Why load balancing matters in Azure - Why It Works

Introduction

When many people visit a website or app at the same time, the servers can get overwhelmed and slow down or stop working. Load balancing helps by spreading the work evenly across multiple servers so everything runs smoothly and no one server gets too busy.

When your website gets a lot of visitors at once and you want to keep it fast and responsive

When you run an app that needs to be available all the time without interruptions

When you want to make sure your service keeps working even if one server breaks

When you want to add more servers easily to handle growing traffic

When you want to avoid one server doing all the work and getting tired

Commands

This command creates a basic Azure Load Balancer named example-lb in the example-rg resource group. It sets up the frontend IP and backend pool where servers will be added.

Terminal

az network lb create --resource-group example-rg --name example-lb --sku Basic --frontend-ip-name example-frontend --backend-pool-name example-backendpool --location eastus

Expected Output

{

  "frontendIpConfigurations": [

    {

      "name": "example-frontend",

      "privateIpAddress": null,

      "privateIpAllocationMethod": "Dynamic",

      "publicIpAddress": null

    }

  ],

  "backendAddressPools": [

    {

      "name": "example-backendpool"

    }

  ],

  "provisioningState": "Succeeded",

  "resourceGroup": "example-rg",

  "location": "eastus",

  "sku": {

    "name": "Basic"

  },

  "name": "example-lb"

}

→

--resource-group - Specifies the resource group where the load balancer is created

→

--sku - Defines the type of load balancer (Basic or Standard)

This command creates a rule for the load balancer to listen on port 80 (web traffic) and forward it to the backend servers on the same port.

Terminal

az network lb rule create --resource-group example-rg --lb-name example-lb --name example-lbrule --protocol Tcp --frontend-port 80 --backend-port 80 --frontend-ip-name example-frontend --backend-pool-name example-backendpool

Expected Output

{

  "name": "example-lbrule",

  "protocol": "Tcp",

  "frontendPort": 80,

  "backendPort": 80,

  "provisioningState": "Succeeded"

}

→

--protocol - Specifies the network protocol to use (Tcp or Udp)

→

--frontend-port - Port on the load balancer to listen for incoming traffic

→

--backend-port - Port on backend servers to send the traffic

This command adds a virtual machine's network interface (example-nic1) to the load balancer's backend pool so it can receive traffic.

Terminal

az network nic ip-config address-pool add --resource-group example-rg --nic-name example-nic1 --ip-config-name ipconfig1 --lb-name example-lb --address-pool example-backendpool

Expected Output

No output (command runs silently)

→

--nic-name - Specifies the network interface of the VM to add

→

--address-pool - Specifies the backend pool to add the NIC to

This command shows the current configuration and status of the load balancer to verify it is set up correctly.

Terminal

az network lb show --resource-group example-rg --name example-lb

Expected Output

{

  "name": "example-lb",

  "location": "eastus",

  "provisioningState": "Succeeded",

  "frontendIpConfigurations": [

    {

      "name": "example-frontend",

      "privateIpAllocationMethod": "Dynamic"

    }

  ],

  "backendAddressPools": [

    {

      "name": "example-backendpool",

      "backendIpConfigurations": [

        {

          "id": "/subscriptions/xxxx/resourceGroups/example-rg/providers/Microsoft.Network/networkInterfaces/example-nic1/ipConfigurations/ipconfig1"

        }

      ]

    }

  ]

}

Key Concept

If you remember nothing else from this pattern, remember: load balancing spreads user traffic evenly across servers to keep apps fast and reliable.

Common Mistakes

Not adding virtual machines to the backend pool after creating the load balancer

Without backend servers, the load balancer has nowhere to send traffic, so users get errors or no response.

Always add the network interfaces of your servers to the load balancer's backend pool using the correct commands.

Using the wrong ports in the load balancer rule

If the frontend and backend ports don't match the app's listening ports, traffic won't reach the servers correctly.

Set the frontend and backend ports in the load balancer rule to match the ports your app uses, commonly port 80 for web.

Summary

Create an Azure Load Balancer with frontend IP and backend pool to manage traffic.

Set up load balancer rules to forward traffic on specific ports to backend servers.

Add virtual machines to the backend pool so they receive traffic from the load balancer.

Verify the load balancer configuration to ensure it is working as expected.