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abantej/aws-route53-notes.md

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aws-route53-notes.md

What is DNS?

  • DNS is used to convert human-friendly domain names (abantej.github.io) into an internet protocol (185.199.108.153) address
  • IP addresses are used by computers to identify each other on the network. IP addresses commonly come in 2 different forms, IPv4 and IPv6

IPv4

  • 32 bit field with over 4 billion different addresses (4,294,967,296)

IPv6

  • 128 bit field with 340 undecillion addresses (340,282,366,920,938,463,463,374,607,431,768,211,456)

Top Level Domains

  • .com, .edu, .gov
  • top level domain names are controlled by the Internet Assigned Numbers Authority (IANA) in a root zone database which is essentially a database of all available top level domains. (http://www.iana.org/domains/root/db)

Second Level Domains

  • .co.uk, .gov.uk, .com.au

Domain Registrars

  • an authority that can assign domain names directly under one or more top-level domains.
  • these domains are registered with InterNIC, a service of ICANN, which enforces uniqueness of domain names across the Internet
  • each domain name becomes registered in a central database known as the WhoIS database

Popular Domain Registrars

  • GoDaddy.com
  • 123-reg.co.uk
  • etc

SOA Records

  • the name of the server that supplied the data for the zone
  • the administrator of the zone
  • the current version of the data file
  • the numer of seconds a secondary name server should wait before checking for updates
  • the numer of seconds a secondary name server should wait before retrying a failed zone transfer
  • the maximum number of seconds that a secondary name server can use data before it must either be refreshed or expire
  • the default number of seconds for the time-to-live file on resource records

NS Records

  • Name Server Records
  • used by Top Level Domain servers to direct traffice to the Content DNS server which contains the authoritative DNS records

A Records

  • the fundamental type of DNS record and the "A" in A record stands for Address
  • The A record is used by a computer to translate the name of the domain to the IP address

TTL

  • Time-to-live pro
  • the length that a DNS record is cached on either the Resolving Server or the users local PC is equal to the value of the TTL in seconds
  • the lower the time to live, the faster changes to DNS records take to propagate throughout the internet

CNAMES

  • A Canonical Name (CName) can be used to resolve one domain name to another

Alias Records

  • used to map resource record sets in your hosted zone to Elastic Load Balancers, CloudFront distributions, or S3 buckets that are configured as websites
  • Alias Records work like a CNAME record in that you can map one DNS name to another target DNS name
  • key difference: a CNAME can't be used for naked domain names (zone apex record). you can't have CNAME for http://acloud.guru, it must be either an A record or an Alias
  • Alias resource record sets can save you time because Amazon 53 automatically recognizes changes in the record sets that the alias resource record set refers to

DNS 101 Exam Tips

  • ELB's do not have pre-defifned IPv4 addresses, you resolve to them using a DNS name
  • understand the difference between an Alias Record and a CNAME
  • always choose an Alias Record over a CNAME

Route 53 Routing Policies

  1. Simple
  2. Weighted
  3. Latency
  4. Fail Over
  5. Geolocation

Route 53 Routing Policies - Simple

  • the default routing policy when you
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