Basic System Design 🌚

For Frontend Developer

About Me

莫力全 Kyle Mo

Software Engineer @OneDegree

雜食性軟體工程師，人生不長，但也不短，有興趣的技術我都要學。

Starbugs Weekly

BESG

Why should I learn SD as a frontend engineer ? 🧐

Interview

Frontend Engineer

Backend Engineer

DevOps Engineer

Data Engineer

Software Engineer

Cloud Engineer

曾經，我也有一次系統設計的面試經驗...🙈

I think it‘s not just for the interviews. 🎃

🌚 - Ability to work with complex system

☺️ - Junior Developer -> Senior Developer

😀 - Communicate with different roles

🧐 - FE tends to need BE skills today

From Line Developer talk in conference

Distributed System 分散式系統 👌

Assume that...

How about..

And how about..

And if...

???

把剛剛的人想成網路流量，交通工具想成伺服器，我們知道單機的 Vertical Scaling 有局限性，也暴露了 Single Point Of Failure 的風險

分散式系統是一組電腦，透過網路相互連接傳遞訊息與通訊後並協調他們行為而成的系統。

運算

服務分流

儲存

只要是分散式，就要特別注意資料一致性的問題。

分散式系統是一個超級複雜的 Topic，今天只會講到皮毛，有興趣可以參考 MIT 6.824 分散式系統課程

我們希望設計出來的系統擁有哪些特性？ 👀

「效能增長程度」與「資源投入」成正比

當系統遇到的流量漸漸變大時，我們會希望系統的伺服器或儲存空間也能夠跟著擴展，避免無法負荷的狀況。

Scalability 可擴展性/可擴縮性

可靠性代表一個系統在它開始執行之後到某個時間點，系統正常執行的機率，也就是系統無故障執行的概率。

Reliability 可靠性

Availability 可用性

可用性是一個容易跟可靠性搞混的指標，它的定義為系統在面對各種異常時可以正確提供服務的能力，更嚴謹的定義為「系統服務不中斷運行時間占實際運行時間的比例。」如果以公式來看：

Availability % = (available time / total time) *100

Availability 可用性

Efficiency 高效率

Latency 延遲：執行一個操作要花費的「時間長度」。

Throughput 吞吐量：以一個時間區間作為單位，單位時間內可以執行「幾次」操作，或運算的「次數」。

High Concurrency

故名思義，代表一個系統是不是方便管理，是不是能快速迭代新功能？是不是能夠快速追蹤 bug？或是能不能把 infrastructure 抽象化，讓應用工程師可以專注在程式邏輯的開發。

Manageability 可管理性

IaC (Infrastructure as Code)

# Cloudformation example

Parameters: 
  ExistingSecurityGroup: 
    Description: An existing security group ID (optional).
    Default: NONE
    Type: String
    AllowedValues: 
      - default
      - NONE
Conditions: 
  CreateNewSecurityGroup: !Equals [!Ref ExistingSecurityGroup, NONE]
Resources: 
  MyInstance: 
    Type: "AWS::EC2::Instance"
    Properties: 
      ImageId: "ami-0ff8a91507f77f867"
      SecurityGroups: !If [CreateNewSecurityGroup, !Ref NewSecurityGroup, !Ref ExistingSecurityGroup]
  NewSecurityGroup: 
    Type: "AWS::EC2::SecurityGroup"
    Condition: CreateNewSecurityGroup
    Properties: 
      GroupDescription: Enable HTTP access via port 80
      SecurityGroupIngress: 
        - 
          IpProtocol: tcp
          FromPort: 80
          ToPort: 80
          CidrIp: 0.0.0.0/0
Outputs: 
  SecurityGroupId:
    Description: Group ID of the security group used.
    Value: !If [CreateNewSecurityGroup, !Ref NewSecurityGroup, !Ref ExistingSecurityGroup]

Key Components in SD 🧠

Cache

Proxy

Replication & Redundant

CDN

Load Balancing

Message Queue

Schema Design

Database (SQL vs NoSQL)

Partition & Sharding

DB Master-Slave

CAP Theorem

😩

Cache

Replication & Redundant

CDN

Load Balancing

Schema Design

Database (SQL vs NoSQL)

Partition & Sharding

CAP Theorem

😊

DB Master-Slave

Message Queue

Proxy

Caching 👻

Cache

Application

1. Cache Hit 直接返回

2. Cache Miss 從 DB 拿資料

3. 把資料寫進 Cache

CDN 🌍

Load Balancing 🧜‍♀️

Round-Robin

Least Connected

IP-Hash

面對系統設計時的思維走向 🐝

Step 1. 釐清系統需求

🌚 - Non-Functional Requirements

🌞 - Functional Requirements

😀 - Communicate with different roles

🧐 - FE tends to need BE skills today

Step 2. 關於系統流量、容量、網路頻寬等指標的粗略估算

DAU ? Network Traffic ? Storage Capacity ?Memory For Caching ? Read : Write = {} : {} ?.......

Step 3. 定義 System Interface

uploadVideo(user_id, video_content, video_location, user_location, ……)

addVideoToFavorite(user_id, video_id, timestamp, …….)

Step 4. 定義 Data Model | DB Schema

User: UserID, Name, Email, DoB, CreationDate, LastLogin, ….

Video: VideoID,VideoLink, VideoLocation, NumberOfLikes, TimeStamp, …

Step 5. High Level Design

Step 6. System Detailed Design

Step 7. Find Trade Off And Try To Solve It

Never feel that your design is perfect

Let's design a Netflix like streaming system 🙈

Step 1. 釐清系統需求

🌞 - Functional Requirements

Users should be able to upload videos
Users should be able to share and view videos.
Users should be able to perform searches based on video titles.
Our services should be able to record stats of videos, e.g., likes/dislikes, total number of views, etc.
Users should be able to add and view comments on videos.

Step 1. 釐清系統需求

🌚 - Non-Functional Requirements

The system should be highly reliable, any video uploaded should not be lost.
The system should be highly available. Consistency can take a hit (in the interest of availability); if a user doesn’t see a video for a while, it should be fine.
Users should have a real-time experience while watching videos and should not feel any lag.

Step 2. 關於系統流量、容量、網路頻寬等指標的粗略估算

Total users: 1.5 Billion

DAU: 800 Million

A user view 5 videos per day on average

So, the total video view per second of our system will be...

800M * 5 / 86400 sec => 46K videos/sec

Step 2. 關於系統流量、容量、網路頻寬等指標的粗略估算

upload : view ratio => 1 : 200

46K / 200 => 230 videos/sec

230 videos uploaded per second

What about Storage ?

every minute 500 hours worth of videos are uploaded to our system

One minute of video needs 50MB of storage

Total storage needed for videos uploaded in a minute would be ...

500 hours * 60 min * 50MB => 1500 GB/min (25 GB/sec)

Step 2. 關於系統流量、容量、網路頻寬等指標的粗略估算

What about Bandwidth ?

With 500 hours of video uploads per minute , assuming uploading each minute of the video takes 10MB of the bandwidth, we would be getting 300GB of uploads every minute.

500 hours * 60 mins * 10MB => 300GB/min (5GB/sec)

Assuming an upload:view ratio of 1:200, we would need 1TB/s outgoing bandwidth.

Step 3. 定義 System Interface