System Design
  • Introduction
  • Glossary of System Design
    • System Design Basics
    • Key Characteristics of Distributed Systems
    • Scalability - Harvard lecture
      • Scalability for Dummies - Part 1: Clones
      • Scalability for Dummies - Part 2: Database
      • Scalability for Dummies - Part 3: Cache
      • Scalability for Dummies - Part 4: Asynchronism
    • Trade-off
      • CAP Theorem
      • Performance vs scalability
      • Latency vs throughput
      • Availability vs consistency
    • Load Balancing
      • Load balancer
    • Proxies
      • Reverse proxy
    • Cache
      • Caching
    • Asynchronism
    • Processing guarantee in Kafka
    • Database
      • Relational database management system (RDBMS)
      • Redundancy and Replication
      • Data Partitioning
      • Indexes
      • NoSQL
      • SQL vs. NoSQL
      • Consistent Hashing
    • Application layer
    • DNS
    • CDN
    • Communication
      • Long-Polling vs WebSockets vs Server-Sent Events
    • Security
    • Lambda Architecture
  • OOD design
    • Concepts
      • Object-Oriented Basics
      • OO Analysis and Design
      • What is UML?
      • Use Case Diagrams
    • Design a parking lot
  • System Design Cases
    • Overview
    • Design a system that scales to millions of users on AWS
    • Designing a URL Shortening service like TinyURL
      • Design Unique ID Generator
      • Designing Pastebin
      • Design Pastebin.com (or Bit.ly)
    • Design notification system (scott)
      • Designing notification service
    • Designing Chat System
      • Designing Slack
      • Designing Facebook Messenger
    • Design Top K System
    • Designing Instagram
    • Design a newsfeed system
      • Designing Facebook’s Newsfeed
      • Design the data structures for a social network
    • Designing Twitter
      • Design the Twitter timeline and search
      • Designing Twitter Search
    • Design Youtube - Scott
      • Design live commenting
      • Designing Youtube or Netflix
    • Designing a Web Crawler
      • Designing a distributed job scheduler
      • Designing a Web Crawler/Archive (scott)
      • Design a web crawler
    • Designing Dropbox
    • Design Google Doc
    • Design Metrics Aggregation System
      • Design Ads Logging System
    • Design Instacart
    • Design a payment system
      • Airbnb - Avoiding Double Payments in a Distributed Payments System
    • Design Distributed Message Queue
      • Cherami: Uber Engineering’s Durable and Scalable Task Queue in Go
    • Design Distributed Cache
      • Design a key-value cache to save the results of the most recent web server queries
    • Design a scalable file distribution system
    • Design Amazon's sales ranking by category feature
    • Design Mint.com
    • Design Autocomplete System
      • Designing Typeahead Suggestion
    • Designing an API Rate Limiter
      • Designing Rate Limiter
    • Design Google Map
      • Designing Yelp or Nearby Friends
      • Designing Uber backend
    • Designing Ticketmaster
      • Design 12306 - Scott
    • Design AirBnB or a Hotel Booking System
  • Paper Reading
    • MapReduce
  • Other Questions
    • What happened after you input the url in the browser?
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  • Introduction
  • Algorithm
  • Disadvantages

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  1. Glossary of System Design

DNS

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Last updated 5 years ago

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Introduction

A Domain Name System (DNS) translates a domain name such as www.example.com to an IP address.

DNS 就是一个翻译机，把网址转换成 IP 地址

DNS is hierarchical, with a few authoritative servers at the top level. Your router or ISP provides information about which DNS server(s) to contact when doing a lookup. Lower level DNS servers cache mappings, which could become stale due to DNS propagation delays. DNS results can also be cached by your browser or OS for a certain period of time, determined by the time to live (TTL).

  • NS record (name server) - Specifies the DNS servers for your domain/subdomain.

  • MX record (mail exchange) - Specifies the mail servers for accepting messages.

  • A record (address) - Points a name to an IP address.

  • CNAME (canonical) - Points a name to another name or CNAME (example.com to www.example.com) or to an A record.

Services such as CloudFlare and Route 53 provide managed DNS services. Some DNS services can route traffic through various methods:

Algorithm

  • Prevent traffic from going to servers under maintenance

  • Balance between varying cluster sizes

  • A/B testing

  • Latency-based

  • Geolocation-based

round robin 基本上就是 equally distribute request。所有在 pool 里的 host 挨个接收 request。而 weighted round robin 做了改进，比如有三个 hosts，他们的 weight 分别是 6:3:1。那么 每十个 requests，6 个 dispatch 到 host1，3 个 dispatch 到 host2，1 个 dispatch 到 host3。这在 hosts 他们的性能不一样的时候优化的效果明显。

Disadvantages

  • Accessing a DNS server introduces a slight delay, although mitigated by caching described above.

  • DNS server management could be complex and is generally managed by governments, ISPs, and large companies.

  • DNS services have recently come under DDoS attack, preventing users from accessing websites such as Twitter without knowing Twitter's IP address(es).

Weighted round robin