Domain Name System (DNS)

DNS is a process of mapping a human-friendly domain name to an IP address.

  • DNS Root Servers: A group of servers to answer the root zone. Top Level Domains (TLDs) are controlled by the root zone database – Internet Assigned Numbers Authority (IANA).
  • Domain Registrars: All domain names must be unique. A registrar is an authority that can assign domain names to top-level domains and ensure its uniqueness. Each domain name becomes registered in a central database (WhoIS server).

DNS Structure

  • Top-Level Domain (TLD): the top tier in the DNS hierarchy, the last part of the domain (.com, .ca …)
  • Subdomain: Anything between a host and TLD
  • Zone, Zone file: a mapping of IPs and hosts for a given subdomain
  • Host: A record in a zone file: www, mail, …
  • Name Service: a server that runs a DNS service
  • FQDN: Fully Qualified Domain Name: host + subdomain + top-level domain

Registering a domain within DNS

  1. Check the domain is available.
  2. Purchase the domain via a registrar.
  3. Host the domain.
  4. Create records in the zone file: (www., mail., http://ftp., …)
  • Hosted Zone is a container for DNS records relating to a particular domain.
    • Public Zones: visible from Internet and VPCs
    • Private Zones: visible only from the VPCs that are associated with
      • VPC Settings: EnableDnsHostnames and EnableDnsSupport
    • Split-View DNS is supported.
      • Use the same zone name for public and private zones.
      • Provide VPC resources with different records – testing or internal application
    • NS and SOA records are created in a zone by default.

DNS Records

  • A or AAAA (Address): for a given host, provides an IP4 or IP6 address – fundamental type.
  • CNAME (Canonical Name): resolve one domain name to another; allows aliases to be created.
  • Alias: an extension of CNAME, map one DNS name (www.test.com) to another DNS name of AWS resources such as load balancers or CloudFront distributions (elb12.elb.amazonaws.com)
  • MX: the mail servers for a given domain
  • NS (Name Server): set the authoritative servers for a subdomain used by TLD servers (.com would have NS servers for test.com)
  • TXT: descriptive text in a domain – often used to verify domain ownership
  • PTR: reverse of A record, resolve a name from an IP address
  • SOA (Start of Authority): A type of resource record in the DNS containing administrative information about the zone. Every domain data starts with SOA
    • The name of the server, the administrator of the zone, the current version of the data file, the default TTL (Time to Live) on the resource records

[Note] ELB (Elastic Load Balancer) does not have a pre-defined IPv4 address. A DNS name is used to resolve the address.

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