Azure Load Balancing Documentation

Azure Load Balancing

Azure Load Balancer is a Layer 4 (TCP/UDP) load balancer that enables you to distribute network traffic to applications and services hosted in Azure. It provides high availability and responsiveness for your applications by distributing incoming traffic across multiple virtual machines or instances. Load Balancer operates across Availability Zones, providing resilience.

Key Concepts

Load Balancing Rules: These rules define how traffic is distributed. You can configure rules to specify the front-end IP configuration, protocol, front-end port, back-end port, and the back-end pool to which traffic should be sent.
Health Probes: Health probes are used to monitor the health of the back-end instances. If an instance becomes unhealthy, the load balancer stops sending traffic to it.
Back-end Pools: A back-end pool is a collection of virtual machines or VM Scale Sets that are capable of receiving traffic from the load balancer.
Outbound Rules: These rules allow you to define outbound connectivity for your back-end instances.

Types of Azure Load Balancers

Azure offers different load balancing solutions based on your needs:

Azure Load Balancer: A regional, high-performance, Layer 4 load balancer.
Azure Application Gateway: A Layer 7 (HTTP/HTTPS) load balancer that offers advanced routing capabilities, SSL termination, and Web Application Firewall (WAF) integration.
Azure Traffic Manager: A DNS-based traffic load balancer that allows you to distribute traffic optimally to your Azure and external services.

When to Use Azure Load Balancer

Azure Load Balancer is ideal for scenarios requiring high availability and scalability for applications where traffic distribution at the transport layer (TCP/UDP) is sufficient. It's commonly used for:

Distributing traffic across multiple instances of a virtual machine for stateless applications.
Ensuring application availability even if a single virtual machine or even an entire Availability Zone fails.
Directing traffic to on-premises resources via Azure ExpressRoute or VPN Gateway.

Configuring Load Balancer

You can configure Azure Load Balancer using the Azure portal, Azure CLI, PowerShell, or ARM templates.

Example: Creating a Load Balancer Rule (Azure CLI)


az network lb rule create \
    --resource-group MyResourceGroup \
    --lb-name MyLoadBalancer \
    --name MyHttpRule \
    --protocol Tcp \
    --frontend-port 80 \
    --backend-port 80 \
    --frontend-ip-name MyFrontendIP \
    --backend-pool-name MyBackendPool

Note: For more advanced features like URL-based routing, SSL termination, and WAF, consider using Azure Application Gateway.

Important: Ensure your health probes are configured correctly to accurately reflect the health of your back-end services.

Microsoft Docs