Composer is now part of the Apache OpenWhisk incubator project. The Composer code is now hosted at https://github.com/apache/incubator-openwhisk-composer. Issues and pull requests should be filed against the new repository.

Composer is a new programming model for composing cloud functions built on Apache OpenWhisk. With Composer, developers can build even more serverless applications including using it for IoT, with workflow orchestration, conversation services, and devops automation, to name a few examples.

Composer synthesizes OpenWhisk conductor actions to implement compositions. Compositions have all the attributes and capabilities of an action, e.g., default parameters, limits, blocking invocation, web export.

This repository includes:

• the composer Node.js module for authoring compositions using JavaScript,
• the compose and deploy commands for compiling and deploying compositions,
• documentation, examples, and tests.

Composer is distributed as Node.js package. To install this package, use the Node Package Manager:

npm install -g @ibm-functions/composer

We recommend to install the package globally (with -g option) if you intend to use the compose and deploy commands to compile and deploy compositions.

A composition is typically defined by means of a Javascript expression as illustrated in samples/demo.js:

const composer = require('@ibm-functions/composer')

module.exports = composer.if(
    composer.action('authenticate', { action: function ({ password }) { return { value: password === 'abc123' } } }),
    composer.action('success', { action: function () { return { message: 'success' } } }),
    composer.action('failure', { action: function () { return { message: 'failure' } } }))

Compositions compose actions using combinator methods. These methods implement the typical control-flow constructs of a sequential imperative programming language. This example composition composes three actions named authenticate, success, and failure using the composer.if combinator, which implements the usual conditional construct. It take three actions (or compositions) as parameters. It invokes the first one and, depending on the result of this invocation, invokes either the second or third action.

This composition includes the definitions of the three composed actions. If the actions are defined and deployed elsewhere, the composition code can be shorten to:

composer.if('authenticate', 'success', 'failure')

One way to deploy a composition is to use the compose and deploy commands:

compose demo.js > demo.json
deploy demo demo.json -w

ok: created /_/authenticate,/_/success,/_/failure,/_/demo

The compose command compiles the composition code to a portable JSON format. The deploy command deploys the JSON-encoded composition creating an action with the given name. It also deploys the composed actions if definitions are provided for them. The -w option authorizes the deploy command to overwrite existing definitions.

The demo composition may be invoked like any action, for instance using the OpenWhisk CLI:

wsk action invoke demo -p password passw0rd

ok: invoked /_/demo with id 4f91f9ed0d874aaa91f9ed0d87baaa07

The result of this invocation is the result of the last action in the composition, in this case the failure action since the password in incorrect:

wsk activation result 4f91f9ed0d874aaa91f9ed0d87baaa07

{
    "message": "failure"
}

This invocation creates a trace, i.e., a series of activation records:

wsk activation list

activations
fd89b99a90a1462a89b99a90a1d62a8e demo
eaec119273d94087ac119273d90087d0 failure
3624ad829d4044afa4ad829d40e4af60 demo
a1f58ade9b1e4c26b58ade9b1e4c2614 authenticate
3624ad829d4044afa4ad829d40e4af60 demo
4f91f9ed0d874aaa91f9ed0d87baaa07 demo

The entry with the earliest start time (4f91f9ed0d874aaa91f9ed0d87baaa07) summarizes the invocation of the composition while other entries record later activations caused by the composition invocation. There is one entry for each invocation of a composed action (a1f58ade9b1e4c26b58ade9b1e4c2614 and eaec119273d94087ac119273d90087d0). The remaining entries record the beginning and end of the composition as well as the transitions between the composed actions.

Compositions are implemented by means of OpenWhisk conductor actions. The documentation of conductor actions explains execution traces in greater details.