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A comprehensive Guide to Azure Load Balancer
Updated on 25th Feb, 23 401 Views

The number of users employing the various resources that Azure provides is increasing enormously. And the applications and services that rely on these resources are also becoming more complex and are required to be able to handle requests coming in from a global level.

Azure provides load balancing features that enable the efficient use of its resources. This blog will give a comprehensive idea about load balancing in Azure through the following topics:

What is Load Balancing?

The logical and efficient distribution of network or application traffic among numerous servers in a server farm is known as load balancing. Each load balancer lies between client devices and backend servers, accepting and then efficiently distributing incoming requests to a server that can handle them.

A load balancer distributes traffic to several web servers in the resource pool, regardless of whether it’s hardware or software, or what algorithm(s) it employs. This ensures that no single server becomes overloaded and hence, unreliable. Load balancers are useful for reducing server response time and increasing throughput.

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Types of Load Balancers

A load balancer might take the form of a physical device, a virtualized instance running on specialized hardware, or a software process. As concurrent demand for software-as-a-service (SaaS) applications grows, providing them to end-users consistently can become difficult if effective load balancing isn’t in place.

Server resources must be easily available and load-balanced at Layers 4 and/or 7 of the Open Systems Interconnection (OSI) model to promote higher consistency and keep up with ever-changing user demand:

  • Load balancers in Layer 4 (L4) operate at the transport level. That means they may route packets depending on their source and destination IP addresses, as well as the TCP or UDP ports they employ. Network Address Translation is performed by L4 load balancers, although they do not verify the contents of each packet.
  • Load balancers at Layer 7 (L7) act at the application level, which is the highest in the OSI model. When selecting how to distribute requests over the server farm, they can consider a wider range of data than their L4 counterparts, such as HTTP headers and SSL session IDs.

In addition to conventional L4 and L7 load balancing, global server load balancing (GSLB) can expand either type’s capabilities over several data centers, allowing massive volumes of traffic to be efficiently distributed while ensuring that the end-user experience is not harmed.

What is Azure Load Balancer?

Microsoft Azure is Microsoft’s public cloud computing platform that provides a variety of cloud services such as analytics, computation, networking, and storage. To operate existing applications or build and expand new apps on the public cloud, the customer can pick and choose from various services.

Load Balancing in Azure is a cloud-based system that accepts client requests, determines which machines in the set can handle them, and then forwards those requests to the appropriate machines.

Types of Load Balancers in Azure

Outbound connections for virtual machines (VMs) within your virtual network can be provided via a public load balancer. These connections are made possible by converting private IP addresses to public IP addresses.

Load balancing is done using public load balancers to distribute internet traffic to your virtual machines.

When only private IPs are required at the frontend, an internal (or private) load balancer is employed. Inside a virtual network, internal load balancers are employed to balance traffic. In a hybrid setup, a load balancer frontend can be accessible from an on-premises network.

Load Balancing Services in Azure

Azure provides many load balancing services of which the users can select the one that matches their workload’s requirement. They are:

Azure Traffic Manager

Azure Traffic Manager is a load balancer for DNS traffic. Using DNS-based traffic routing mechanisms, it can distribute traffic to services across global Azure regions as efficiently as possible. It can prioritize user access, assist in data sovereignty compliance, and alter traffic to accommodate app upgrades and maintenance.

Azure Traffic Manager supports:

  • Layer 7
  • Apps that are available worldwide

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Azure Load Balancer

Azure Load Balancer is a network-layer load balancer from Microsoft. Its low-latency, layer 4 load balancing features help you build high availability and network performance into your applications. It can balance traffic between Azure Virtual Machines (VMs) and multitiered hybrid apps within your virtual networks.

Azure Load Balancer supports:

  • TCP and UDP
  • Layer 4
  • Apps that are both global and regional

The Open Systems Interconnection (OSI) model’s layer 4 is where Azure Load Balancer functions. It is the client’s single point of contact. Inbound flows that arrive at the load balancer’s front end are distributed to backend pool instances by the Azure load balancer.

These flows are based on load-balancing rules and health probes that have been set up. Azure Virtual Machines or instances from a virtual machine scale set can be used as backend pool instances.

Load balancing rules: Load balancing rules specify how traffic should be routed once it arrives at the load balancer. These rules can be used to send traffic to a backend pool. Client IPs can be directed to the same backend virtual machines if session persistence is enabled.

Health probes: When the health probe in the backend pool detects any failed virtual machines in a load balancer, it stops routing traffic to that particular failed virtual machine. It can set up a health probe to check the health of the backend pool’s instances.

Azure Application Gateway

As a service, Azure Application Gateway provides an application delivery controller. Using layer 7 load balancing capabilities, it can turn web front ends into scalable and highly available programs and securely distribute regional applications.

Azure Application Gateway supports:

  • HTTP, HTTPS, and HTTP/2
  • Layer 7
  • Apps for a certain region
  • Firewall for web applications
  • Offloading SSL/TLS

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Azure Front Door

Azure Front Door supports the delivery of highly secure worldwide applications. Using the Microsoft global edge network, it can deliver the real-time performance of global online applications. It can transform many microservice apps into a single, more secure app delivery architecture by accelerating content.

Azure Front Door supports:

  • HTTP, HTTPS, and HTTP/2
  • Layer 7
  • Apps that are available worldwide
  • Firewall for web applications
  • Offloading SSL/TLS

Azure Load Balancer Pricing

Load Balancing is available in Basic and Standard tiers. The Basic tier is free of charge and the pricing in the Standard tier for Azure load balancer is:

Standard Load BalancerPrice
First 5 rules₹1.802/hour
Additional rules₹0.721/rule/hour
Inbound NAT rulesFree
Data processed₹0.361 per GB

Prices differ for different regions. These prices are for the Central India region.

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Features of Azure Load Balancer

The Load Balancer features are:

  • Azure load balancing employs a 5-tuple hash that includes the source IP, source port, destination IP, destination port, and protocol.
  • When the load balancer scales up or down instances based on conditions, it can reconfigure itself. As a result, if more virtual machines are added to the backend pool, the load balancer will automatically reconfigure.
  • All outbound flows from our virtual network’s private IP addresses to public IP addresses on the Internet can be translated to the load balancer’s frontend IP.
  • When the health probe in the backend pool detects any failed virtual machines in a load balancer, it stops routing traffic to that particular failed virtual machine. It can set up a health probe to check the health of the backend pool’s instances.
  • It does not communicate directly with TCP or UDP protocols. Traffic can be routed based on URL or multi-site hosting.
  • If we have a pool of web servers and don’t want to provide each one a public IP address, we can use the load balancer’s port forwarding feature.

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Creating Azure Load Balancer

The step-by-step process of creating an Azure Load Balancer is as follows:

  1. Log in to the Azure Portal and search for the load balancer.

  1. Click on Create and Enter the details.

  1. After entering the following details click on Review + create.
    Subscription: Select your subscription.
    Resource group: Select an existing resource group or create a new one
    Name: Enter a name for your Load Balancer
    Region: Select location
    Type: Select Public
    SKU: Select Basic
    Public IP address: Select Create New. If you have an existing Public IP you would like to use, select Use existing.
    Public IP address name: Type myPublicIP in the text box.

  1. Now click on Create after reviewing your details.

  1. After deployment is complete, click on Go to resource to open the created load balancer resource.

Creating a Health Probe

  1. After opening the resource, to create a health probe click on Health probes from the left-hand menu and then on the Add button.

  1. Enter the required details and click on Add.

Create a Load Balancer Rule

  1. In the Load Balancer, resource page click on Load balancing rules from the left-hand menu and then on the Add button.

  1. Use the required configurations and click on Add.

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Why Azure Load Balancer?

You can scale your apps and establish highly available services with Azure Load Balancer. Both incoming and outbound situations are supported by the Load Balancer. For both TCP and UDP applications, the Load Balancer provides low latency and high throughput, and scalability up to millions of flows.

The following are some of the scenarios that Azure Standard Load Balancer can help you with:

  • Internal and external traffic to Azure virtual machines should be load balanced.
  • Distribute resources inside and across zones to increase availability.
  • Configure Azure virtual machines’ outbound connectivity.
  • Monitor load-balanced resources with health probes.
  • To reach virtual computers in a virtual network using a public IP address and port, use port forwarding.
  • Allow IPv6 load balancing to be enabled.
  • Through Azure Monitor, a standard load balancer may give multidimensional information. For each dimension, these metrics can be filtered, grouped, and broken apart.

They provide real-time and historical data about your service’s performance and health. For these metrics, Insights for Azure Load Balancer provides a predefined dashboard with useful visuals. The concept of resource health is also supported. For further information, see Standard load balancer diagnostics.

  • Load balancing services on multiple ports, IP addresses, or both are available.
  • Move load balancer resources between Azure regions, both internal and external.
  • Using HA ports, load-balance TCP and UDP flow on all ports at the same time.

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Limitations of Azure Load Balancer

A load balancer is a UDP or TCP product that performs port forwarding and load balancing for IP protocols. For UDP and TCP, inbound NAT rules and load balancing rules are supported.

However, other IP protocols, such as ICMP, are not. The load balancer is not a proxy and does not interact, respond, or terminate with the payload of a TCP or UDP flow.

Azure internal load balancers do not translate outbound originated connections to the internal load balancer frontend because both are in the private IP address space, unlike public load balancers that offer outbound connections when transitioning to public IP addresses from private IP addresses inside the virtual network.

This eliminates the potential of SNAT port exhaustion in the isolated internal IP address space when the translation isn’t necessary.


Users that need multi-tier applications with worldwide accessibility and scalability can use load-balancing algorithms to send clients to the closest endpoint. The Azure load balancer distributes networking traffic burden to backend virtual machines, and its scaling functionality is extremely useful during both high and low loads. The main advantage of creating your own load-balancing rules is flexibility.

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