DNS: How the Internet Finds Everything (System Design for Beginners – Episode 8)

[0:00]So what happens when you type netflix.com in your browser? How does it get resolved? Now in one of the previous videos, we saw that the browser makes a request to something called as a DNS server, which gives us back the IP address for the Netflix server and that's how we're able to resolve it and call the Netflix server and then watch a video. But is it that simple? Not really, we'll actually break down the process right now. So in many cases what happens is your device will have a cache, which will have the IP address stored. So we don't even have to resolve with the help of the DNS server and we can just resolve with the help of our cash here and we can get the IP address and call the server. So what happens when you want to visit netflix.com for the first time, you'll hit the DNS server, but the DNS server is actually called as the recursive server or the resolver. And it doesn't have all the information required, so it doesn't have the IP address of the Netflix server. It actually has to make a lot of calls, as you can see here, to get the IP address of Netflix. Now, this is an eight-step process, the first step of the process is actually making the request to the DNS server. The second step is calling the root servers. The root servers are run by companies like Verisign, NASA, and the Department of Defense, and they have information about the TLD or the top-level domain. For example, in our case, we are hitting netflix.com, so we need information about the .com server or the authoritative .com server, which will have information about where Netflix is. But the .com authoritative server actually gives us the SLD information, which is the information for Netflix, which is the second level domain information. So this also only has the information of the server, the domain name server, which actually has the information of the IP address for Netflix. So I wanted to share something really interesting with you. A few months back, I started running an advanced system design cohort, which is specifically meant for people with industry experience, who want to break into engineering leadership positions. So if you want to be a director of engineering, VP of engineering, or want a CXO title, you'd want to know a lot more about system design from the application perspective. And just the basics of system design, DSA, and coding will not cut it. You'll need to understand systems from end-to-end, you'll need to become an expert at architecting systems, understanding how things scale, and how to plan better for bigger, much more scalable products. And this is what we break down in my three-month advanced system design cohort. There are 20 people already in the cohort, some of them even have 25 years of experience in the industry. So if you think you've hit the limit in your system design learning, and you want to take things to the next level and deeply connect with people who are just like you, people with great industry experience and exposure, wanting to move on to the leadership positions, you might want to check out my cohort. The link for the form is in the description of this video. Fill it up, we'll check if you're a good fit, and then we'll set up a call with you, and then we'll take things forward. Now let's get back to the video. Now, this information is sent back in step number eight to our browser, and the browser actually finally makes a request to Netflix server, because now we have the IP address. So we broke down what looks like a simple process of just calling the DNS resolver. That's actually an eight-step process, so there's a lot happening when you visit a website for the first time. So just a quick recap, the user types the website name into a web browser and the query travels into the Internet and is received by a DNS recursive resolver. The resolver then queries a DNS root name server. And the root server then responds to the resolver with the address of a Top Level Domain TLD DNS server, such as .com or .net, which stores the information for its domains. When searching for example.com, our request is pointed toward the .com TLD. The resolver then makes a request to the .com TLD. The TLD server then responds with the IP address of the domain's name server, example.com. And lastly, the recursive resolver sends a query to the domain's name server. The IP address for example.com is then returned to the resolver from the name server. And the DNS resolver then responds to the web browser with the IP address of the domain requested initially. Once the eight steps of the DNS lookup have returned the IP address for example.com, the browser is able to make the request for the web page, and the browser makes a HTTP request to the IP address of the server, and the server returns the web page to be rendered in the browser. So now that we understand this critical concept, we can go further and explore more about APIs and REST APIs.