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🔔 Webhooks Deep Dive: Real-Time Communication Between Services

Webhooks are a lightweight, efficient way for applications to notify each other of events in real-time by sending HTTP POST requests to predefined URLs.

They are event-driven, push-based alternatives to polling, commonly used in APIs like Stripe, GitHub, Slack, and many others.

🚀 What is a Webhook?

A webhook is a mechanism where one system (sender) automatically sends an HTTP request (usually POST) to another system (receiver) when a certain event occurs.

🔁 How It Works

Client registers a webhook URL with the provider.
Event happens (e.g., payment succeeded).
Provider sends HTTP POST to the webhook URL with event payload.
Client processes the event.

🧪 Webhook Example: Stripe Payment

📤 Stripe Sends Webhook

POST /webhook
Content-Type: application/json
Stripe-Signature: t=162890...

{
  "id": "evt_123",
  "type": "payment_intent.succeeded",
  "data": {
    "object": {
      "id": "pi_456",
      "amount": 5000
    }
  }
}

📥 Your App Receives It

@app.route("/webhook", methods=["POST"])
def handle_webhook():
    event = request.get_json()
    if event["type"] == "payment_intent.succeeded":
        handle_success(event["data"]["object"])
    return "", 200

🔐 Webhook Security

Since webhooks are open endpoints, they need to be protected.

✅ Best Practices

Verify signatures (e.g., HMAC or API provider secret)
Use HTTPS only
Restrict by IP or firewall if possible
Rate-limit and throttle
Do not trust user input

🔹 HMAC Signature Verification (Node.js Example)

const crypto = require("crypto");

function verifySignature(payload, header, secret) {
  const hmac = crypto.createHmac("sha256", secret);
  hmac.update(payload, "utf8");
  const digest = hmac.digest("hex");
  return digest === header;
}

📦 Payload Format

JSON is the standard format.
Typically includes:
- event or type
- timestamp
- data object
- id of the event

Always refer to the provider’s docs for exact payload structure.

📈 Reliability & Best Practices

Webhooks are fire-and-forget by design. To ensure robustness:

✅ Best Practices for Consumers

Return 2xx quickly (e.g., 200 OK) even if async processing
Queue webhook events for durable background jobs
Handle duplicates (idempotency is key)
Implement retries and dead-letter queues
Log and monitor events received

✅ Best Practices for Providers

Retry failed requests with exponential backoff
Document webhook structure and behavior
Provide test utilities (e.g., GitHub/Stripe simulators)
Allow secret rotation

🧰 Tools for Working with Webhooks

Tool	Purpose
ngrok	Expose local server to receive webhooks
Webhook.site	Test and inspect HTTP requests
RequestBin	Temporary endpoint for debugging
Postman	Create mock endpoints & simulate payloads
Svix	Hosted webhook management platform

🔄 Webhooks vs Polling vs Pub/Sub

Feature	Webhooks	Polling	Pub/Sub (e.g., Kafka)
Push-based	✅	❌	✅
Real-time	✅	❌	✅
Easy to set up	✅	✅	❌
Scalable	⚠️ (needs infra)	✅	✅
Durable	❌	✅	✅

Use webhooks for simple integrations, and Pub/Sub or message queues for high-volume or critical systems.

🧩 Real-World Use Cases

Stripe: payment_intent.succeeded
GitHub: push, pull_request, issues
Slack: custom slash commands and bots
Shopify: order creation, cart updates
Zapier: webhook-based integrations

✅ Checklist: Webhook Consumer

[x] HTTPS endpoint
[x] Signature verification
[x] Return 2xx response immediately
[x] Deduplicate events using id
[x] Use retry + logging mechanism
[x] Queue events for background processing

📚 Resources

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