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Okay, so before we talk about Route 53,

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we have to talk about what is a DNS.

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So this is a basic level lecture,

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but at least it will help you understand how DNS works.

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And this is something you've been using

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behind the scenes everyday, but you don't know

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about it exactly.

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So let's have a look.

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So a DNS is a domain name system,

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and what it will do is that it will translate

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human friendly hostnames into the target

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server IP addresses.

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For example, when you type in your web browser,

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wwww.google.com, it will in the end, give you back

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an IP address, and this is the IP address

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that your web browser will be able to access

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behind the scenes and get some data back from Google.

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So the DNS is the backbone of the internet,

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it is a way for you to understand how to translate

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these URLs, these hostnames into IPs.

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So there is a hierarchical naming structure for DNS,

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and the idea is that at the root of www.google.com,

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for example, there is the .com,

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but then there is example.com, which has a bit more precise,

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then www.example.com or api.example.com.

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So all of these are going to be the hierarchy

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of your domain names.

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Next, we need to define a little bit

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of terminology regarding your DNS.

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So there is a domain registrar, this is where you're going

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to register your domain names,

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and it could be Amazon Route 53, or it could be GoDaddy

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or any other domain registrar you can find online.

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Then you have DNS records and there are different types,

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and we'll have a look at them in detail in this section.

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So it could be A, quadruple A, CNAME, NS,

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et cetera, et cetera.

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Don't worry, we'll see those in detail in this section.

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The Zone File, which contains all the DNS records.

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So this is how to match these host names to IPs

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or addresses.

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Name Servers is servers that will actually resolve

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the DNS queries.

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And we'll have a look at them as well in the section.

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Top Level Domains, which is .com, .us, .in,

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.gov, .org, et cetera, et cetera.

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Second Level Domain, which is amazon.com, google.com.

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So you can see there are two words in between dots.

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And so if we take a look for example,

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at this FQDN, so Fully Qualified Domain Name,

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we have http://api.www.example.com.

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Okay, so the last dor at the end is called the root

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and is the root of all the domain names.

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Then the .com, so .com is your TLD.

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So that's your Top Level Domain.

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The example.com is going to be your second level domain.

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Then we have www.example.com that's your sub-domain,

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then api.www.example.com is your domain name, okay?

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The HTTP part of it is the protocol you want to use.

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And altogether we have the FQDN,

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which is the Fully Qualified Domain Name.

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So now that we know a little bit of terminology,

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let's have a look at how DNS works.

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So we have a web server, and let's say for example,

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that we have an IP, it's a public IP,

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could be an easy two instance, for example,

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and the public IP is 9.10.11.12,

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and we want to be able to access this using

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the example.com domain name.

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So we're going to register this example.com domain name

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on one our servers for the DNS.

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But let's see how the computer, your web browser

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can access it and can get that response.

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So your web browser is going to want to access example.com

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and to do so, it's going to ask its local DNS server.

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"Hey, do you know what example.com is?"

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Now this local DNS server is usually assigned

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and managed by your company or assigned

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by your internet service provider, dynamically.

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And if the local DNS server has never seen

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this query before, what it's going to do is first

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ask the root DNS server managed by the ICANN,

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the ICANN organization, and is going to say,

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"Hey, do you know what's example.com?"

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Which is the first server that's going to be asked.

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And the root DNS server is going to say,

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"I've never seen it, but I know .com."

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So .com is NS so it's an NS record, Named Server

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and go see 1, 2, 3, 4, this public IP.

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So this is saying to local DNS,

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"Hey, I don't have this answer,

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but I'm getting you a little bit closer to your answer

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because I know the .com domain and the .com domain

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name server has this IP 1, 2, 3, 4."

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So the local DNS servicing.

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Okay, good, now I'm going to ask the top level domain.

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So the .com domain server at 1, 2, 3, 4,

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I'm going to ask for the answer of my query.

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So this is another domain managed by IANA, the IANA

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and the example.com, is going to be asked again

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to this DNS server.

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So do you know about example.com?

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And the DNS server is going to say,

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"Hey, I don't know about example,

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I do know about example.com."

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"I don't know the answer to your query right away,

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I don't know which record it is,

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but there is a server called example.com that I know about,

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which is at 5.6.7.8."

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"That's a public IP that you should ask the answer

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to your question."

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So the local DNS server is then going to go

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to our final server, which is the sub-level domain

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DNS server, and this is a server that is going to be managed

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by your domain registrar.

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So it could be for example, Amazon Route 53 and so on.

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So the DNS server's gonna say,

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"Hey, do you know about example.com?"

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And the DNS server will have an entry,

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for example.com, and so it will say,

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"Hey, yes, of course, I know example.com,

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and it turns out that example.com, I know that it's

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an A record and that's the result of it

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is the IP 9.10.11.12."

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So the DNS server now knows the answer

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by recursively asking DNS servers

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and finding the most specific one.

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And then it says, "Okay, hey, yes,

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I'm going to cash that answer right away,

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because I want to be able to, if someone is asking me again,

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for example.com I want to right away give them the answer."

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So it's going to send back the answer into your web browser

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and your browser now has the answer.

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And using this IP address then is going to be able

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to access your web server.

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So this is how DNS works, so you've been using DNS

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behind the scenes, all along, all your life.

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For example, when you access www.google.com,

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you're using DNS or any websites,

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but now we see how the DNS queries work.

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So this is just some background knowledge,

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because now we're going to go into Route 53 and learn

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how to manage a DNS server on our own.

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So hope you liked it,

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and I will see you in the next lecture.