What are Webhooks and How They Work

You may have seen webhooks integrations in a few of your applications, and you’re wondering what they are and if you should be using them. Webhooks are definitely in demand, so let’s see what exactly they are.

A webhook is an HTTP-based callback function that allows lightweight, event-driven communication between 2 application programming interfaces (APIs). Webhooks are used by a wide variety of web apps to receive small amounts of data from other apps, but webhooks can also be used to trigger automation workflows in GitOps environments. 

Basically, webhooks are used to communicate the occurrence of an event in one system to another system, and they often share data about the event.

It’s easier to understand with the help of an example: let’s say you’ve created an application using the Foursquare API that tracks when people check into your cafe/restaurant. You ideally want to be able to greet customers by name and offer a complimentary drink when they check-in.

Here, webhook notifies you when someone enters the restaurant, so you’d be able to run any processes that you had in your application once this event is triggered.

The data is then sent over the web from the application where the event originally occurred to the receiving application that handles the data.

As more and more of what we do on the web include events, webhooks are becoming more and more applicable. These are incredibly useful and resource-light ways to implement event reactions.

Now, let’s get into the process to get a better image of how webhooks work.

First of all, Webhook sends an HTTP request. To receive webhook requests, you have to register for one or more of the events/topics for which the platform offers a webhook.

Webhooks are most common in SaaS platforms like GitHub, Shopify, Stripe, Twilio, and Slack because they support different types of events based on the activities that happen within them.

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.

A single webhook request can also be distributed to multiple destinations that require the information, in a process known as fanning out. This allows source systems to speak to more applications and better distribute information across the web.

You should also make the webhook request operation at your end idempotent, as the same webhook request from some source applications can be sent more than once. In this case, you want to ensure that your response to a webhook request is not duplicated as this might lead to a compromised system.

Another thing you should know, before receiving a webhook request - you can get them as GET or POST requests, dependent on the webhooks provider. GET webhook requests are simple and have their payload appended to the webhook URL as a query string. POST webhook requests have their payload in the request body and might also contain properties like authentication tokens.

How to Configure Gitlab Webhooks?

Webhooks, as mentioned above, simplify a lot of processes on your application. They automate the pull requests, merging, pushing, and others. You can create a topic that would trigger the webhook request which will do the work for you. 

To add Webhooks in GitLab, you should:

1. Go to your GitLab account. 
2. Navigate to a repository you want to add webhooks for and find the Settings section and click on the Webhooks tab.
3. Enter the URL you want POST requests to be sent to.
4. Set the Secret Token, so the URL you send the requests to can verify that they are from GitLab.
5. Select the Trigger Events under which the webhooks should be sent. 
6. In these easy steps, you have a setup webhooks in Gitlab.

When to use Webhooks?

Now that you have a good understanding of how webhooks work, let’s see when it is then appropriate to go with webhooks.

You should use webhooks when you require the following:

• Real-time one-way communication (source→destination)
• A non-persistent connection between the connection of two systems
• You want to respond immediately to an event from a SaaS application that supports webhooks
• You want to use the push model to immediately push updates
• The communication is one-to-one

A lot of SaaS applications use webhooks for communication. For instance, Shopify uses webhooks to communicate events like when somebody updates a shopping cart or makes a sale. Stripe uses webhooks to communicate events like account updates, payments, etc. 

Famous sites that use webhooks

Notification and Information Sharing:

• Twilio webhooks convey information about events such as delivered SMS messages, voice calls, and authentication
• Slack webhooks post messages from apps into Slack
• Shopify webhooks sync with Shopify and execute code when an event takes place in your store
• Stripe webhooks notify your application when an event occurs in your account … there are many more examples.
  
  

Hopefully, this article helped you understand the advantages and limitations of the webhooks process, and the right places to implement it.