07 - Route 53

What is DNS?

awsdnsnetworkingroute53saa-c03

Overview

Before diving into Amazon Route 53, we need to understand DNS (Domain Name System) — the backbone of the internet. DNS is something you've been using behind the scenes every single day, but you may not know exactly how it works.

DNS translates human-friendly hostnames (like www.google.com) into machine-readable IP addresses (like 172.217.18.36). Without DNS, you'd have to memorize IP addresses for every website you visit. DNS is what makes the internet usable for humans.

Why This Matters for the Exam

Understanding DNS fundamentals is essential for Route 53 questions. The exam tests your knowledge of record types, TTL behavior, and how DNS resolution works. This lecture provides the foundation for everything that follows.

DNS Hierarchy

DNS uses a hierarchical naming structure. Every domain name is built from right to left, from the most general to the most specific:

                    ┌─────────────────────────────────────────┐
                    │         DNS Hierarchy                    │
                    │                                         │
                    │              . (Root)                   │
                    │               │                         │
                    │         ┌─────┴─────┐                  │
                    │        .com        .org                 │
                    │         │                               │
                    │    example.com                          │
                    │         │                               │
                    │   www.example.com                       │
                    │         │                               │
                    │   api.www.example.com                   │
                    └─────────────────────────────────────────┘

DNS hierarchy

. (Root)managed by ICANN .com .org example.comSLD www.example.comsubdomain api.www.example.com.FQDN with root dot Names are built right to left, from the most general to the most specific.
A name is read right to left: root, TLD, SLD, then subdomains. The full name with the root dot is the FQDN.

DNS Terminology

Understanding these terms is critical for Route 53:

Term Definition Example
Domain Registrar Where you register/buy domain names Amazon Route 53, GoDaddy
DNS Records Entries that map hostnames to IPs/other hostnames A, AAAA, CNAME, NS
Zone File Contains all DNS records for a domain The file that maps hostnames to addresses
Name Server Server that resolves DNS queries Route 53's name servers
Top Level Domain (TLD) The last part of a domain .com, .org, .gov, .us, .in
Second Level Domain (SLD) The domain name itself amazon.com, google.com
FQDN Fully Qualified Domain Name — the complete address api.www.example.com.
Subdomain A domain under the SLD www.example.com, api.example.com

Anatomy of a URL

http://api.www.example.com.
│       │   │      │     │ │
│       │   │      │     │ └── Root (the final dot, usually hidden)
│       │   │      │     └──── TLD (Top Level Domain)
│       │   │      └────────── SLD (Second Level Domain)
│       │   └───────────────── Subdomain
│       └───────────────────── FQDN (Fully Qualified Domain Name)
└───────────────────────────── Protocol
The Hidden Root Dot

Every domain name technically ends with a dot (.) representing the root of the DNS hierarchy. When you type www.google.com in your browser, it's actually www.google.com. — the browser just hides the trailing dot. This root is managed by ICANN (Internet Corporation for Assigned Names and Numbers).

How DNS Resolution Works

When you type example.com in your browser, here's what happens behind the scenes — a recursive DNS resolution process:

┌──────────┐                                                              ┌──────────┐
│  Your    │                                                              │   Web    │
│  Browser │                                                              │  Server  │
│          │                                                              │ 9.10.11.12│
└────┬─────┘                                                              └──────────┘
     │                                                                         ▲
     │ 1. "What is example.com?"                                               │
     ▼                                                                         │
┌──────────────┐                                                               │
│  Local DNS   │  (Assigned by your ISP or company)                           │
│  Server      │                                                               │
│  (Resolver)  │                                                               │
└──┬───┬───┬───┘                                                               │
   │   │   │                                                                   │
   │   │   │  2. "Do you know example.com?"                                   │
   │   │   ▼                                                                   │
   │   │  ┌──────────────┐                                                    │
   │   │  │  Root DNS    │  Managed by ICANN                                  │
   │   │  │  Server      │  "I don't know, but .com is at 1.2.3.4"           │
   │   │  └──────────────┘                                                    │
   │   │                                                                       │
   │   │  3. "Do you know example.com?"                                       │
   │   ▼                                                                       │
   │  ┌──────────────┐                                                        │
   │  │  TLD DNS     │  Managed by IANA                                       │
   │  │  Server      │  "I know .com! example.com NS is at 5.6.7.8"          │
   │  │  (.com)      │                                                        │
   │  └──────────────┘                                                        │
   │                                                                           │
   │  4. "Do you know example.com?"                                           │
   ▼                                                                           │
  ┌──────────────┐                                                            │
  │  SLD DNS     │  Managed by YOUR domain registrar (e.g., Route 53)        │
  │  Server      │  "Yes! example.com A record = 9.10.11.12"                 │
  │ (example.com)│                                                            │
  └──────────────┘                                                            │
                                                                               │
   5. Local DNS caches the answer (for TTL duration)                          │
   6. Returns IP 9.10.11.12 to your browser                                  │
   7. Browser connects to 9.10.11.12 ─────────────────────────────────────────┘

Step-by-Step Breakdown

  1. Your browser asks the Local DNS Server (assigned by your ISP or company): "What is example.com?"
  2. The Local DNS Server doesn't know, so it asks the Root DNS Server (managed by ICANN). The Root says: "I don't know example.com, but I know .com — its name server is at 1.2.3.4."
  3. The Local DNS Server asks the TLD DNS Server (.com, managed by IANA): "What about example.com?" The TLD says: "I know about example.com — its name server is at 5.6.7.8."
  4. The Local DNS Server asks the SLD DNS Server (managed by your domain registrar, e.g., Route 53): "What is example.com?" The SLD says: "Yes! example.com is an A record pointing to 9.10.11.12."
  5. The Local DNS Server caches the answer for the duration of the TTL (Time To Live).
  6. The Local DNS Server returns the IP 9.10.11.12 to your browser.
  7. Your browser connects directly to 9.10.11.12 and loads the website.
Key Insight

DNS does not route traffic. It only resolves names to addresses. The actual HTTP traffic goes directly from your browser to the web server — it never passes through the DNS servers. This is a critical distinction that the exam tests.

Recursive DNS resolution

Browserexample.com? Local DNS serverresolver 1 Root DNS (ICANN)I know .com is at 1.2.3.4 TLD DNS .com (IANA)example.com NS is at 5.6.7.8 SLD DNS example.comA record = 9.10.11.12 2 3 4 5. cache for TTL 6. return the IP Web server9.10.11.12 7. The browser connects straight to the web server. DNS never carries the traffic.
The local DNS server asks Root, TLD and SLD servers in turn, caches the answer for the TTL and returns the IP. The browser then talks to the web server directly.

Caching and TTL

After the Local DNS Server resolves a query, it caches the result for the duration of the TTL. This means:

  • Subsequent requests for the same domain are answered instantly from cache
  • No additional DNS queries are needed until the TTL expires
  • This reduces load on DNS servers and speeds up browsing

We'll explore TTL in detail in Records and TTL.

Why This Matters for Route 53

Route 53 acts as the SLD DNS Server in the diagram above. When you register a domain with Route 53 (or point your domain's NS records to Route 53), it becomes the authoritative DNS for your domain. This means:

  • Route 53 is the source of truth for your DNS records
  • When someone queries your domain, Route 53 provides the answer
  • You have full control over what answers Route 53 gives

This is the foundation for everything we'll learn in this section — from simple A records to complex routing policies.

Questions & Answers

Q1: What is DNS and what does it do?

Answer:

DNS (Domain Name System) translates human-friendly hostnames (like www.google.com) into IP addresses (like 172.217.18.36) that computers use to communicate. It's the backbone of the internet — without DNS, you'd need to memorize IP addresses for every website.

Q2: What is the difference between a TLD and an SLD?

Answer:

  • TLD (Top Level Domain): The last part of a domain name — .com, .org, .gov, .us
  • SLD (Second Level Domain): The domain name itself — amazon.com, google.com The TLD is managed by IANA, while the SLD is managed by your domain registrar (like Route 53 or GoDaddy).
Q3: What is an FQDN?

Answer:

FQDN stands for Fully Qualified Domain Name. It's the complete domain name that specifies the exact location in the DNS hierarchy. For example, api.www.example.com. is an FQDN. It includes the subdomain, SLD, TLD, and the root dot (usually hidden by browsers).

Q4: What is a domain registrar?

Answer:

A domain registrar is a service where you register (buy) domain names. Examples include Amazon Route 53, GoDaddy, and Google Domains. The registrar manages the registration and ensures your domain is unique. Note: a domain registrar is different from a DNS service, though most registrars provide both.

Q5: How does recursive DNS resolution work?

Answer:

When you query a domain, the Local DNS Server recursively asks:

  1. Root DNS Server → "I know .com is at this NS"
  2. TLD DNS Server (.com) → "I know example.com is at this NS"
  3. SLD DNS Server (example.com) → "Here's the A record: 9.10.11.12" The Local DNS Server caches the result for the TTL duration and returns it to your browser.
Q6: What is the role of the Local DNS Server?

Answer:

The Local DNS Server (also called a resolver) is assigned by your ISP or company. It's the first server your browser contacts for DNS resolution. It performs the recursive lookup by querying Root → TLD → SLD servers, then caches the result so future queries for the same domain are answered instantly.

Q7: What are NS records?

Answer:

NS (Name Server) records specify which DNS servers are authoritative for a domain. They tell the DNS system "to find records for this domain, ask these name servers." When you register a domain with Route 53, it creates NS records pointing to Route 53's name servers.

Q8: Does DNS route traffic?

Answer:

No. DNS only resolves names to addresses. The actual HTTP/HTTPS traffic goes directly from your browser to the web server — it never passes through DNS servers. DNS just tells your browser which IP address to connect to. This is a critical distinction tested on the exam.

Q9: What is the root of the DNS hierarchy?

Answer:

The root is represented by a dot (.) at the end of every domain name (usually hidden by browsers). It's managed by ICANN. The root DNS servers know the addresses of all TLD servers (.com, .org, .gov, etc.) and are the starting point for every DNS resolution.

Q10: What organizations manage the different levels of DNS?

Answer:

  • Root DNS: Managed by ICANN (Internet Corporation for Assigned Names and Numbers)
  • TLD DNS (.com, .org): Managed by IANA (Internet Assigned Numbers Authority)
  • SLD DNS (example.com): Managed by your domain registrar (Route 53, GoDaddy, etc.) Each level delegates to the next, creating the hierarchical resolution chain.

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