Azure Internal Load Balancer (ILB)

  Azure Internal Load Balancer (ILB) is a networking service in Microsoft Azure that distributes network traffic to resources within a virtual network. Unlike Azure's public load balancer, which manages external traffic, an ILB is used for internal network traffic within a virtual network. It provides high availability and scalability for applications running in a private network environment. Here are key features and use cases of Azure Internal Load Balancers:

Features and Characteristics:

  1. Internal Load Balancing: ILB is designed to balance traffic within a virtual network or a cloud service, making it an essential component for creating highly available and scalable internal applications.
  2. Private IP Addresses: ILB is associated with private IP addresses, allowing it to route traffic privately within a virtual network without exposure to the public internet.
  3. Layer 4 Load Balancing: ILB operates at Layer 4 (Transport layer) of the OSI model, forwarding traffic based on TCP/UDP port and protocol. It does not inspect application content.
  4. TCP and UDP Protocols: ILB supports both TCP and UDP traffic, making it suitable for a wide range of applications and services.
  5. High Availability: ILB distributes traffic across multiple virtual machines (VMs) or instances to ensure high availability and fault tolerance. If one VM fails, traffic is automatically routed to healthy instances.
  6. Session Persistence: ILB supports session affinity (also known as client IP affinity or sticky sessions) to ensure that related traffic from a single client is routed to the same VM for the duration of a session.

Use Cases:

  1. Application High Availability: ILB can be used to distribute traffic across multiple VMs running an application to ensure high availability and redundancy. If one VM fails, traffic is redirected to the healthy VMs.
  2. Database Clustering: ILB is often used with database clusters, such as SQL Server Always On Availability Groups, to distribute client connections among database replicas for improved performance and fault tolerance.
  3. Private Web Services: When hosting web services or APIs for internal use within your organization, ILB ensures that traffic remains within the corporate network, enhancing security.
  4. Internal Load Balanced Sets: You can define load-balanced sets in Azure VMs and associate them with an ILB to distribute traffic to specific ports on the VMs.
  5. Multi-Tier Applications: ILB can be part of multi-tier application architectures, routing traffic between front-end, middle-tier, and back-end VMs while maintaining network isolation.

To set up an Azure Internal Load Balancer, you'll typically create a load balancer resource, define frontend and backend IP configurations, configure load balancing rules, and associate it with the target VMs or instances. This ensures that the ILB effectively routes traffic to the appropriate resources in your private virtual network.

Overall, Azure Internal Load Balancers are a powerful tool for ensuring the availability, scalability, and security of internal applications and services within your Azure virtual network.


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