The story of a web application 

Before we tackle the different use cases and the building blocks in the rest of the chapter, let's refresh the concepts of how a standard three-tier application would work. If you are wondering as to why this is important, it's because it provides an understanding of the building blocks that we will deal with in the latter part of the chapter. 

Most applications found today are web applications (applications accessible through a web browser). These range from relatively simple websites such as WordPress, to complicated systems such as Wolfram Alpha. These applications were traditionally 3-tier, comprising of a web-tier, an application-tier, and finally the database-tier. 

Now, let's take a look at an enterprise application, such as an employee management system. There are several products on the market, but essentially, it's a system where one would log in to apply for leave, check payslips, and so on. More often than not, this is a web-based system, be it PeopleSoft, an SAP HR module, or a new age SaaS platform such as Workday. 

I have chosen the application on purpose, as most of us probably use one at work, it's normally deployed as an internal application (except Workday of course, that's a SaaS), and has role-based access. 

Now, you go to a URL that has been provided to you, you sign in, typically using your enterprise credentials, the system logs you in, and shows us the options that we are entitled to. 

Behind this simple task of pulling up the website, there are several steps that happen. We will take a look at two aspects of it: 

• Transport level 
• Application level