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distributed shell job control with role based configuration for Node.js
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README.md

Poly.shell

- distributed shell job control with role based configuration for Node.js

This package has been renamed poly.shell, so use require('poly.shell'). The poly name has been handed over to another project that use the term cross platform. Documentation does NOT reflect this.

This package is no longer actively maintained, but was fairly complete at the time. Nodejs, however, have evolved and may have broken parts. Today Grunt and grunt-ssh fills some of the space this package was intended for.

Original text

Poly.shell is primarily intended to administer server clusters, but it can also be used to schedule other kinds of distributed computation, or to just run simple shell commands.

Typical scenarios are to install new software, to monitor log files, to upload new versions of web sites, and to verify that backup jobs have been completing successfully.

The Capistrano and Vlad tools for Ruby on Rails are designed for these kind of jobs. Poly.shell is a lower level tool but forms a good foundation for performing standard routines such as deploying a new version of a web site pulled from the latest source control branch.

The basic idea is to define a set of named jobs with actions that can run in sequence, in parallel, or some variation thereof, on multiple local and remote sites using role names to aid configuration.

Poly.shell can also be used as a convenient way to quickly run system local shell commands:

require('poly').shell().run("touch IWasHere");

or to run commands on a single remote system:

require('poly').shell('example.com').run("ls");

Poly.shell can also run multiple jobs in different roles:

poly = require('poly');
jobs = poly.jobs();
sites = jobs.sites;

sites.add('my-local-site', ['role-x', 'role-y']);
sites.add('my-remote-site-1', 'role-x', { host: 'app1.example.com' });
sites.add('my-remote-site-2', ['role-x', 'role-y'], { host: 'app2.example.com' });

jobs.add('job-a', 'role-x', function() {
  this.shell.run("echo hello > " + this.site.name + ".flag", this.async());
  var x = this.shared.visited || [];
  x.push(this.site.name);
  this.shared.visited = x;
});

jobs.add('job-b', 'role-y', function() {
  //...
});

jobs.run(['job-a', 'job-b'], function() {
  console.log "all jobs done";
  console.log this.shared.visited;
});

Here we created 3 different local and remote sites where jobs can run. We use the shell to access the remote systems and the role names to decide which jobs to run where.

Because the same job runs on multiple sites there are different ways to synchronise. The default is to start the first job in parallel on all matching sites and each site will go on to the next job as soon as its current job invocation is complete, like a relay race.

There are different run schedules (parallel, atomic, ...), and jobs.run can be restricted to only run jobs on sites with certain roles. Whenever a site does not have a role that match the next job, the site will skip that job and immediately proceed with the next job listed.

Resources

Repository:

https://github.com/dvidelabs/poly.shell

Online Documentation:

http://dvidelabs.github.com/poly.shell/

Installation

To install latest public release with npm:

npm install -g poly

Or download or clone from github to some user local folder. Enter folder and install using npm:

npm install

Or globally with npm 1.0.0:

npm install -g

Test that things are ok (see warning below):

make test

Note, the following tests run on a remote system example.com that is supposed to be configured .ssh/config to match a suitable server.

*Don't use this on production systems!!! *

make rtest

Tests normally dump files in a local tmp dir that is cleaned with make clean. Remote tests are not cleaned up, please inspect the test files in the rtest folder.

CoffeeScript

Poly.shell is written primarily in CoffeeScript, but that shouldn't change anything. If, for some reason (including debugging), a JavaScript version is needed, a JavaScript only module can be created in sub-folder using:

make js

Passwords

Poly.shell does not support ssh password based account login. It is assumed that ssh will use ssh keys without passwords, or with passwords managed by an external agent such as ssh-agent.

Poly.shell does, however, support sudo password prompts after ssh login. In the basic form a shell detects a sudo prompt and issues a silent prompt to the user console.

Since many processes may target the same site, and many sites may have the same admin password, it is convenient to cache a password across sites.

This works by creating a password cache object that is stored in all site configurations that are supposed to share a sudo passwords.

Shells can detect when another shell is prompting for a password and wait for the user to enter the password, and otherwise start a password prompt when no valid password is cached.

Scheduling

The Poly.shell job control scheduler is fairly simple. A schedule is an array of job names which can be run in one the following modes: sequential, atomic, parallel, or the default: site-sequential where different jobs may run at the same time but each site will only see one of the jobs at a time. These schedules can then be chained to more complex scenarios if needed, and the same jobs can be reused in different schedules. This model is somewhat similar to the various Node.js async libraries like seq, flow and async, but with role based job distribution, reporting, configuration, unique identifiers, (remote) shell support, and password agents.

Poly.shell has no dependency resolver, but it is possible to use Poly.shell inside a Jakefile, or in similar tools, or even in a web framework like Express.

Locking primitives can be added, for example by using Node.js EventEmitter objects in the shared context, or in site configurations for example. The password cache and agent does something similar. Locking provides a good algorithm for scheduling transactions.

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