role

Develop services as single processes, deploy them as multiple - from a single code base.

Each service is a role and exports a stream, as every good networker does. Then cluster / distributed roles as you wish.

Network partitions / reconnects are handled transparently.

Example: Subscribe to role

Let's write a CLI app that uppercases stdin. Because in production we'll want to use multiple processes and especially split up uppercasing from the frontend, we use a role for each:

var role = require('role');
var through = require('through');

role('uppercaser', function () {
  return through(function (chunk) {
    this.queue(chunk.toString().toUpperCase());
  });
});

role('main', function () {
  role.subscribe('uppercaser', function (upper) {
    process.stdin
      .pipe(through(function (c) { this.queue(c.toString()) }))
      .pipe(upper)
      .pipe(process.stdout);
  });
});

main is a special role which will always be executed immediately. All the other rules will be executed when requested via role.get().

Now, to start as a single process:

$ node example/uppercaser.js
hi
HI
what's up
WHAT'S UP

To start as two seperate processes, one being the uppercaser (read: doing something cpu intensive), the other being being the frontend:

$ HUB=7888 ROLE=main node example/uppercaser.js 
$ CLIENT=7888 ROLE=uppercaser node example/uppercaser.js 

To start as three seperate processes:

$ HUB=7888 ROLE=main node example/uppercaser.js 
$ CLIENT=7888 ROLE=uppercaser node example/uppercaser.js 
$ CLIENT=7888 ROLE=uppercaser node example/uppercaser.js 
$ # you can kill any client without causing downtime

When using distributed / production mode just make sure that there's always at least one hub running.

Example: Get role

When you only need a stream once, role.get(name) returns a stream that you can use immediately and buffers if necessary:

var role = require('..');
var through = require('through');

role('uppercaser', function () {
  return through(function (chunk) {
    this.queue(chunk.toString().toUpperCase());
  });
});

role('main', function () {
  process.stdin.setEncoding('utf8');
  process.stdin
    .pipe(role.get('uppercaser'))
    .pipe(process.stdout);
});

API

role(name, fn)

Set fn to be role name. fn should return a Stream or a Function that returns a Stream.

role.get(name)

Return a Stream that can be used immediately and if necessary buffers until the connection is made.

role.subscribe(name, fn)

Call fn with a stream for role name. When the connection is lost and a new one is made or already available, call fn again.

Env flags

Pass none for local mode. Pass HUB and ROLE or CLIENT and ROLE for distributed/production mode.

• HUB: Be a hub and listen on that port.
• CLIENT: Be a client and listen on that port.
• ROLE: The role to serve. Multiple roles are activated when you pass a comma-seperated list, like main,db.

Debugging

Pass DEBUG=role to see what's going on:

Installation

With npm do

$ npm install role

License

Copyright (c) 2013 Julian Gruber <julian@juliangruber.com>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.