Plugin System

StarCluster has support for user contributed plugins. Plugins allow developers to further configure the cluster in addition to the default cluster configuration provided by StarCluster. Plugins are used to provide custom cluster configurations for a variety of computing needs.

Creating a New Plugin

A StarCluster plugin is simply a Python class that extends starcluster.clustersetup.ClusterSetup and implements a run method. This class must live in a module that is on the PYTHONPATH. By default, StarCluster will add the ~/.starcluster/plugins directory to the PYTHONPATH automatically.

Below is a very simple example of a StarCluster plugin that installs a package on each node using apt-get after the cluster has been configured:

from starcluster.clustersetup import ClusterSetup

class PackageInstaller(ClusterSetup):
     def __init__(self, pkg_to_install):
          self.pkg_to_install = pkg_to_install
     def run(self, nodes, master, user, user_shell, volumes):
          for node in nodes:
               node.ssh.execute('apt-get -y install %s' % self.pkg_to_install)

For this example we assume that this class lives in a module file called ubuntu.py and that this file lives in the ~/.starcluster/plugins directory.

This is a very simple example that simply demonstrates how to execute a command on each node in the cluster. For a more sophisticated example, have a look at StarCluster’s default setup class starcluster.clustersetup.DefaultClusterSetup. This is the class used to perform StarCluster’s default setup routines. The DefaultClusterSetup class should provide you with a more complete example of the plugin API and the types of things you can do with the arguments passed to a plugin’s run method.

Using the Logging System

When writing plugins it’s better to use StarCluster’s logging system rather than print statements in your code. This is because the logging system handles formatting messages and writing them to the StarCluster debug file. Here’s a modified version of the PackageInstaller plugin above that uses the logging system:

from starcluster.clustersetup import ClusterSetup
from starcluster.logger import log

class PackageInstaller(ClusterSetup):
     def __init__(self, pkg_to_install):
          self.pkg_to_install = pkg_to_install
          log.debug('pkg_to_install = %s' % pkg_to_install)
     def run(self, nodes, master, user, user_shell, volumes):
          for node in nodes:
               log.info("Installing %s on %s" % (self.pkg_to_install, node.alias))
               node.ssh.execute('apt-get -y install %s' % self.pkg_to_install)

The first thing you’ll notice is that we’ve added an additional import statement to the code. This line imports the log object that you’ll use to log messages. In the plugin’s constructor we’ve added a log.debug() call that shows the current value of the pkg_to_install variable. All messages logged with the log.debug() method will always be printed to the debug file, however, these messages will only be printed to the screen if the user passes the –debug flag to the starcluster command.

In the plugin’s run method, we’ve added a log.info() call to notify the user that the package they specified in the config is being installed on a particular node. All messages logged with the log.info() method will always be printed to the screen and also go into the debug file. In addition to log.info() and log.debug() there are also log.warn(), log.critical(), log.fatal(), and log.error() methods for logging messages of varying severity.

Adding Your Plugin to the Config

To use a plugin we must first add it to the config and then add the plugin’s config to a cluster template. Below is an example config for the example plugin above:

[plugin pkginstaller]
setup_class = ubuntu.PackageInstaller
pkg_to_install = htop

In this example, pkg_to_install is an argument to the plugin’s constructor (ie __init__). A plugin can, of course, define multiple constructor arguments and you can configure these arguments in the config similar to pkg_to_install in the above example.

After you’ve defined a [plugin] section, you can now use this plugin in a cluster template by configuring its plugins setting:

[cluster smallcluster]
....
plugins = pkginstaller

This setting instructs StarCluster to run the pkginstaller plugin after StarCluster’s default setup routines. If you want to use more than one plugin in a template you can do so by providing a list of plugins:

[cluster smallcluster]
....
plugins = pkginstaller, myplugin

In the example above, starcluster would first run the pkginstaller plugin and then the myplugin plugin afterwards. In short, order matters when defining plugins to use in a cluster template.

Using the Development Shell

To launch StarCluster’s development shell, use the shell command:

$ starcluster shell
StarCluster - (http://star.mit.edu/cluster)
Software Tools for Academics and Researchers (STAR)
Please submit bug reports to starcluster@mit.edu

>>> Importing module config
>>> Importing module plugins
>>> Importing module cli
>>> Importing module awsutils
>>> Importing module ssh
>>> Importing module utils
>>> Importing module static
>>> Importing module exception
>>> Importing module cluster
>>> Importing module node
>>> Importing module clustersetup
>>> Importing module image
>>> Importing module volume
>>> Importing module tests
>>> Importing module templates
>>> Importing module optcomplete
>>> Importing module boto
>>> Importing module ssh

[~]|1>

This launches you into an IPython shell with all of the StarCluster modules automatically loaded. You’ll also notice that you have the following variables available to you automagically:

1. cm - manager object for clusters (starcluster.cluster.ClusterManager)
2. cfg - object for retrieving values from the config file (starcluster.config.StarClusterConfig)
3. ec2 - object for interacting with EC2 (starcluster.awsutils.EasyEC2)
4. s3 - object for interacting with S3 (starcluster.awsutils.EasyS3)

Plugin Development Workflow

The process of developing and testing a plugin generally goes something like this:

1. Start a small test cluster (2-3 nodes):

   $ starcluster start testcluster -s 2

2. Install and configure the additional software/settings by hand and note the steps involved:

   $ starcluster sshmaster testcluster
   root@master $ apt-get install myapp
   ...

3. Write a first draft of your plugin that attempts to do these steps programmatically

4. Add your plugin to the StarCluster configuration file

5. Test your plugin on your small test cluster using the runplugin command:

   $ starcluster runplugin myplugin testcluster

   Alternatively, you can also run your plugin using the development shell (requires IPython):

   $ starcluster shell
   [~]> cm.run_plugin('myplugin', 'testcluster')

6. Fix any coding errors in order to get the plugin to run from start to finish using the runplugin command.

7. Login to the master node and verify that the plugin was successful:

   $ starcluster sshmaster testcluster