Webhooks were introduced as the communication bridge between third-party service providers and consumers/application providers, to send callback data back to application providers when events occurred at the service provider’s end – thereby enabling effective realtime messaging.
What is a webhook ?
A webhook is an HTTP request, triggered by an event in a source system and sent to a destination system, often with a payload of data. Webhooks are automated, in other words they are automatically sent out when their event is fired in the source system.
What are webhooks used for ?
Used to communicate the occurrence of an event in one system to another system, and they often share data about the event.
Let's say you subscribe to a streaming service. The streaming service wants to send you an email at the beginning of each month when it charges your credit card.
The streaming service can subscribe to the banking service (the source) to send a webhook when a credit card is charged (event trigger) to their emailing service (the destination). When the event is processed, it will send you a notification each time your card is charged.
The banking system webhooks will include information about the charge (event data), which the emailing service uses to construct a suitable message for you, the customer.
How webhooks work ?
Webhook request process
Common in SaaS platforms like GitHub, Shopify, Twilio etc… because they support different types of events based on the activities that happen within them. To receive webhook requests, you have to register for one or more of the events (also known as topics) for which the platform offers a webhook. A webhook request will be sent to a destination endpoint (URL). It can be your application, register the URL as the Webhook URL for that event.Once the webhook registration for an event is complete, you will receive webhook requests at the destination URL you provided each time the event occurs.
Consuming a webhook
After the registration, we can receive the webhook requests : regular http requests, webhook payloads are serialized form-encoded JSON or XML format, one way-communication system, can be distributed to multiple destinations that require information, request can be sent more than once making it idempotent.
When to use Webhook ? Comparing to WebSocket, Pub/Sub, Polling and API
Webhook vs WebSocket
WebSockets are used to facilitate two-way real-time communication between two networked systems. WebSockets achieve this by keeping a socket open on both the client and the server for the duration of the conversation.
This opens a duplex communication stream enabling both the client and server to pass information between one another with no significant latency added.
Useful for chat app and data visualization (need to reflect real-time data values).
Webhook | WebSocket |
|---|---|
One-way communication from source to destination | 2-way communication between server and client. |
Close the socket connection on the receiving application once a response is sent back. | Keep connection open for as long as required and not just for a single transfer of info. |
Communication protocol is regular HTTP. | Communication protocol is its own WS protocol. |
Webhook vs Pub/Sub
Communication system for distributing messages between a set of publishers (message producers) and subscribers (message consumers). A pub/sub system buffers messages from producers and routes them to subscribers through the use of dedicated channels known as topics. Publishers publish messages to topics and subscribers express interest by subscribing to the topics.
Useful for e-commerce site.
Webhook | Pub/Sub |
|---|---|
Message producer is fully aware of the location of the consumer through the webhook URL. | Messages are decoupled from consumers. |
Direct form of communication between producer and consumer. | Middle-Man framework that routes messages from publishers to consumers. |
One-to-one communication. | Many producers can send messages to multiple consumers. |
Webhook vs Polling
Polling involves periodically making requests to a system to check for new events or data. If new data is found, a response is returned with the new data in its payload. If no new data is available, nothing is returned.
Polling is used to query systems for new information and can be set up as an automated cron job that runs at certain intervals.
Useful when we don’t need real-time updates.
Webhook | Polling |
|---|---|
Push model of communication. | Pull model of communication. |
Webhook requests made by a server. Automatically triggered when an event occurs. | Polling requests made by a client. Is set to run at fixed intervals and runs whether there is a new event or not. |
Requests only when there is new info. | Polling can be resource-intensive. |
Webhook vs API
An API is an application's gateway to the world. It is the interface that allows other systems to interact with the application. The application can expose as much as it wants and keep its remaining parts abstracted.
APIs are usually a collection of endpoints that clients can call to communicate with the system. This communication is done via request methods such as GET or POST, and may carry some information related to the action the client is willing to perform.
Webhook | API |
|---|---|
Make calls to APIs | API provides webhooks with the entry point to push data to an app. |
When an event occurs in a source app, a webhook request is triggered to one of the API endpoints. |