shync/Readme.md

Simple parallel server cluster management tool using ssh and scp

# shync

Simple parallel server cluster management tool for Node using ssh and scp. Specify an ssh or scp command and it will run on all servers in the cluster in parallel.

## Installation

    npm install shync

## ssh

```js
var Shync = require('shync').Shync;

var cluster = new Shync({
  domains: ['23.42.103.164',
            'mydomain.com'],
  user:    'ubuntu',
  keyLoc:  '/path/to/public/key',
  bypassFingerprint: true
});

cluster.run('node ~/stuff/important.js', function(err){
  if (err) return console.log(err);
  console.log('you\'ve done something important on many machines!');
});
```

## scp

```js
cluster.run('~/important.tar.gz', '~/stuff/important.tar.gz', function(err){
  if (err) return console.log(err);
  console.log('you\'ve done something important on many machines!');
});
```

## Chaining commands

```js
cluster.run('~/important.tar.gz', '~/stuff/important.tar.gz', function(err){
  if (err) return console.log(err);
    cluster.run('tar xzvf ~/stuff/important.tar.gz', function(err){
      if (err) return console.log(err);
        cluster.run('node ~/stuff/important.js', function(err){
          if (err) return console.log(err);
            console.log('you\'ve done something important on many machines!');
          }
        });
      }
    });
  }
});
```

## Return codes and the err callback parameter

If a command was not successful, shync callbacks will receive the [return code](http://en.wikipedia.org/wiki/Exit_status) of the command that was run as the `err` paramater. shync treats the success of a command as "all or nothing." If the command was successful on all remote machines, `null` is returned to the callback. If even one machine returned a non 0 code, then the command as a whole is deemed to have failed and the non 0 code will be returned as the err param to the callback.

shync fails quickly if a remote machine returns a non 0 code. All outstanding connections to the remaining servers are severed, since their return codes are irrelevant now that a non 0 code has been received.

## stdout and stderr

You can specify a function to be called with the stdout and/or stderr of the program you're running:

```js

function stdout(out) {
  console.log(out);
}

function stderr(err) {
  console.log(err);
}

var cluster = new Shync({
  ...
  stdout: stdout,
  stderr: stderr
});

cluster.run('rm -rf /', cb);
// ec2-54-226-122-165.compute-1.amazonaws.com:STDERR: rm: it is dangerous to operate recursively on `/'
// ec2-54-226-122-165.compute-1.amazonaws.com:STDERR: rm: use --no-preserve-root to override this failsafe

cluster.run('ls -a ~', cb);
// ec2-54-226-122-165.compute-1.amazonaws.com:STDOUT: .  ..  .bash_history  .bashrc  .ssh
```

## bypassFingerprint

```js
var cluster = new Shync({
  ...
  bypassFingerprint: true
  ...
});
```

You know when you ssh from the command line into a brand new box, and you get this message:

    $ ssh user@example.com
    The authenticity of host 'example.com (23.20.102.179)' can't be established.
    RSA key fingerprint is 2f:5d:69:26:e2:a0:23:53:f7:0a:21:51:0a:74:8a:49.
    Are you sure you want to continue connecting (yes/no)?

bypassFingerprint: true stops this from happening.

_Warning_ Use bypassFingerprint at your own risk.