Webhook vs. WebSocket vs. Pub/Sub vs. API Polling: How to Choose the Right Approach
In today's software industry, particularly web development, communication and data exchange between systems are essential. This communication may occur between a client and a server within the same system, between different servers, or even with third-party services. When real-time communication is required, the challenges become even more complex.
Webhook, WebSocket, Pub/Sub, and API Polling are common approaches to real-time data exchange. Developers can choose among them based on different requirements and goals. As an engineer, it's crucial to use the right tool for the right problem. Otherwise, you risk overengineering a solution or applying a particular technology where it isn't necessary.
In this article, we'll start by exploring how each approach works. Then, we'll compare them with other data-sharing techniques used in modern architectures and identify the scenarios in which each technique is most appropriate.
Finally, we'll answer the question that might be causing you the most headaches: When should you use webhooks, WebSockets, Pub/Sub, or API polling?
1. API Polling
1.1 What Is an API?
API, short for Application Programming Interface, is a set of protocols that allows different software components to communicate and exchange data.
An API, which stands for application programming interface, is a set of protocols that enable different software components to communicate and transfer data.Source: What Is an API? β Postman
An API serves as an application's gateway to the outside world. It provides an interface through which other systems can interact with the application. The application can expose as much functionality as it needs while keeping the rest of its internal implementation abstracted away.
APIs typically consist of a collection of endpoints that clients can call to interact with a system. This communication often uses HTTP methods in RESTful APIs, such as GET, POST, PUT, and DELETE, and may include information describing the action the client wants to perform.
Further reading:
1.2 What Is API Polling?
API polling is a technique in which a client repeatedly sends requestsβtypically HTTP GET requestsβto a server to check whether new information or updates are available.
Simply put, the client sends requests to the server at regular intervals, such as every few seconds or minutes, to retrieve the latest data.
Compared with other real-time communication techniques, polling is generally less efficient because it generates additional network traffic and can introduce delays in data delivery. However, it can still be useful when WebSockets or other real-time mechanisms aren't feasible due to infrastructure limitations or a lack of client-side support.
2. Webhooks
A webhook is a user-defined callback mechanism built on HTTP that enables communication between two applications or APIs.
Webhooks commonly use JSON as their payload format, with requests typically sent via HTTP POST.
Webhook communication works by sending an HTTP request from a source application to a destination application. When an event occurs in the source application, an HTTP request containing relevant event data is triggered and sent to an endpoint in the destination application, commonly known as the webhook URL.
Webhooks are considered an event-driven communication mechanism. Many popular SaaS platforms support webhooks, allowing other systems to react to events. Examples include GitHub Webhooks, Twilio Webhooks, Stripe Webhooks, Slack Webhooks, and Shopify Webhooks.
Webhook requests are commonly sent using HTTP POST, although some providers may support other methods, such as GET. The supported methods and implementation details depend on the provider and are documented in its technical documentation.
Webhooks are relatively straightforward to implement. The receiving system needs to expose an endpoint that accepts incoming requests and follows the interface expected by the sending system.
When an update occurs, the receiving system doesn't need to repeatedly actively poll the source API. Instead, it can passively receive a request from the source system whenever a relevant event takes place.
3. WebSocket
WebSocket is a computer communication protocol that provides full-duplex communication channels over a TCP connection.
WebSocket is a communications protocol that supports full-duplex communication over a persistent connection.References:
In a full-duplex connection, both devices can send and receive data simultaneously. Think of a phone conversation: both participants can speak and listen at the same time without waiting for the other person to finish speaking.
Unlike traditional HTTP request-response communication, in which the client initiates a request and the server responds, WebSocket allows both the client and server to send messages at any time once the connection has been established.
This enables bidirectional, real-time data exchange without repeatedly establishing new connections. WebSockets are particularly well suited to applications that require continuous updates, such as chat applications, online games, and collaborative tools.
WebSocket enables real-time, two-way communication between networked systems by maintaining an open connection between the client and server for the duration of the session.
This creates a full-duplex communication channel through which both parties can exchange information with minimal additional latency.
4. Pub/Sub
Pub/Sub, short for Publish/Subscribe, is a messaging pattern in which publishers categorize messages, and subscribers receive messages based on the topics or categories to which they subscribe.
In a Pub/Sub system, publishers don't send messages directly to individual subscribers. Instead, messages are published to channels or topics, and subscribers interested in a particular topic receive the corresponding messages.
With Pub/Sub, data can flow through complex pipelines from one producer to a single consumer, a group of consumers, or many different consumers. Messages are organized by topics and distributed through a messaging system or message broker.
This decouples senders from receivers, enabling efficient message distribution to multiple subscribers. Pub/Sub is commonly used to broadcast events or data to multiple clients or services. Examples include real-time updates on social media platforms and notifications from IoT devices.
Popular systems and technologies that support Pub/Sub include RabbitMQ, Kafka, and Redis Pub/Sub.
5. When Should You Use Each Approach?
5.1 API Polling
Polling is a good choice when you don't need immediate real-time updates, especially when data changes frequently and reacting to every individual change could overwhelm your system.
Imagine you're running a successful startup, and your user base is growing by hundreds of users every second. You want to display the current number of subscribers on a large screen in the middle of your office.
Fetching the latest count every time a new user registers would be unnecessarily expensive and could generate excessive traffic.
Instead, you could poll the server every five to ten minutes to retrieve the current total number of users. This reduces the system's workload and consumes fewer resources.
5.2 Webhooks
Webhooks are a simple communication pattern. Consider using them when you need:
- One-way, event-driven communication from a source to a destination.
- Communication between two systems, such as server-to-server integrations, without maintaining a continuous connection.
- An immediate response to an event generated by a SaaS application that supports webhooks.
- A push-based mechanism for delivering updates as soon as relevant events occur.
- One-to-one communication between a source system and a receiving endpoint.
5.3 WebSocket
Use WebSockets when you need bidirectional communication between two networked systems, such as when building a chat application.
WebSockets are also useful for dashboards and data visualization tools that need to reflect changing values in real time.
5.4 Pub/Sub
Use a Pub/Sub system when multiple consumers are interested in the same message, when you have multiple message producers, or when you want to process messages asynchronously.
Consider an e-commerce website as an example. When a customer places an order, you may need to email an invoice to the customer, notify the shipping department, and record the sale in a CRM system.
Imagine that these responsibilities are handled by three separate services: an email service, a shipping service, and a sales-record service.
All three services are interested in the same event. You can publish an order-related message to a Pub/Sub system, which then distributes it to the three subscribed services.
This allows each service to process the event independently without requiring the order-processing service to communicate directly with every downstream service.
6. Conclusion
Each of these approaches has its own advantages and is suited to different use cases. Choosing the right one depends on several factors, including the nature of your application, the level of real-time interaction required, the available resources, and the technical constraints of your environment.
Knowing which tools to use to solve a problem is what distinguishes good engineers. A technique doesn't automatically become the best choice simply because it's simple, sophisticated, or widely adopted.
Some approaches are easy to implement but may not be the most appropriate solution for the problem at hand. Understanding the strengths and limitations of each approach will help you identify where and when to apply it effectively.