AWS Load Balancer

Why do we need AWS Load Balancer?

To set up a web application, you would need a server. There is a limitation on the number of requests a server can accept. If your web application suddenly receives a high number of requests, your server goes down. As a solution to this problem, you will set up more servers. However, when the requests are less, you are wasting the resource since you would have not required so many servers.
To solve the above problem, AWS came up with a solution - AWS Auto Scaling. AWS Autoscaling will auto upscale and downscale the servers based on the traffic and server performance. We can configure Auto Scaling to create a new EC2 when the resource reaches a certain threshold: maybe 80% CPU or 70% memory. This is just an example.

This was all about Auto Scaling. Next, how do we know how many requests a server can handle? In other words, if I have configured Auto-Scaling and there are three servers running; each server can handle 100 requests. Now, there are 90 requests, and all 90 requests are handled by the first server. This is not the right way of balancing the requests. Hence, AWS provided a Load Balancers service.

Using Load balancers service, we can route the request based on certain criteria. Something like this: www.myblog.com requests are routed to a default server. www.myblog.com/India will route another server. Similarly, www.myblog.com/Canada will route to another server.

There are three types of Load Balancers -

a. Classic Load Balancer

    The requests are routed to each server in a round-robin way, and it will not check the request headers.

b. Application Load Balancer

    The ALB works in the Application Layer (Layer 7) of the OSI model. It distributes the requests based on a certain condition. I can deploy different application for different locales on different servers. Requests for each server could get routed to different servers based on the locale in the path; Something like this: www.myblog.com requests are routed to a default server. www.myblog.com/India will route another server. Similarly, www.myblog.com/Canada will route to another server. Similarly, we can different conditions.

c. Network Load Balancer

    A Network Load Balancer makes routing decisions at the transport layer (TCP/SSL). It has the highest performance, and when there is a sudden spike in the traffic, it handles pretty well. This is where NLB shines.