  --frontend-ip-name MyFrontEnd \
  --backend-pool-name MyBackEndPool \
  --probe-name MyHealthProbe

👉 This example distributes HTTP traffic across backend VMs with automatic health monitoring.

✅ Example 2: Create an Internal Load Balancer with PowerShell

# Create backend subnet
$subnet = New-AzVirtualNetworkSubnetConfig -Name BackendSubnet -AddressPrefix 10.0.1.0/24

# Create VNet
$vnet = New-AzVirtualNetwork -ResourceGroupName MyResourceGroup -Name MyVNet -Location eastus -AddressPrefix 10.0.0.0/16 -Subnet $subnet

# Create Internal Load Balancer
$frontendIP = New-AzLoadBalancerFrontendIpConfig -Name MyFrontEnd -SubnetId $vnet.Subnets[0].Id -PrivateIpAddress 10.0.1.4

$backendPool = New-AzLoadBalancerBackendAddressPoolConfig -Name MyBackEndPool

$probe = New-AzLoadBalancerProbeConfig -Name MyHealthProbe -Protocol Tcp -Port 8080 -IntervalInSeconds 15 -ProbeCount 2

New-AzLoadBalancer -ResourceGroupName MyResourceGroup -Name MyILB -Sku Standard -FrontendIpConfiguration $frontendIP -BackendAddressPool $backendPool -Probe $probe

👉 This creates a private load balancer to distribute traffic inside a VNet.

✅ Example 3: ARM Template for Load Balancer Deployment

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "resources": [
    {
      "type": "Microsoft.Network/loadBalancers",
      "apiVersion": "2021-05-01",
      "name": "myLoadBalancer",
      "location": "eastus",
      "sku": { "name": "Standard" },
      "properties": {
        "frontendIPConfigurations": [
          {
            "name": "MyFrontEnd",
            "properties": { "publicIPAddress": { "id": "[resourceId('Microsoft.Network/publicIPAddresses','myPublicIP')]" } }
          }
        ],
        "backendAddressPools": [{ "name": "MyBackEndPool" }],
        "probes": [{ "name": "MyHealthProbe", "properties": { "protocol": "Tcp", "port": 80, "intervalInSeconds": 15, "numberOfProbes": 2 } }],
        "loadBalancingRules": [
          {
            "name": "MyHTTPRule",
            "properties": {
              "frontendIPConfiguration": { "id": "[concat(resourceId('Microsoft.Network/loadBalancers','myLoadBalancer'),'/frontendIPConfigurations/MyFrontEnd')]" },
              "backendAddressPool": { "id": "[concat(resourceId('Microsoft.Network/loadBalancers','myLoadBalancer'),'/backendAddressPools/MyBackEndPool')]" },
              "protocol": "Tcp",
              "frontendPort": 80,
              "backendPort": 80,
              "probe": { "id": "[concat(resourceId('Microsoft.Network/loadBalancers','myLoadBalancer'),'/probes/MyHealthProbe')]" }
            }
          }
        ]
      }
    }
  ]
}

👉 This Infrastructure as Code approach ensures reproducibility and version control.

🎯 How to Remember Azure Load Balancer (Interview & Exam Prep)

Use the mnemonic “F.R.O.H.”

• F – Frontend IP: Where traffic arrives
• R – Rules: Direct traffic to backend VMs
• O – Outbound connections: Manage VM internet access
• H – Health probes: Detect VM availability

Remember: “FRoH keeps your traffic flowing healthy”

📘 Why It’s Important to Learn Azure Load Balancer

1. High Availability: Essential for production workloads.
2. Scalability: Automatically distributes traffic during spikes.
3. Security Integration: Works with NSGs, Azure Firewall, and Application Gateway.
4. Certification & Career: Core topic in AZ-104, AZ-305, and Azure DevOps exams.
5. Real-world Relevance: Used in multi-tier apps, microservices, and hybrid cloud setups.

📊 Real-World Use Cases

• Web Applications: Evenly distribute HTTP requests across VMs.
• Multi-Tier Architecture: Frontend VMs balanced for high availability, backend VMs isolated.
• Gaming: Multiplayer games with low-latency traffic distribution.
• IoT Applications: Balance connections from thousands of devices.
• Hybrid Cloud: Internal load balancing between on-premises and cloud services.

📝 Best Practices

• Use Standard SKU for production for SLA and scale.
• Always configure health probes for backend VM monitoring.
• Combine Load Balancer + NSG + Azure Firewall for security.
• Use ARM templates or CLI scripts for repeatable deployments.
• Consider zones for high availability.

🔹 Conclusion

Azure Load Balancer is a critical networking service for ensuring that applications are highly available, scalable, and reliable.

Key takeaways:

• Understand Frontend IP, Backend Pool, Health Probes, and Rules.
• Use CLI, PowerShell, or ARM templates to deploy and manage Load Balancers.
• Remember “F.R.O.H.” for exams and interviews.
• Apply best practices to ensure high availability and security.

Mastering Azure Load Balancer prepares you for real-world architecture design, Azure certifications, and enterprise cloud deployments.