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mediumSystem Design

Why prefer stateless services and how do you handle sessions?

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01

Understand the problem

Explain statelessness.

statelesssessions
02

Attempt it yourself

Sketch your approach before reading the solution — that's what interviews test.

Nudge consolestandby

Stuck? Beam a request up — the console returns a conceptual nudge that guides your logic without spoiling the implementation.

03

Study the solution

Step 1: Outline use cases and constraints

Gather requirements and scope the problem. Ask questions to clarify use cases and constraints. Discuss assumptions.

Use cases

We'll scope the problem to handle only the following use cases

  • User needs to understand stateless to make architecture decisio

Solution ready — 2 min read

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04

Read the code

Stateless signed session token
Run Playground
import hmac, hashlib, base64

SECRET = b"server-secret"     # shared by every instance

def issue(user_id):
    payload = ("user=" + str(user_id)).encode()
    sig = hmac.new(SECRET, payload, hashlib.sha256).hexdigest()[:12]
    return base64.urlsafe_b64encode(payload).decode() + "." + sig

def verify(token):
    raw, sig = token.split(".")
    payload = base64.urlsafe_b64decode(raw)
    expected = hmac.new(SECRET, payload, hashlib.sha256).hexdigest()[:12]
    return payload.decode() if hmac.compare_digest(sig, expected) else None

t = issue(42)
print("token   :", t)
print("verify  :", verify(t))            # ANY stateless instance can validate it
print("tampered:", verify(t[:-1] + "x")) # None -> rejected
05

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