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A Domain Name System (DNS) translates a domain name such as www.example.com to an IP address. DNS Architecture

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How DNS Works

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).

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DNS Record Types

  • 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 an A record.

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Managed DNS Services

Services such as CloudFlare and Route 53 provide managed DNS services. Some DNS services can route traffic through various methods:

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Weighted Round Robin

  • Prevent traffic from going to servers under maintenance
  • Balance between varying cluster sizes
  • A/B testing

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Latency-based Routing

Route users to the DNS server with the lowest latency.

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Geolocation-based Routing

Route users based on their geographic location.
  • 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).
DNS introduces a slight delay but caching significantly mitigates this impact. Choose managed DNS services for complex routing requirements.

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Source(s) and Further Reading

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