Load balancing, as the name suggests, refers to the process of balancing the load among virtual machines and applications. With one virtual machine, there is no need of load balancer because the entire load is on a single virtual machine and there is no other virtual machine to share the load. However, with multiple virtual machines containing the same application and service, it is possible to distribute the load among them through load balancing. Azure provides a couple of resources for enabling load balancing:

• Load balancers: Azure load balancer helps in architecting solutions with high availability.  Within the TCP stack, it is a layer 4 transport level load balancer. It is a layer 4 load balancer that distributes incoming traffic among healthy instances of services defined in a load-balanced set. Level 4 load balancers work at transport level and have network level information such as IP address and port to decide the target for the incoming request. Load balances are discussed in detail later in this chapter.
• Application gateways: Azure application gateways deliver High Availability to your applications. It is a layer 7 load balancer that distributes the incoming traffic among healthy instances of services. Level 7 load balancers can work at the application level and has application level information such as cookies, HTTP, HTTPS, and sessions for the incoming request. Application gateways are discussed in detail later in this chapter.