faas-js-runtime

Node.js Function Framework

This module provides a Node.js framework for executing a function that exists in a user-provided directory path as an index.js file. The directory may also contain an optional package.json file which can be used to declare runtime dependencies for the function. You can also provide a path to an arbitrary JavaScript file instead of a directory path, allowing you to execute a single file as a function.

	Project Info
License:	Apache-2.0
Issue tracker:	https://github.com/nodeshift/faas-js-runtime/issues
Engines:	Node.js >= 16

The function is loaded and then invoked for incoming HTTP requests at localhost:8080. The incoming request may be a Cloud Event or just a simple HTTP GET/POST request. The invoked user function can be async but that is not required.

The Function Interface

The function file that is loaded may export a single function or a Function object. The Function object allows developers to add lifecycle hooks for initialization and shutdown, as well as providing a way to implement custom health checks.

The Function interface is defined as:

export interface Function {
  // The initialization function, called before the server is started
  // This function is optional and should be synchronous.
  init?: () => any;

  // The shutdown function, called after the server is stopped
  // This function is optional and should be synchronous.
  shutdown?: () => any;

  // Function that returns an array of CORS origins
  // This function is optional.
  cors?: () => string[];

  // The liveness function, called to check if the server is alive
  // This function is optional and should return 200/OK if the server is alive.
  liveness?: HealthCheck;

  // The readiness function, called to check if the server is ready to accept requests
  // This function is optional and should return 200/OK if the server is ready.
  readiness?: HealthCheck;

  logLevel?: LogLevel;

  // The function to handle HTTP requests
  handle: CloudEventFunction | HTTPFunction;
}

Handle Signature

This module supports two different function signatures: HTTP or CloudEvents. In the type definitions below, we use TypeScript to express interfaces and types, but this module is usable from JavaScript as well.

HTTP Functions

The HTTP function signature is the simplest. It is invoked for every HTTP request that does not contain a CloudEvent.

interface HTTPFunction {
  (context: Context, body?: IncomingBody): HTTPFunctionReturn;
}

Where the IncomingBody is either a string, a Buffer, a JavaScript object, or undefined, depending on what was supplied in the HTTP POST message body. The HTTTPFunctionReturn type is defined as:

type HTTPFunctionReturn = Promise<StructuredReturn> | StructuredReturn | ResponseBody | void;

Where the StructuredReturn is a JavaScript object with the following properties:

interface StructuredReturn {
  statusCode?: number;
  headers?: Record<string, string>;
  body?: ResponseBody;
}

If the function returns a StructuredReturn object, then the statusCode and headers properties are used to construct the HTTP response. If the body property is present, it is used as the response body. If the function returns void or undefined, then the response body is empty.

The ResponseBody is either a string, a JavaScript object, or a Buffer. JavaScript objects will be serialized as JSON. Buffers will be sent as binary data.

CloudEvent Functions

CloudEvent functions are used in environments where the incoming HTTP request is a CloudEvent. The function signature is:

interface CloudEventFunction {
  (context: Context, event: CloudEvent): CloudEventFunctionReturn;
}

Where the return type is defined as:

type CloudEventFunctionReturn = Promise<CloudEvent> | CloudEvent | HTTPFunctionReturn;

The function return type can be anything that a simple HTTP function can return or a CloudEvent. Whatever is returned, it will be sent back to the caller as a response.

Health Checks

The Function interface also allows for the addition of a liveness and readiness function. These functions are used to implement health checks for the function. The liveness function is called to check if the function is alive. The readiness function is called to check if the function is ready to accept requests. If either of these functions return a non-200 status code, then the function is considered unhealthy.

A health check function is defined as:

/**
 * The HealthCheck interface describes a health check function,
 * including the optional path to which it should be bound.
 */
export interface HealthCheck {
  (request: Http2ServerRequest, reply: Http2ServerResponse): any;
  path?: string;
}

By default, the health checks are bound to the /health/liveness and /health/readiness paths. You can override this by setting the path property on the HealthCheck object, or by setting the LIVENESS_URL and READINESS_URL environment variables.

CLI

The easiest way to get started is to use the CLI. You can call it with the path to any JavaScript file which has a default export that is a function, or that exports a Function type. For example,

// index.js
function handle(context) {
  const event = context.cloudevent;
  // business logic
  return {
    statusCode: 200,
    statusMessage: 'OK'
  }
}

module.exports = handle;

You can expose this function as an HTTP endpoint at localhost:8080 with the CLI.

npx faas-js-runtime ./index.js

Debugging Locally

During local development, it is often necessary to set breakpoints in your code for debugging. Since functions are just javascript files, using any current debugging(VS Code, Chrome Dev Tools) method will work. The linked blog post shows how to setup and use VS Code for development debugging.

https://developers.redhat.com/articles/2021/07/13/nodejs-serverless-functions-red-hat-openshift-part-2-debugging-locally

Debugging Remotely

It is also possible to debug your function while it is running on a remote cluster. The linked blog posts shows how to setup and use the Chrome Dev Tools inspector for debugging on a cluster.

https://developers.redhat.com/articles/2021/12/08/nodejs-serverless-functions-red-hat-openshift-part-3-debugging-cluster

Functions as ES Modules

Functions can be written and imported as ES modules with either the .mjs file extension or by adding the type property to the functions package.json and setting it to module.

// index.mjs
const handle = async function(context) => { ... };

// Export the function
export { handle };

If using the type property, the package.json might look something like this:

{
  "name": "moduleName",
  "type": "module"
}

Usage as a Module

In the current working directory, there is an index.js file like this.

const { start } = require('faas-js-runtime');
const options = {
  // Pino is used as the logger implementation. Supported log levels are
  // documented at this link:
  // https://github.com/pinojs/pino/blob/master/docs/api.md#options
  logLevel: 'info'
}

// The function directory is in ./function-dir
start(require(`${__dirname}/function-dir/`), server => {
  // The server is now listening on localhost:8080
  // and the function defined in `function-dir/index.js`
  // will be invoked for each HTTP
  // request to this endpoint.
  console.log('Server listening');

  // Whenever you want to shutdown the framework
  server.close();
}, options);

In ./function-dir, there is an index.js file that looks like this.

module.exports = async function myFunction(context) {
  const ret = 'This is a test for Node.js functions. Success.';
  return new Promise((resolve, reject) => {
    setTimeout(_ => {
      context.log.info('sending response to client')
      resolve(ret);
    }, 500);
  });
};

You can use curl to POST to the endpoint:

$ curl -X POST -d 'hello=world' \
  -H'Content-type: application/x-www-form-urlencoded' http://localhost:8080

You can use curl to POST JSON data to the endpoint:

$ curl -X POST -d '{"hello": "world"}' \
  -H'Content-type: application/json' \
  http://localhost:8080

You can use curl to POST an event to the endpoint:

$ curl -X POST -d '{"hello": "world"}' \
  -H'Content-type: application/json' \
  -H'Ce-id: 1' \
  -H'Ce-source: cloud-event-example' \
  -H'Ce-type: dev.knative.example' \
  -H'Ce-specversion: 1.0' \
  http://localhost:8080

Sample

You can see this in action by running node bin/cli.js sample/index.js.