Overview

defination

the process of defining the architecture, components, modules, interfaces and data to satisfy specified requirements.

  1. conceptual design (macro)
  2. logical design
  3. physical design (micro)

Top-down design

Eg. MS Office, Huawei Security System

Bottom-up design

Most start-up use, MVP first using Medetor + MongoDb.

5 steps (SNAKE Principle):

  1. Scenario: case/interface - input
  2. Necessary: constrain/hypothesis - input
  3. Application: service/algorithm - output
  4. Kilobit: data - output
  5. Evolve - solution

A top-down example

Example one: design a radio

Step One, Scenario

  1. brain storm

    1. register/log in
    2. play music
    3. recommendation

  2. prioritize

    1. play music
      1. Get channel
      2. select a channel
      3. play

Step Two, Necessary

  1. ask

    1. total user - 100,000,000
    2. daily users - 1,000,000

  2. predict

    1. user analysis
    2. Traffic analysis
    3. Memory analysis
    4. QPS

Details:

  1. user analysis

    Avg Concurrent users = daily users / 5 = 200,000

    Peak Concurrent users = concurrent user * 3 = 600,000

    considering your product may grow in the next 3 month:

    Max Peak users in 3 month = Peak users * 10 = 6,000,000

  2. Traffic analysis

    Request of new music per user: 1 music/min

    Music size = 3MB

    Max peak traffic (in 3 months) = 6,000,000 * 3MB / 60 = 300GB/s

  3. Memory analysis

    Memory per user (metadata) = 10KB

    Max daily memory = 1,000,000 * 10 * 10 = 100 million KB = 100GB

    (10 times of avg daily user)

Step Three, Application

  1. Replay the case, one service for each
  2. Merge the services

Step Four, Kilobit: data

  1. Append 1 dataset for each service

    Eg. User service: stability, more addition, less modify and deletion.

    Eg. Channel Service: high concurrency, MongoDB

    Eg. Music Service: MP3 File Systems

Last Step, Evolve

  1. Better: constrains

    eg. able to handle 300GB/s traffic?

  2. Broader: new cases

    share music? delete user account?

  3. Deeper: details design

From views of Performance, Scalability and Robustness.