Once created, the functions are available in a number of ways. They contain the code that executes in response to a trigger in order to process an event.
The first type of trigger is a pub/sub trigger. Cloud Pub/Sub is a globally distributed message bus. Functions invoked from Cloud Pub/Sub triggers will be invoked with the data (in the form of a JSON document) contained in the message that was published to the Pub/Sub topic.
Functions can also respond to notifications from Google Cloud Storage. The change notifications are triggered when objects are added, updated on deleted in the storage. The third trigger type is HTTP notifications.Functions can be invoked synchronously via an HTTP POST, and the result is be returned as the HTTP response body.
Finally, functions can be invoked directly using a call command in the Cloud Functions CLI (Command Line Interface, so you can test and debug your code.
Because Cloud Functions can be invoked by messages on a Cloud Pub/Sub topic, you can also integrate Cloud Functions with any other Google service that supports Cloud Pub/Sub as an event bus, or by using HTTP invocation with any service that provides HTTP callbacks. As this is an alpha, you have to request access if you're interest in trying it for yourself.