| commit | 8bf8cbf2a5791004d15b0df24ef215e5b3d47f88 | [log] [tgz] |
|---|---|---|
| author | Olivier Tardieu <tardieu@users.noreply.github.com> | Mon Feb 11 10:17:53 2019 -0500 |
| committer | David Grove <dgrove-oss@users.noreply.github.com> | Mon Feb 11 10:17:53 2019 -0500 |
| tree | 295458895ed4ff37e129631d7f4bf88c819f734d | |
| parent | c58ed88f368aa0a97b06838ac3063bf7a98f2257 [diff] |
Updated doc to account for feedback on PR #16 (#20)
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:
Composer is distributed as Node.js package. To install this package, use the Node Package Manager:
npm install -g openwhisk-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('openwhisk-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 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 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.
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.
Composer offers parallel combinators that make it possible to run actions or compositions in parallel, for example:
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 $composer. It is a dictionary with a redis field of type dictionary. The redis dictionary specifies the uri for the Redis instance and optionally a certificate as a base64-encoded string to enable TLS connections. Hence, the input parameter object for our order-processing example should be:
{ "$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.
Apache OpenWhisk Composer is an effort undergoing incubation at The Apache Software Foundation (ASF), sponsored by the Apache Incubator. Incubation is required of all newly accepted projects until a further review indicates that the infrastructure, communications, and decision making process have stabilized in a manner consistent with other successful ASF projects. While incubation status is not necessarily a reflection of the completeness or stability of the code, it does indicate that the project has yet to be fully endorsed by the ASF.