JavaScript (Node.js) support for Dispatch

Latest image on Docker Hub: dispatchframework/nodejs-base:0.0.8

You need a recent version of Dispatch installed in your Kubernetes cluster, Dispatch CLI configured to use it.

To add the base-image to Dispatch:

$ dispatch create base-image nodejs-base dispatchframework/nodejs-base:0.0.8

Make sure the base-image status is READY (it normally goes from INITIALIZED to READY):

$ dispatch get base-image nodejs-base

Library dependencies listed in package.json (npm dependency manifest) need to be wrapped into a Dispatch image. For example, suppose we need a math library:

$ cat ./package.json

{
    "dependencies": {
      "mathjs": "4.1.2"
    }
}

$ dispatch create image nodejs-mylibs nodejs-base --runtime-deps ./package.json

Make sure the image status is READY (it normally goes from INITIALIZED to READY):

$ dispatch get image nodejs-mylibs

Using the Node.js base-image, you can create Dispatch functions from Node.js (javascript) source files. The file can require any libraries from the image (see above).

The only requirement is: module.exports must be set to a function that accepts 2 arguments (context and payload), for example:

$ cat ./demo.js

const math = require('mathjs');
module.exports = function (context, payload) {
    return { myField: math.chain(payload.val).add(4).divide(4).done() }
};

$ dispatch create function nodejs-mylibs math-js ./demo.js

Make sure the function status is READY (it normally goes from INITIALIZED to READY):

$ dispatch get function math-js

As usual:

$ dispatch exec --json --input '{"val": 12}' --wait math-js

{
    "blocking": true,
    "executedTime": 1524612028,
    "faasId": "9ff4d69e-44e7-4ad3-a54c-6cfeb06729dd",
    "finishedTime": 1524612028,
    "functionId": "931828dc-87b8-43c7-b990-cb3f027f1e47",
    "functionName": "math-js",
    "input": {
        "val": 12
    },
    "logs": {
        "stderr": null,
        "stdout": null
    },
    "name": "28d9acec-b9c2-408c-876a-1ef14611a803",
    "output": {
        "myField": 4
    },
    "reason": null,
    "secrets": [],
    "services": null,
    "status": "READY",
    "tags": []
}

There are three types of errors that can be thrown when invoking a function:

• InputError
• FunctionError
• SystemError

SystemError represents an error in the Dispatch infrastructure. InputError represents an error in the input detected either early in the function itself or through input schema validation. FunctionError represents an error in the function logic or an output schema validation error.

Functions themselves can either throw InputError or FunctionError

For Node.js, the following exceptions thrown from the function are considered InputError:

• TypeError

All other exceptions thrown from the function are considered FunctionError.

To validate input in the function body:

module.exports = function(context, payload) {
    if (typeof payload !== 'string') {
        throw new TypeError("payload is not of type string");
    }

    return payload.toLowerCase();
};

Since TypeError is considered an InputError, functions should not throw it unless explicitly thrown due to an input validation error. Functions should catch and handle TypeError accordingly if it should not be classified as an InputError.