Logical Enigma
AWS Notes


  • DNS - Port 53
    • IPv4 - 32 bit field, 4 billion addresses
    • IPv6 - 128 bits
    • Internet Assigned Numbers Authority - TLD
    • Registrars - interNic, ICANN
    • Time To Live - TTL
    • SOA - Start of Authority
    • NS - Name Server
    • A - Address
    • MX, PTR (map ip to name)
    • CName - Canonical Name - map one domain name to another. Can’t be used for naked domain names (zone apex record)
    • Alias - map resource record sets in your hosted zone to AWS services. (In exam, always choose Alias record?)
    • ELBs never have a pre-defined IPv4 address, always resolve with DNS name
  • Routing
    • Simple - 1 record w/ multiple IP addresses -> return all in random order
    • Weighted - allows you to split based on weights. set-id. health checks (SNS notifications, removed from DNS until healthy)
    • Latency-based - route based on lowest network latency for user
    • Failover - for active/passive set up. primary will need health check
    • Geolocation - route based on the location of user. use cases: european customers have specific set of servers (maybe b/c configured w/ language or SLA)
    • Geoproximity - Traffic Flow Only. Bias expands or shrinks the size of the geographic region
    • Multivalue Answer - like simple routing but allows you to put health check on each record set