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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 every day

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‫but you don't know 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, and what it will do

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‫is that it will translate human friendly hostnames

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‫into the target server IP addresses.

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‫For example, when you type in your web browser,

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‫www.google.com, it will in the end

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‫give you back an IP address and this is 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

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‫how to translate 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

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‫of www.google.com for example, there is the .com,

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‫but then there is example.com which is 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.

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‫This is where you're going 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 they have 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, AAAA, CNAME, NS, et cetera, et cetera.

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

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‫A zone file which contains all the DNS records.

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‫So, this is how to match these hostnames

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‫to IPs or addresses.

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‫Name servers is servers

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‫that will actually resolve the DNS queries.

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

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‫Top level domains which is .com, .us, .in, .gov, .org,

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‫et cetera, et cetera.

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‫Second level domain which is amazon.com and google.com.

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‫So you can see there are two words in between a dot.

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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?

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‫So, the last dot the end is called the root

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‫and it is the root of all the domain names.

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‫Then the .com,

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‫so .com is your TLD, 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.

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‫That's your subdomain.

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‫api.www.example.com is your FQDN,

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‫your fully qualified domain name.

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‫HTTP is going to be your protocol

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‫and all these things together is going to be your URL.

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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 EC2 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

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‫using 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 of 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 this query before

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‫what it's going to do is first ask the root DNS server

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‫managed by the I-C-A-N-N, the ICANN organization

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‫and is going to say, "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 Name server

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‫and go see 1234 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,

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‫and the .com domain name server has this IP, 1234."

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‫So the local DNS server saying, "Okay, good.

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‫Now I'm going to ask the top level domain."

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‫So the .com domain server at 1234.

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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 I-A-N-A, the IANA

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‫and the example.com, okay, 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 gonna say,

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‫"Hey, I do know about example.com.

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‫I don't have 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, that's a public IP

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‫that you should ask the answer to your question.

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‫So, local DNS server is then going go to our final server

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‫which is the sub-level domain DNS server

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‫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 is 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 for example.com.

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‫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,

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‫I know that it's an A record

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‫and that the result of it 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 cache that answer right away

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‫because I want to be able to,

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‫if someone is asking me again for example.com

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‫I want to get it right away, give them the answer."

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

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‫and your web browser now has the answer

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‫and using this IP address

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‫then is going to be able to access your web server.

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‫So, this is how DNS works.

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‫So, you've been using DNS behind the scenes

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‫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 website.

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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

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‫and learn how to manage a DNS server on our own.

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‫So I hope you liked it

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‫and I will see you in the next lecture.