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Struggling to tell your APIs from your CDNs? Read our comprehensive cloud computing glossary covering the most common terms.
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The Domain Name System (DNS) is sometimes referred to as the “phonebook of the internet.” Just like we no longer memorize phone numbers but use contact names instead, users can also access websites and resources in the same way using DNS with human-readable domain names (example.com) instead of numerical IP addresses. The DNS takes domain names and translates them into IP addresses, allowing devices to communicate with servers. Twitter or social media would be extremely towered to access without DNS. Users would have to memorize every string of numbers for every website they accessed.
When a user enters a URL in their browser to try and go to a website, a number of components of the DNS work together to resolve that domain to an IP address. The general process for DNS resolution follows these steps:
1. If the browser cache has any IP address information, it will find it there first in the browser cache.
2. If it does not find any IP address information for the domain there, the request goes to the operating system cache level second.
3. If the OS level does not resolve it, the request goes to the DNS resolver which is usually provided to the user through their ISP.
4. The DNS resolver requests and waits from a root DNS server it is pointing to, which points the resolver to a top-level domain (TLD) server. For example, if it’s a .com site, the resolver would ask the TLD server about the IP address of the “example.com” domain name.
5. The root server points to a “com” TLD server.
6. The resolver asks the TLD server for the authoritative name server for that domain.
7. The authoritative name server returns the information for the correct IP address to the DNS resolver.
The browser receives the IP address back from the DNS server and used the name given to connect to that web server.
A Record (Address Record): An A-record maps a domain name a IPv4 address.
AAAA Record: An AAAA record maps a domain with the IPv6 address.
CNAME Record (Canonical Name Record): CNAME records point a domain to a different domain or aliasing.
MX Record (Mail Exchange Record): The MX record lists which mail servers email to the domain will be sent through.
NS Record (Name Server Record): The NS record lists the authoritative name servers for the domain name.
TXT Record: TXT records are different from other types of records in that they can store arbitrary text. These record types are often used for verification and email security.
User Experience: DNS offers a consistent experience for the user. The domain name is easier to remember and therefore when we connect to the internet using web browser, it is more convenient. If we did not have DNS, accessing distinct sections of the internet would often be confusing and impractical.
Performance Optimization: In a world of large network delays, DNS caching at multiple levels (browser, system, resolver) significantly speeds up access to web pages users frequent (and maybe links in email they receive).
Security Layers: Modern DNS equipping itself with security options like DNSSEC (Domain Name System Security Extensions) and some protocols to avoid DNS Spoofing and/or man in the middle attacks.
Business Continuity: If configured correctly, DNS tries to offer redundancy and high-availability for business’ web sites and services.
Take a massive ecommerce company like Amazon. When users type www.amazon.com, the DNS queries that domain and returns an IP address that maps to the servers hosting Amazon’s website. Because Amazon has global traffic, they have multiple DNS records pointing to different server locations. This allows Amazon to serve content to its customers quickly because they can reroute customers to alternate server locations if one server fails and is unable to serve a given page.
Additionally, Amazon’s use of DNS goes beyond just their website. Amazon also utilizes DNS resolution for their various email systems (by leveraging MX records) as well as for their content delivery networks (CDNs), as well as disposing of their purchased domains from 3rd party registrars who package these capabilities into their sentinel offerings for customer authentication.
