The Cranker Router

Daniel Flower's crank4j is a reverse proxy which provides implicit discovery behaviour.

This is a server which implements a cranker router.

Install

To install from npm:

npm install cranker-router

Start a router

Start from npm package:

cranker-router --help

to start, specify a port for the router:

cranker-router 8090

you can also specify a port for the cranker:

cranker-router 8090 20000

You can also install globally and run:

npm install -g cranker-router
cranker-router 8090 20000

Embedding in JS

There's no default server, so you have to embed it.

Start a cranker on port 8090:

const crankerRouter = require("./server.js");

async function start() {
  const routerObject = await crankerRouter(8090);
  return routerObject;
}

start().then();

Start a cranker, with the router on any old port, which is really good for testing:

const crankerRouter = require("./server.js");

async function start() {
  const routerObject = await crankerRouter(0);
  const routerPort = routerObject.getListener().address().port;
  console.log("router started on", routerPort);
  return routerObject;
}

start().then();

What about if you need to know the port of the cranker websocket?

const crankerRouter = require("./server.js");

async function start() {
  const routerObject = await crankerRouter(8090);
  const crankerPort = routerObject.getCrankerListener().address().port;
  console.log("cranker started on", crankerPort);
  return routerObject;
}

start().then();

Want information about what has been connected?

const crankerRouter = require("./server.js");

async function start() {
  const routerObject = await crankerRouter(0);
  const crankerRoutes = routerObject.getCrankedRoutes();
  console.log("paths routed", crankerRoutes.getCrankedRoutes());
  return routerObject;
}

start().then();

Do you want a cranker router with some other routes pre-defined?

const crankerRouter = require("./server.js");

async function start() {
  const routerObject = await crankerRouter(0);
  routerObject.get("/cranker/status", function (req, res) {
     res.send("<h1>just a test!</h1>");
  });
  return routerObject;
}

start().then();

In this situation a connector connecting with the route /cranker/status won't work because the router object's mapping will take precedence.

These routes follow the express routing rules, the documentation for which can be found here.

Lastly, how would you start and stop it?

const crankerRouter = require("./server.js");

async function start() {
  const routerObject = await crankerRouter(0);
  return routerObject;
}

start().then(router => router.close(););

Performance trade offs and configuration

If a cranker connector websocket is not available to route an incomming request then cranker router has to wait for the connector to establish a socket.

The router option waitOnCrankerTimeout specifies the number of miliseconds it waits. The defaut is 8,000 milliseconds, which is 8 seconds.

If it takes longer than 8 seconds to receive a cranker connector socket then cranker router returns a 504 to the requesting user agent.

This is an acceptable default in the situation when a connector has been configured to make 2 websocket connections to the cranker router.

If you need a definitively lower response time, even if that might result in more 504 error responses, then reduce the waitOnCrankerTimeout, for example, like this:

const crankerRouter = require("cranker-router");
async function start() {
  const routerObject = await crankerRouter(0, {
     waitOnCrankerTimeout: 2000
  });
  return routerObject;
}

crankit for developement

I maintain a separate project called crankit which is a developer tool to allow you to start a router and then connect node js projects to it with a command line.

See crankit for more details.