Azure Load Balancer

Introduction to Azure Load Balancer

Azure Load Balancer is a high-performance, low-latency Layer 4 load balancer that distributes incoming traffic across a pool of backend resources, such as virtual machines or virtual machine scale sets. It provides a highly available and scalable solution for your applications.

It operates on TCP and UDP protocols and can handle millions of concurrent connections. Azure Load Balancer is designed to be resilient and fault-tolerant, ensuring your applications remain accessible even during hardware failures.

Diagram illustrating Azure Load Balancer distribution.

Key Features

• High Availability: Ensures your applications are always accessible by distributing traffic and performing health probes.
• Scalability: Automatically scales to handle varying traffic loads.
• Performance: Provides low-latency distribution of traffic.
• Secure: Integrates with Azure security features for comprehensive protection.
• Cost-Effective: Offers a pay-as-you-go pricing model.
• Health Probes: Continuously monitors the health of backend instances to avoid sending traffic to unhealthy ones.
• Session Persistence: Configurable to keep a client connected to the same backend instance.

How Azure Load Balancer Works

Azure Load Balancer works by assigning a public or internal IP address to the load balancer. Incoming network traffic directed to this IP address is then evaluated based on configured load balancing rules.

These rules define how traffic is distributed to backend pool instances. Health probes are essential for maintaining the availability of your application. If a health probe detects that a backend instance is unhealthy, the load balancer will stop sending traffic to that instance until it becomes healthy again.

The process typically involves:

1. A client sends a request to the load balancer's IP address.
2. The load balancer receives the request and checks its configured rules.
3. A health probe verifies the health of the available backend instances.
4. Based on the rules and health probe status, the load balancer selects a healthy backend instance.
5. The load balancer forwards the request to the chosen backend instance.
6. The backend instance processes the request and sends the response directly back to the client (Direct Server Return).

Types of Azure Load Balancers

Azure offers two main types of load balancers:

Common Use Cases

Azure Load Balancer is ideal for a variety of scenarios:

Pricing

Azure Load Balancer pricing is based on the SKU (Basic or Standard) and the number of rules configured. Standard Load Balancer has a higher hourly cost but offers more features and better performance for production environments.

For detailed pricing information, please refer to the official Azure Load Balancer pricing page.

Getting Started with Azure Load Balancer

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

Here's a quick overview of the steps involved:

1. Create a Load Balancer: Choose the SKU (Basic or Standard) and whether it's public or internal.
2. Configure Frontend IP: Assign a public or private IP address to the load balancer.
3. Define Backend Pool: Specify the virtual machines or scale sets that will receive traffic.
4. Create Health Probes: Configure probes to monitor the health of backend instances.
5. Set Up Load Balancing Rules: Define rules that map frontend ports and protocols to backend ports and protocols.

You can find comprehensive step-by-step guides in the official Azure documentation:

• Quickstart: Load balance VMs with a Standard Public Load Balancer using Azure CLI
• Tutorial: Load balance VMs with an internal load balancer using the Azure portal