What is Domain Naming System (DNS) – 03/Apr/2021

What is Domain Naming System

• How DNS Works

• DNS Servers fall into one of the four categories

  • root nameservers:
    • A root server accepts the resolvers query which includes a domain name and the root nameserver responds by directing the recursive resolver to a TLD Name server
  • TLD (Top level Domain) nameservers:
    • This TLD name server maintains information of all the domain names that share a common extentsion (.com, .net)
    • TLD Nameserver would responding by pointing to the authorative nameserver for the domain
  • Authoritave name servers:
    • This name server contains the inforamation specific to the domain it servers. This provides the response by the records it found in this server
  • Recursive Resolvers:
    • This is the first step in DNS query

• The Process from our end is to

  • Purchase a domain
  • When we purchase domain we get the information about the name server
  • With the Domain Seller we need to add additional information so that when authoritave server is asked about our domain it responds back with ipaddress of the server where our application is running

• DNS Zone:

  • DNS is broken up into many different zones
  • A DNS zone is a portion of DNS namespace that is managed by specific orgnaiziation or administrator

• Every DNS Server has a DNS Record

DNS Records

• DNS Records (Zonefile) are instrcutions that live in Authoritave DNS Servers and provide information about a domain
• In Authorative Server we have DNS Records and most common record types are
  • A record: This record holds IP Address of a domain
  • CName record: This consists of alias name record
  • MX Record: This record consists of email server information
  • TXT Record: This lets admin store text in the record
  • NS record: Stores the nameserver for a DNS entry
  • SOA record: Stores admin information about a domain
  • SRV record: Specifies port for specific services

A Record

• The A stands for address.

CNAME record

• The canonical name is an alias of another domain

Load Balancers

• Basic Loadbalancer architecture

• There are two types of load balancers

  • Layer 4 loadbalancer
  • Layer 7 loadbalancer

• To understand this lets look at OSI Model

• Layer 4 loadbalancer

• Layer 7 loadbalancer

JSON and YAML Tutorial

Refer Here

JMES Path

• To query the JSON we have a query language which is referred as jmes path
• Refer Here for jmes path tutorial
• Write a JMESPath Expression to Refer Here for json
  • find the subnet ids of Availability zone us-west-2a

  Subnets[?AvailabilityZone=='us-west-2a'].SubnetId
  

  • find the subnet id and Vpc Id and Avaialability Zone id of subnets in AZ us-west-2b

  Subnets[?AvailabilityZone=='us-west-2b'].{"SubnetId": SubnetId, "VpcId": VpcId}
  

• Note : Try to visualize using Refer Here and JMES path expression check in JMESPath.org