What is Idempotency?

In plain English:

Idempotency means you can do the same action again and again and the result will be exactly the same — like pressing a calm and understanding button.

It's like telling your friend Kahnu, “Please switch on the light.”

• If it’s off, he turns it on. ✅
• If it’s already on, he shrugs and walks away. ✅
• If you tell him again, he still doesn’t mess with it. ✅

Kahnu is idempotent. Be like Kahnu.

🎭 Real-Life Examples

• 🔁 Elevator Button: No matter how many times you press it, the elevator doesn’t arrive faster. (Sorry.)
• 🔐 Unlocking Your Phone: Once it's unlocked, unlocking again does nothing — it’s already unlocked.
• 📤 Resending an Email: If your app is smart and knows you already sent the email, it just says, “Cool, already done.”
• 💸 Online Payments: You hit 'Pay' once. It times out. You panic and click again. Idempotency ensures you don’t donate your rent money to Amazon.

🧾 Why Does It Matter?

• 💣 Avoid duplicate operations (e.g., multiple charges or duplicate records)
• 🚦 Network retries are a thing. The frontend or backend might retry a request if it doesn’t get a response.
• 💼 Users are impatient. They double-click EVERYTHING.
• 🧪 System reliability and data consistency — two things developers and coffee have in common.

🧙‍♀️ Where Is It Used?

• Payment systems
• Booking systems
• Form submissions
• APIs with POST/PUT/PATCH methods
• Anything involving money, legal records, or Kahnu’s dating app (which accepts only one love letter per user).

🛠 How to Implement Idempotency

The Secret Ingredient: An Idempotency Key

Every request gets a unique token, like:

Idempotency-Key: user123-payment-20240503

The server stores the result of the first request and associates it with the key. If the same key is received again:

• It doesn't repeat the operation.
• It simply returns the stored result.

In Code (Pseudocode):

if (request.hasIdempotencyKey() && store.exists(key)) {
  return store.getResult(key);
} else {
  const result = performOperation();
  store.save(key, result);
  return result;
}

Simple. Elegant. Prevents panic-induced chaos.

🎓 Kahnu’s Wild Ride

Kahnu once built a payment system without idempotency. One user paid for a ₹99 plan... 27 times. The customer is now a shareholder.

Lesson learned.

🔁 Idempotent vs Non-Idempotent Methods

HTTP Method	Idempotent?	Example
GET	✅ Yes	/users/1
PUT	✅ Yes	Replace user data
DELETE	✅ Yes	Delete same user again = same result
POST	❌ No	Submitting form = multiple records

To make POST idempotent, use an idempotency key.

⚠️ Gotchas

• Not all operations can safely be made idempotent.
• Storing keys and results = extra storage needs.
• Expiry of idempotency keys must be planned.
• Side-effects (like sending emails or SMS) can still sneak through. ☠️

🧩 When to Use Idempotency

Use it when:

• Users can click or tap repeatedly like caffeinated squirrels 🐿️
• The network can flake out (aka, the usual scenario)
• Operations cost time or money

Avoid it when:

• You want repeated actions to do different things (e.g., rolling dice)

🎯 Real World Analogy: Kahnu's Netflix Account

• Kahnu hits 'Download' on a movie.
• Wi-Fi dies halfway.
• He tries again.
• Netflix doesn’t re-download from scratch. It picks up where it left off or reuses the cached file.

Netflix is smart. Be like Netflix.

📚 Summary

• Idempotency = Press the same button, get the same result.
• It’s the backbone of safe retries and peaceful APIs.
• Add it where it matters: payments, forms, bookings.
• Use an idempotency key to identify operations.

🔮 Final Words from Kahnu

“Click once. Chill twice.”

Idempotency keeps apps cool, developers sane, and bank accounts accurate.