Azure External Load Balancer

 Azure External Load Balancer(public) is a network service provided by Microsoft Azure that distributes incoming internet traffic across multiple virtual machines (VMs) or instances in a backend pool. It is designed to improve the availability and scalability of applications and services that are exposed to the public internet. Here are key features and use cases for Azure External Load Balancer:

Features and Characteristics:

1. Public IP Address: Azure External Load Balancer is associated with a public IP address (VIP - Virtual IP address) that clients use to access your application or service.
2. Layer 4 Load Balancing: It operates at Layer 4 (Transport layer) of the OSI model, routing traffic based on TCP/UDP port and protocol. It does not inspect application content.
3. TCP and UDP Protocols: Azure External Load Balancer supports both TCP and UDP traffic, making it suitable for a wide range of applications and services.
4. Load Balancing Rules: You can configure load balancing rules that define how incoming traffic is distributed to the VMs in the backend pool. Rules include port numbers, protocols, and session persistence settings.
5. Health Probes: The load balancer periodically checks the health of VM instances in the backend pool using health probes. Unhealthy instances are temporarily removed from the rotation until they become healthy again.
6. Outbound Connections: It supports outbound connections from the VMs to the internet, allowing VMs to communicate with external resources.
7. High Availability: Azure External Load Balancer is designed for high availability and fault tolerance. If a VM or instance becomes unhealthy or fails, traffic is automatically routed to healthy instances.
8. Session Persistence: It 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 backend VM for the duration of a session.

Use Cases:

1. Web Applications: Azure External Load Balancer is commonly used to distribute traffic to web applications and APIs hosted on multiple VMs. It ensures that the application remains available and responsive, even if one or more VMs fail.
2. Public-Facing Services: It's suitable for public-facing services, such as websites, e-commerce platforms, and RESTful APIs, that need to handle a large volume of incoming internet traffic.
3. Internet-Facing Applications: Azure External Load Balancer can be part of multi-tier application architectures, serving as the entry point for internet-facing services while maintaining network isolation.
4. Application Redundancy: For critical applications, multiple VM instances can be deployed across different availability zones or regions, and Azure External Load Balancer can distribute traffic to these instances for geographic redundancy.
5. Hybrid Cloud: It can be used to distribute traffic between on-premises data centers and Azure resources in a hybrid cloud setup.

Setting up Azure External Load Balancer typically involves creating a load balancer resource, defining frontend and backend IP configurations, configuring load balancing rules, and associating the backend pool with VM instances. This ensures that the load balancer effectively routes incoming internet traffic to the appropriate VMs, improving application availability and scalability.

In summary, Azure External Load Balancer is a key component in building scalable and highly available internet-facing applications and services on the Azure cloud platform.