Demystifying Webhooks, WebSockets, SSE, and Event-Driven Systems

"Everything in tech these days seems to be 'event-driven'. But how do you choose between webhooks, WebSockets, or SSE when building real-time features?"

If you've ever wondered that, you're not alone.

I recently took a deep dive into how modern applications communicate in real-time — and how different mechanisms stack up depending on your use-case. Here's a breakdown of the most commonly used technologies for event-based communication: Webhooks, WebSockets, Server-Sent Events (SSE), and Pub/Sub protocols like Kafka and MQTT.

Webhooks – The Callback of the Web

Webhooks are the simplest way to notify an external system when something happens. Think of them as reverse APIs — instead of your service polling for updates, the other service pushes data to a URL you expose.

Real-world example: Stripe sends a POST request to your server when a payment is completed.

Why use them?

• Easy to implement.

• No persistent connection.

• Great for triggering background jobs, syncing data, etc.

Downsides?

• One-way only.

• No delivery guarantees unless you build retries.

• Can’t be used from the browser directly.

WebSockets – The Chatty Siblings

If your app needs two-way communication, WebSockets are your friend. They open a long-lived TCP connection between the client and server, allowing either side to send data anytime.

Use-cases:

• Chat applications

• Multiplayer games

• Collaborative tools (like Figma or Google Docs)

Pros:

• Real-time, low-latency

• Bi-directional

• Works in browsers and native apps

Cons:

• More complex than HTTP

• Needs connection handling (disconnects, retries, etc.)

SSE (Server-Sent Events) – The Underrated Gem

SSE allows the server to push updates to the browser using standard HTTP. Unlike WebSockets, it’s one-way (server → client), but it's lighter and simpler.

Best for:

• Live notifications

• Dashboards

• Real-time logs/metrics

Why I like SSE:

• Uses HTTP — plays well with proxies and firewalls.

• Built-in reconnect and event ID tracking.

• Very easy to implement in Spring Boot or Node.js.

Not ideal for:

• Bi-directional communication

• Non-browser clients

Event-Driven Architectures (Kafka, MQTT, RabbitMQ…)

When we talk about event-driven systems in microservices or IoT, we're often referring to systems that use brokers like Kafka or MQTT.

These tools let you publish and subscribe to events, enabling loose coupling between components.

Use-cases:

• Logging systems

• Distributed data processing

• IoT networks

• Async workflows

Trade-offs:

• Operational complexity (you need brokers!)

• Can be overkill for simple apps

Which one should you use?

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Quick Recap

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Final Thoughts

There's no one-size-fits-all answer. Each of these technologies has a place depending on your app’s needs. Understanding their strengths — and their limitations — is key to making the right call.