Azure Application Gateway vs Azure Load Balancer vs Azure Traffic Manager vs Azure Front Door

Load balancing aims to optimize resource use, maximize throughput, minimize response time, and avoid overloading any single resource. It can also improve availability by sharing a workload across redundant computing resources.

Azure provides various load balancing services that you can use to distribute your workloads across multiple computing resources - Application Gateway, Load Balancer, Traffic Manager and Front Door.

1. Application Gateway:
   1. Azure Application Gateway is a web traffic load balancer that enables you to manage traffic to your web applications
   2. Application Gateway can make routing decisions based on additional attributes of an HTTP request, for example, URI path or host headers.
   3. We can use Application Gateway with Web Application Firewall (WAF) for a scalable and secure way to manage traffic to your web applications.
2. Load Balancer
   1. Azure Load Balancer operates at layer 4 of the Open Systems Interconnection (OSI) model.
   2. 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.
   3. The backend pool instances can be Azure Virtual Machines or instances in a virtual machine scale set.
   4. A public load balancer can provide outbound connections for virtual machines (VMs) inside your virtual network
   5. Public Load Balancers are used to load balance internet traffic to your VMs
   6. An internal (or private) load balancer is used where private IPs are needed at the frontend only.
   7. Internal load balancers are used to load balance traffic inside a virtual network.
3. Traffic Manager
   1. Azure Traffic Manager is a DNS-based traffic load balancer. This service allows you to distribute traffic to your public-facing applications across the global Azure regions. Traffic Manager also provides your public endpoints with high availability and quick responsiveness
4. Front Door
   1. Azure Front Door is a global, scalable entry-point that uses the Microsoft global edge network to create fast, secure, and widely scalable web applications.
   2. With Front Door, you can transform your global consumer and enterprise applications into robust, high-performing personalized modern applications with content that reach a global audience through Azure
   3. Front Door works at Layer 7 (HTTP/HTTPS layer) 

Below information will help you to choose service wisely:

• If you want to load balance between your servers in a region at the application layer, review Application Gateway.
• To do network layer load balancing, review Load Balancer.
• If you are looking to do DNS-based global routing and do not have requirements for Transport Layer Security (TLS) protocol termination ("SSL offload"), per-HTTP/HTTPS request or application-layer processing, review Traffic Manager.
• If you need to optimize the global routing of your web traffic and optimize top-tier end-user performance and reliability through quick global failover, see Front Door.

I hope this article will help you to understand the available 'Azure Load Balancing Service'.

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