Domain name system
In the diagrams
Hero diagram › ClientHero diagram › DNSDesign Mint.com › DNSDesign Pastebin.com (or Bit.ly) › DNSDesign a key-value cache to save the results of the most recent web server queries › DNSDesign Amazon's sales rank by category feature › DNSDesign a system that scales to millions of users on AWS › DNSDesign the data structures for a social network › DNSDesign the Twitter timeline and search › ClientDesign a web crawler › Client
Used in solutions
Original text
Domain name system
Source: DNS security presentation
A Domain Name System (DNS) translates a domain name such as www.example.com to an IP address.
DNS is hierarchical, with a few authoritative servers at the top level. Your router or ISP provides information about which DNS server(s) to contact when doing a lookup. Lower level DNS servers cache mappings, which could become stale due to DNS propagation delays. DNS results can also be cached by your browser or OS for a certain period of time, determined by the time to live (TTL).
- NS record (name server) - Specifies the DNS servers for your domain/subdomain.
- MX record (mail exchange) - Specifies the mail servers for accepting messages.
- A record (address) - Points a name to an IP address.
- CNAME (canonical) - Points a name to another name or
CNAME(example.com to www.example.com) or to anArecord.
Services such as CloudFlare and Route 53 provide managed DNS services. Some DNS services can route traffic through various methods:
- Weighted round robin
- Prevent traffic from going to servers under maintenance
- Balance between varying cluster sizes
- A/B testing
- Latency-based
- Geolocation-based
Disadvantage(s): DNS
- Accessing a DNS server introduces a slight delay, although mitigated by caching described above.
- DNS server management could be complex and is generally managed by governments, ISPs, and large companies.
- DNS services have recently come under DDoS attack, preventing users from accessing websites such as Twitter without knowing Twitter's IP address(es).