Programming model
OpenWhisk Entities
OpenWhisk uses the following entities to describe its programming model:
Action
A stateless, relatively short-running function (on the order of seconds or even milliseconds) invoked as an event handler.
Trigger
The name for a class of events. Triggers represent the events (and their data) themselves without any concept of how they were generated.
Rule
A mapping from a Trigger to an Action which may contain simple conditional logic. OpenWhisk evaluates incoming events (that belong to a Trigger) and invokes the assigned Action (event handler).
Event Source
An Event Source is the descriptor (edge) for an Event Producer (or provider). It describes the Event Format(s) produced, as well as any configuration and subscription capabilities.
Feed
A Feed is an optional service that represents and controls the stream which all belong to a Trigger. A feed provides operations called feed actions which handle creating, deleting, pausing, and resuming the stream of events. The feed action typically interacts with external services which produce the events
Package
A named, shared collection of Actions and Feeds. The goal of this specification is to describe OpenWhisk packages and their component entities and resources to enable an open-ecosystem.
Packages are designed to be first-class entities within the OpenWhisk platform to be used by tooling such as catalogs (repositories), associated package managers, installers, etc.
Note: Not all actions must belong to packages, but can exist under a namespace.
Action Composition
Action Sequence
An Action that is a sequenced composition of 2 or more existing Actions. The Action Sequence can be viewed as a named pipe where OpenWhisk can automatically take the output of a first Action ‘A’ in a declared sequence and provides it as input to the next Action ‘B’ in the sequence and so on until the sequence completes.
Note: This composition technique allows the reuse of existing action implementations treating them as “building blocks” for other Actions.
Cardinality
Trigger to Action
With the appropriate set of Rules, it's possible for a single Trigger (event) to invoke multiple Actions, or for an Action to be invoked as a response to events from multiple Triggers.
Conceptual representation
