URL Shortener

Table of KEY Contents

• System Design Concept
• Finial Conclusion
• Check and Acceptance
  • Enhancement

---

Usage

start service(Local)

skaffold dev

Generate Shortened URL

curl -X POST -H "Content-Type:application/json" http://localhost/api/v1/urls -d '{"url": "<original_url>","expireAt": "2021-02-08T09:20:41Z"}'

Response

{
    "id": "<url_id>",
    "shortUrl": "http://localhost/<url_id>"
}

Redirect URL API

curl -L -X GET http://localhost/<url_id>

use 302 Redirect to original URL

System Design Concept

定義需求

• 基本要求
  • 兩隻 API
    • 產生有期限的短網址
    • 將短網址轉回長網址
      • 找不到短網址則回傳 404
• 額外限制
  • 期限最長三年
  • 短網址長度為 6 碼
  • Validation
  • Uint Test
  • Performance Test
• 附加條件
  • 使用 Go
    • 使用 Go-Kit

評估用量

• 假設短網址的效期，最長效期為 3 年
• 推估讀取比建立的 request 多，約 100:1
• 建立 request 的 QPS 預估為 100 request/s，存取的 QPS 為 10,000 request/s
• 短網址的長度為 6 個字元
  • 三年的 url mapping 總共有： $100 * 3600 * 24 * 365 * 3 \approx 10M$ 筆
  • 每一個字元可能有 62 種(0-9a-zA-Z)，所以一共可以有 $62^6 \approx 56M$
  • $56M > 10M$，所以長度 6 就足夠了
• 儲存空間至少需要 20TB
  • 依照各大瀏覽器支援的 URL 長度以及各 Web Service 的預設值，取最大相容長度為 2048
  • $(2048+6) * 10M \approx 20TB$

系統設計

• Algorithm
  • Solution 0: UUID
    • Pros:
      • simple, locally generated
    • Cons:
      • 16 characters, too long, affects DB performance
  • Solution 1: md5
    • may have collision
    • too long, need to extract first 6 characters
  • Solution 2: counter + Base62
    • Predictable
    • In a decentralized architecture is a challenge
      • a. generate within dividing ranges
      • b. pre-generated
  • Solution 3: random + Base62
    • To prevent collisions, it is needs to constantly ensure that unique
    • Keep length to 6 characters
  • Solution 4: Zookeeper
• Storage: NoSQL
  • There is no relationship between each url mapping
  • Billions of data
  • Read-heavy

Finial Conclusion

因時程考量，最終使用 random integer and base62 encoded + Redis 來設計 URL Shortener

Check and Acceptance

• 基本功能
  • 啟動服務
    • local development, run:

        skaffold dev

        minikube tunnel

  • 兩隻 API 的 happy path
    • 產生短網址, API: http://localhost/api/v1/urls, run:
    • 短網址導向, API: http://localhost/<url_id>, run:
• error handling
  • 錯誤的短網址，404
  • 錯誤的參數
• Unit Test
• Performance Test
• Technical Stack
  • Go-Kit
  • Skaffold
  • Buildpacks
  • K8s
    • minikube
  • Redis
  • Base62 Encode/Decode

Enhancement

• Step0: Unit Test & Performance Test
• Step1: Using ZooKeeper to implement a cluster shared counter
• Step2: Storage Replacement
  • Redis: 適合快速讀寫
  • DynamoDB: 巨量資料
• Step3: Scale Out

Project Layout

• single service put at internal/app
• cmd is service entry point
• internal/pkg/<shared-pkg> is shared pkg for other service

.
├── README.md
├── cmd
│   └── main.go
├── internal
│   ├── app
│   │   ├── endpoint
│   │   ├── service
│   │   └── transport
│   └── pkg 
├── go.mod
└── go.sum