HLDsystem_design~12 mins

DNS and how domain resolution works in HLD - Architecture Diagram

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System Overview - DNS and how domain resolution works

The Domain Name System (DNS) translates human-friendly domain names into IP addresses that computers use to identify each other on the network. It is a distributed system designed to quickly and reliably resolve domain names to IP addresses, enabling users to access websites and services by name instead of numbers.

Architecture Diagram

User
  |
  v
Local DNS Resolver
  |
  v
Root DNS Server
  |
  v
TLD DNS Server
  |
  v
Authoritative DNS Server
  |
  v
Target Website Server

Components

User

client

Initiates domain name lookup requests

Local DNS Resolver

resolver

Caches and forwards DNS queries on behalf of the user

Root DNS Server

dns_server

Directs queries to the appropriate Top-Level Domain (TLD) servers

TLD DNS Server

dns_server

Directs queries to the authoritative DNS server for the domain

Authoritative DNS Server

dns_server

Provides the IP address for the requested domain

Target Website Server

web_server

Hosts the website or service the user wants to access

Request Flow - 9 Hops

User → Local DNS Resolver

Local DNS Resolver → Root DNS Server

Root DNS Server → Local DNS Resolver

Local DNS Resolver → TLD DNS Server

TLD DNS Server → Local DNS Resolver

Local DNS Resolver → Authoritative DNS Server

Authoritative DNS Server → Local DNS Resolver

Local DNS Resolver → User

User → Target Website Server

Failure Scenario

Component Fails:Authoritative DNS Server

Impact:Domain IP address cannot be resolved, users cannot reach the website

Mitigation:Use multiple authoritative servers with failover and DNS caching at resolvers to reduce impact

Architecture Quiz - 3 Questions

Test your understanding

Which component directs the resolver to the correct Top-Level Domain server?

ALocal DNS Resolver

BRoot DNS Server

CAuthoritative DNS Server

DTarget Website Server

Design Principle

DNS uses a hierarchical and distributed design to efficiently resolve domain names by delegating responsibility across multiple server types, combined with caching to reduce latency and load.