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Azure Load Balancer is a service provided by Microsoft Azure designed to distribute incoming network traffic across multiple virtual machines (VMs) or other resources to ensure high availability and reliability. It operates at the Layer 4 (Transport Layer) of the OSI model and is crucial for maintaining performance and scaling applications in the cloud.

Azure Load Balancer offers two main types: Basic and Standard. The Basic Load Balancer is suitable for smaller applications with simpler needs, while the Standard Load Balancer provides advanced features and higher performance for larger, more complex deployments. The Standard Load Balancer offers enhanced security, better performance, and additional features like zone redundancy.

Azure Load Balancer supports various features including:

• Azure Automatic Traffic Distribution: Distributes inbound traffic across multiple VMs or instances to ensure no single resource is overwhelmed.
• Azure Health Probes: Continuously monitors the health of instances using probes to ensure traffic is only sent to healthy resources.
• Azure Inbound and Outbound Rules: Configurable rules for handling incoming and outgoing traffic, including NAT (Network Address Translation) rules for public IP addresses.
• Azure High Availability: Ensures the availability of applications by distributing traffic across multiple resources and providing redundancy.

Azure Load Balancer can be configured and managed through the Azure portal, Azure CLI, Azure Resource Manager (ARM) templates or Azure Bicep. Users can set up load balancing rules, configure health probes, and define backend pools consisting of VMs or other resources. Configuration options allow for fine-tuning the load balancing behavior to meet specific application needs.

Azure Load Balancer integrates seamlessly with other Azure services, including Azure Virtual Machine Scale Sets (VMSS), Azure Application Gateway, and Azure Traffic Manager. These integrations help to enhance load balancing capabilities, improve application performance, and provide more comprehensive traffic management solutions.

Azure Load Balancer is designed to handle large volumes of traffic and scale automatically to accommodate varying workloads. It supports millions of concurrent connections and can balance traffic across large numbers of instances, ensuring high performance and reliability for applications.

Security is a key aspect of Azure Load Balancer. It integrates with Azure Network Security Groups (NSGs) to control inbound and outbound traffic based on security rules. Users can also configure rules to restrict access and protect their applications from unauthorized or malicious traffic.

Azure provides various tools for monitoring and troubleshooting Azure Load Balancer, including Azure Monitor and Azure Network Watcher. These tools help users diagnose issues, view traffic metrics, and ensure that load balancing operations are functioning correctly.

Azure Load Balancer pricing is based on the type of load balancer, the number of rules and data processing units (DPU) used, and the amount of outbound data processed. Effective cost management involves understanding these pricing components and optimizing the configuration to balance performance and cost.

To optimize the use of Azure Load Balancer, users should follow best practices such as configuring appropriate health probes, regularly reviewing load balancing rules, and monitoring traffic patterns. Proper setup and ongoing management help ensure that applications remain available and perform well.

Future updates to Azure Load Balancer may include enhanced features and capabilities driven by advances in cloud technology. These developments could include improved analytics, more sophisticated load balancing algorithms, and better integration with emerging Azure services.

• https://azure.microsoft.com/en-us/services/load-balancer/
• https://docs.microsoft.com/en-us/azure/load-balancer/
• https://docs.microsoft.com/en-us/azure/load-balancer/quickstart-create-load-balancer-portal
• https://docs.microsoft.com/en-us/azure/load-balancer/tcp-and-udp-load-balancing

Published 01/14/2020

Load balancing refers to evenly distributing load (incoming network traffic) across a group of backend resources or servers.

Azure Load Balancer operates at layer four of the Open Systems Interconnection (OSI) model. It's the single point of contact for clients. Load Balancer distributes inbound flows that arrive at the load balancer's front end to backend pool instances. These flows are according to configured load balancing rules and health probes. The backend pool instances can be Azure Virtual Machines or instances in a virtual machine scale set.

A public load balancer can provide outbound connections for virtual machines (VMs) inside your virtual network. These connections are accomplished by translating their private IP addresses to public IP addresses. Public Load Balancers are used to load balance internet traffic to your VMs.

An internal (or private) load balancer is used where private IPs are needed at the frontend only. Internal load balancers are used to load balance traffic inside a virtual network. A load balancer frontend can be accessed from an on-premises network in a hybrid scenario.

Figure depicts both public and internal load balancers directing traffic to port 80 on multiple servers on a Web tier and port 443 on multiple servers on a business tier.

Figure: Balancing multi-tier applications by using both public and internal Load Balancer

For more information on the individual load balancer components, see Azure Load Balancer components.

Why use Azure Load Balancer? With Standard Load Balancer, you can scale your applications and create highly available services. Load balancer supports both inbound and outbound scenarios. Load balancer provides low latency and high throughput, and scales up to millions of flows for all TCP and UDP applications.

Key scenarios that you can accomplish using Standard Load Balancer include:

Load balance internal and external traffic to Azure virtual machines.

Increase availability by distributing resources within and across zones.

Configure outbound connectivity for Azure virtual machines.

Use health probes to monitor load-balanced resources.

Employ port forwarding to access virtual machines in a virtual network by public IP address and port.

Enable support for load-balancing of IPv6.

Standard Load Balancer provides multi-dimensional metrics through Azure Monitor. These metrics can be filtered, grouped, and broken out for a given dimension. They provide current and historic insights into performance and health of your service. Resource Health is also supported. Review Standard Load Balancer Diagnostics for more details.

Load balance services on multiple ports, multiple IP addresses, or both.

Move internal and external load balancer resources across Azure regions.

Load balance TCP and UDP flow on all ports simultaneously using HA ports.

Secure by default Standard Load Balancer is built on the zero trust network security model at its core. Standard Load Balancer secure by default and is part of your virtual network. The virtual network is a private and isolated network. This means Standard Load Balancers and Standard Public IP addresses are closed to inbound flows unless opened by Network Security Groups. NSGs are used to explicitly permit allowed traffic. If you do not have an NSG on a subnet or NIC of your virtual machine resource, traffic is not allowed to reach this resource. To learn more about NSGs and how to apply them for your scenario, see Network Security Groups. Basic Load Balancer is open to the internet by default. In addition, Load Balancer does not store customer data.

Fair Use Source: https://docs.microsoft.com/en-us/azure/load-balancer/load-balancer-overview