serverless/docs/guide/event-sources.md

Event sources

With Serverless you write event driven architectures. An event can be e.g. a HTTP request, a scheduled event or even an event when someone uploads a file to your S3 bucket.

The serverless.yaml file makes it easy to add events to your functions.

Events are provider specific. Your functions can have as many events as you want it to support (even from different providers). Serverless will take care and translates the events into provider specific resources when you deploy your service to the provider of choice.

How to use event sources

Events are defined inside the function of the serverless.yaml file. Here's an example of a users function which implements an S3 bucket event for AWS and a http endpoint for Azure:

functions:
  users:
    handler: users.handler
    events:
      aws:
        s3:
          - photos
      azure:
        http_endpoints:
          direction: in
          name: req

Let's pretend we deploy this function to AWS. Serverless will create or link the photos S3 bucket with the usersfunction so the function get's triggered each time a new file is uploaded or modified in the S3 bucket.

However Serverless will create a HTTP endpoint which will trigger the function every time a request comes in if we deploy this function to Azure.

Available event sources

Serverless supports the following event sources:

AWS

Event sources for Amazon Web Services:

S3

Triggers the function every time an object is put or modified in a S3 bucket.

Examples:

functions:
  resize:
    handler: resize
    events:
      aws:
        s3:
          - photos

functions:
  users:
    handler: users.handler
    events:
      aws:
        s3:
          - photos
          - personal-files

Schedule

Schedules the function execution.

Examples:

functions:
  crawl:
    handler: crawl
    events:
      aws:
        schedule: rate(2 hours)

functions:
  aggregate:
    handler: statistics.handler
    events:
      aws:
        schedule: rate(10 minutes)

HTTP endpoint

Adds HTTP endpoints to the function.

Examples:

functions:
  create:
    handler: posts.create
    events:
      aws:
        http_endpoints:
          post: posts/create

functions:
  index:
    handler: users.index
    events:
      aws:
        http_endpoints:
          get: users