System requirements

Functional:

1. Input a text and return a URL
2. Open URL and show previous stored text

Non-Functional:

1. Synchronous API
2. Low-latency
3. High available

Capacity estimation

1. 100 writes per second
2. 500 reads per second

API design

System will provide 2 APIs. One endpoint to receive the text to be stored, and a second endpoint to receive a code and return the text.

Backend is decoupled from front-end developed as RESTful API.

# Save text endpoint

POST /text {text: "my-text"}

Response:

HTTP Status Code: 201

Payload: {url: "https://my-pastebin.com/:unique-code", expires_at: "timestamp"}

# Get text endpoint

GET /text/:code

Response:

HTTP Status Code: 200

Payload: {text: "my-text"}

Database design

Store data on postgres with replicaset. Setup connection pool on app connections.

texts table:

• id int serial PK
• code varchar 10 (maps to text) => index btree
• data text => original value sent by user
• expires_at timestamp
• created_at timestamp

High-level design

1. Write flow, text-service handles all backend. When saving a text, it generates a unique key using a global counter on Redis plus random values, hashing with a base62 algo to produce a short code. The code is the key to map to original text received. Also, caches the key=>text into Redis with a 1hour TTL
2. Read flow, text-service receive the code and fetches redis. If cache miss, fallback to postgres replica.

Request flows

Explain how the request flows from end to end in your high level design. Also you could draw a sequence diagram using the diagramming tool to enhance your explanation...

Detailed component design

Dig deeper into 2-3 components and explain in detail how they work. For example, how well does each component scale? Any relevant algorithm or data structure you like to use for a component? Also you could draw a diagram using the diagramming tool to enhance your design...

Trade offs/Tech choices

Explain any trade offs you have made and why you made certain tech choices...

Failure scenarios/bottlenecks

Try to discuss as many failure scenarios/bottlenecks as possible.

Future improvements

1. Add collaborative editing with real-time changes