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Event sources

Serverless is used to build event driven architecture. Basically everything which can trigger a function is an event. Events could be HTTP requests, events fired from a cloud storage (like a S3 bucket), scheduled events, etc.

Let's add a HTTP event to our services hello function so that the function get's called whenever a corresponding HTTP event will come in.

Adding a HTTP event

Go to the Serverless service directory and open up the serverless.yml file in your favorite editor. At first we need to add an events property to the function to tell Serverless that this function will have events attached:

functions:
  hello:
    handler: handler.hello
    events:

This events property is used to store all the event definitions for the function. Each event will be added inside this events section.

Let's add a http event with a path of greet and a method of get:

functions:
  hello:
    handler: handler.hello
    events:
      - http:
          path: greet
          method: get

That's it. There's nothing more to do to setup a http event. Let's (re)deploy our service so that Serverless will translate this event definition to provider specific syntax and sets it up for us.

(Re)deploying

We can redeploy our updated service by simply running serverless deploy again. Serverless will show the progress on the terminal and tell you once the service is updated.

Calling our HTTP endpoint

Let's test our deployed HTTP endpoint.

Open up the AWS console and navigate to the API Gateway service section. You should see a deployed API Gateway for the Serverless service.

Click on the API for the service and navigate to the resources section on the left.

You should now see the greet resource which is accessible through the /greet path and wired up to a GET HTTP method. Click on GET to open up the API endpoint. Next up click on the lightning icon with the label test.

In the next window click on the blue test button and see the result on the right hand side.

You've successfully executed the function through the HTTP endpoint!

More event sources

Serverless provides more than just a HTTP event source. You can find the full list of all available event sources with corresponding examples here.

Conclusion

Event sources are a great way to extend the functionality of your functions. They are pretty easy to setup. You simply need to add them to the corresponding function in your services serverless.yml file and (re)deploy the service.

But what if you want to add custom provider specific resources to your service which are not yet available as event sources or through plugins?

Let's take a look at this now.

Next step > Managing custom provider resources