What is the back end?

The back-end can feel very abstract, but it becomes clearer when we explain it in terms of the front-end! To oversimplify a bit, the front-end is the parts of a webpage that a visitor can interact with and see.

Various tools and frameworks can be used to make a webpage, but, at its core, the front-end is composed of JavaScript, CSS, HTML, and other static assets, such as images or videos. Static assets are files that don’t change. When a visitor navigates to a webpage, these assets are sent to their browser.

Visiting a simple website is like ordering delivery from a restaurant: we place an order for our meal, and, once it’s delivered to us, we have it entirely in our possession. In this analogy, we can think of the front-end as everything that’s dropped off with the delivery: the containers, the utensils, and the food itself.

You’ll sometimes hear front-end development referred to as client-side development. Our instinct might be to think of the client as the human visitor or user of a website, but when referring to the client in web development, we’re usually referring to the non-human requester of content. In the case of visiting a website, the client is the browser, but in other circumstances, a client might be another application, a mobile device, or even a “smart” appliance!

While the front-end is the part of the website that makes it to the browser, the back-end consists of all the behind-the-scenes processes and data that make a website function and send resources to clients.

We talked about how the front-end consists of the information sent to a client so that a user can see and interact with a website, but where does the information come from? The answer is a web server.

The word “server” can mean a lot of things in computing, but we’re going to focus on web servers specifically. A web server is a process running on a computer that listens for incoming requests for information over the internet and sends back responses. Each time a user navigates to a website on their browser, the browser makes a request to the web server of that website. Every website has at least one web server. A large company like Facebook has thousands of powerful computers running web servers in facilities located all around the world which are listening for requests, but we could also run a simple web server from our own computer!

The specific format of a request (and the resulting response) is called the protocol. You might be familiar with the protocol used to access websites: HTTP. When a visitor navigates to a website on their browser, similarly to how one places an order for takeout, they make an HTTP request for the resources that make up that site.

For the simplest websites, a client makes a single request. The web server receives that request and sends the client a response containing everything needed to view the website. This is called a static website. This doesn’t mean the website is not interactive. As with the individual static assets, a website is static because once those files are received, they don’t change or move. A static website might be a good choice for a simple personal website with a short bio and family photos. A user navigating Twitter, however, wants access to new content as it’s created, which a static website couldn’t provide.

A static website is like ordering takeout, but modern web applications are like dining in person at a sit-down restaurant. A restaurant patron might order drinks, different courses, make substitutions, or ask questions of the waiter. To accomplish this level of complexity, an equally complex back-end is required.

When a user navigates to google.com, their request specifies the URL but not the filename for today’s Google Doodle. The web application’s back-end will need to hold the logic for deciding which assets to send. Moreover, modern web applications often cater to the specific user rather than sending the same files to every visitor of a webpage. This is known as dynamic content.

The collection of programming logic required to deliver dynamic content to a client, manage security, process payments, and myriad other tasks is sometimes known as the “application” or application server. The application server can be responsible for anything from sending an email confirmation after a purchase to running the complicated algorithms a search engine uses to give us meaningful results.

The back-ends of modern web applications include some sort of database, often more than one. Databases are collections of information. There are many different databases, but we can divide them into two types: relational databases and non-relational databases (also known as NoSQL databases). Whereas relational databases store information in tables with columns and rows, non-relational databases might use other systems such as key-value pairs or a document storage model. SQL, Structured Query Language, is a programming language for accessing and changing data stored in relational databases. Popular relational databases include MySQL and PostgreSQL while popular NoSQL databases include MongoDB and Redis.

In addition to the database itself, the back-end needs a way to programmatically access, change, and analyze the data stored there.

In order to deliver the front-end of a website or web application to a user, a lot needs to happen behind the scenes on the back-end! Understanding what makes up the back-end can be overwhelming because the back-end has a lot of different parts, and different websites or web applications can have dramatically different back-ends.

• The front-end of a website or application consists of the HTML, CSS, JavaScript, and static assets sent to a client, like a web browser.
• A web server is a process running on a computer somewhere that listens for incoming requests for information over the internet and sends back responses.
• Storing, accessing, and manipulating data is a large part of a web application’s back-end
• Data is stored in databases which can be relational databases or NoSQL databases.
• The server-side of a web application, sometimes called the application server, handles important tasks such as authorization and authentication.
• The back-end of web application often has a web API which is a way of interacting with an application’s data through HTTP requests and responses.
• Together the technologies used to build the front-end and back-end of a web application are known as the stack, and many different languages and frameworks can be used to build a robust back-end.