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Questions and Answers
What is the main advantage of using a URL shortener service, especially when sharing links through SMS or tweets?
The main advantage is that tiny URLs are exceedingly handy to share through SMS/tweets and printed materials, as they have less characters, which implies less printing cost and are easier to type.
What should you ask the interviewer when designing a URL shortener service?
You should ask the interviewer what features are expected in the service, which will then become the basis for functional requirements.
Can a customer create a custom tiny URL of their choice, and what is the maximum character limit for such URLs?
Yes, a customer can create a custom tiny URL of their choice, and the maximum character limit is 16.
What is assumed about the life span of a created URL in the system?
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What is the purpose of asking about the expected number of URL shortening requests per month?
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What is the estimated number of unique shortened links generated per second, given 100 million new URL shortenings per month?
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What is the estimated total storage requirement for the system, assuming a lifetime of 100 years and 100 million shortened links creation per month, with each data object being 500 bytes long?
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What percentage of requests are assumed to be cached, based on the Pareto Principle, and how much memory is required to cache these requests?
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What is the purpose of returning an HTTP 302 Redirect instead of an HTTP 301 Redirect, in the context of URL redirection?
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What are the two functions that should be made accessible through the REST API, and what are the parameters required for these functions?
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Study Notes
URL Shortener Service
- A URL shortener service creates a short URL (alias/tiny URL) against a long URL.
- When a user clicks on the tiny URL, they get redirected to the original URL.
- Tiny URLs are useful for sharing through SMS/tweets (due to character limits) and printing in books/magazines (reducing printing cost).
- They are also easier to type and less error-prone compared to longer URLs.
Features
- Features of a URL shortener service may include:
- Customizable tiny URL lengths
- Expiration dates for tiny URLs
- User-generated tiny URLs
- Maximum character limit for custom URLs (e.g., 16 characters)
- Metrics for most visited links
- Analytics for targeted advertisements
System Design Goals
- Functional requirements:
- Non-functional requirements:
- Performance
- Scalability
- Availability
- Security
- Non-functional requirements:
Traffic and System Capacity
- Traffic assumptions:
- 200:1 read/write ratio
- 100 million new URL shortenings per month
- 40 URLs/second generated
- 8000 URLs/second redirected (with 200:1 read/write ratio)
- Storage requirements:
- 120 billion data points/objects (assuming 100 years of service)
- 60TB of storage required (assuming 500 bytes per data object)
- Memory requirements:
- 70GB of memory required (caching 20% of 700 million requests per day)
High-Level Design
- A rudimentary design for a URL shortener service includes:
- Components for URL shortening, caching, and analytics
- Limitations of the design (to be addressed later)
Algorithm and REST Endpoints
- Two REST API functions:
- long_url: A long URL to be shortened
- api_key: A unique API key for user authentication and access control
- custom_url (optional): A custom short link URL
- Return values:
- Short URL generated or error code (if invalid parameters)
- Note: "HTTP 302 Redirect" status is used instead of "HTTP 301 Redirect" to ensure analytics tracking.
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Description
Learn about URL shortener services that create short aliases for long URLs, making it easy to share and type URLs, especially in character-limited platforms like SMS and tweets.
