npm package: @ibm-functions/composer
Description: Composer is a new programming model for composing cloud functions built on Apache OpenWhisk.
Author: Olivier Tardieu
Latest version: 1.0.0

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# @ibm-functions/composer

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Composer is a new programming model for composing cloud functions built on
[Apache OpenWhisk](https://github.com/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](https://github.com/apache/openwhisk/blob/master/docs/conductors.md)
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](composer.js) Node.js module for authoring compositions using
  JavaScript,
* the [compose](bin/compose.js) and [deploy](bin/deploy.js)
  [commands](docs/COMMANDS.md) for compiling and deploying compositions,
* [documentation](docs), [examples](samples), and [tests](test).

## Installation

Composer is distributed as Node.js package. To install this package, use the
Node Package Manager:
```
npm install -g @ibm-functions/composer
```
We recommend installing the package globally (with `-g` option) if you intend to
use the `compose` and `deploy` commands to compile and deploy compositions.

## Defining a composition

A composition is typically defined by means of a JavaScript expression as
illustrated in [samples/demo.js](samples/demo.js):
```javascript
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](docs/COMBINATORS.md) methods.
These methods implement the typical control-flow constructs of an 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 takes 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 shortened
 to:
```javascript
composer.if('authenticate', 'success', 'failure')
```

## Deploying a composition

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.

## Running a composition

The `demo` composition may be invoked like any action, for instance using the
[IBM Cloud CLI](https://cloud.ibm.com/docs/cli):
```
ibmcloud fn action invoke demo -p password passw0rd
```
```
ok: invoked /_/demo with id 09ca3c7f8b68489c8a3c7f8b68b89cdc
```
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:
```
ibmcloud fn activation result 09ca3c7f8b68489c8a3c7f8b68b89cdc
```
```json
{
    "message": "failure"
}
```
### Execution traces

This invocation creates a trace, i.e., a series of activation records:
```
ibmcloud fn activation list
```
<pre>
Datetime            Activation ID                    Kind     Start Duration   Status  Entity
2019-03-15 16:43:22 e6bea73bf75f4eb7bea73bf75fdeb703 nodejs:10 warm  1ms        success guest/demo:0.0.1
2019-03-15 16:43:21 7efb6b7354c3472cbb6b7354c3272c98 nodejs:10 cold  31ms       success guest/failure:0.0.1
2019-03-15 16:43:21 377cd080f0674e9cbcd080f0679e9c1d nodejs:10 warm  2ms        success guest/demo:0.0.1
2019-03-15 16:43:20 5dceeccbdc7a4caf8eeccbdc7a9caf18 nodejs:10 cold  29ms       success guest/authenticate:0.0.1
2019-03-15 16:43:19 66355a1f012d4ea2b55a1f012dcea264 nodejs:10 cold  104ms      success guest/demo:0.0.1
2019-03-15 16:43:19 09ca3c7f8b68489c8a3c7f8b68b89cdc sequence warm  3.144s     success guest/demo:0.0.1
</pre>

The entry with the earliest start time (`09ca3c7f8b68489c8a3c7f8b68b89cdc`)
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 (`5dceeccbdc7a4caf8eeccbdc7a9caf18` and
`7efb6b7354c3472cbb6b7354c3272c98`). 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](https://github.com/apache/openwhisk/blob/master/docs/conductors.md)
explains execution traces in greater details.

While composer does not limit in principle the length of a composition,
OpenWhisk deployments typically enforce a limit on the number of action
invocations in a composition as well as an upper bound on the rate of
invocation. These limits may result in compositions failing to execute to
completion.

## Parallel compositions with Redis

Composer offers parallel combinators that make it possible to run actions or
compositions in parallel, for example:
```javascript
composer.parallel('checkInventory', 'detectFraud')
```

The width of parallel compositions is not in principle limited by composer, but
issuing many concurrent invocations may hit OpenWhisk limits leading to
failures: failure to execute a branch of a parallel composition or failure to
complete the parallel composition.

These combinators require access to a Redis instance to hold intermediate
results of parallel compositions. The Redis credentials may be specified at
invocation time or earlier by means of default parameters or package bindings.
The required parameter is named `$composer`. It is a dictionary with a `redis`
field of type dictionary. The `redis` dictionary specifies the `uri` for the
Redis instance and optionally a certificate as a base64-encoded string to enable
TLS connections. Hence, the input parameter object for our order-processing
example should be:
```json
{
    "$composer": {
        "redis": {
            "uri": "redis://...",
            "ca": "optional base64 encoded tls certificate"
        }
    },
    "order": { ... }
}
```

The intent is to store intermediate results in Redis as the parallel composition
is progressing. Redis entries are deleted after completion and, as an added
safety, expire after twenty-four hours.

# OpenWhisk SSL configuration

Additional configuration is required when using an OpenWhisk instance with
self-signed certificates to disable SSL certificate validation. The input
parameter object must contain a parameter of type dictionary named `$composer`.
This dictionary must contain a dictionary named `openwhisk`. The `openwhisk`
dictionary must contain a field named `ignore_certs` with value `true`:
```json
{
    "$composer": {
        "openwhisk": {
            "ignore_certs": true
        }
    },
    ...
}
```

This explicit SSL configuration is currently only necessary when using parallel
combinators or the `async` combinator.

# Installation from Source

To install composer from a source release, download the composer source code
from [our GitHub repo](https://github.com/ibm-functions/composer/releases),
rename the release tarball to `composer.tgz` and install it with command:
```shell
npm install -g composer.tgz
```