Crow.Plugin behaviour (crow v0.2.1)

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The behaviour all configured plugins should implement.

Overview

Writing Munin plugins is rather simple. A trivial plugin with the default Munin node setup is a script with two main behaviours:

  • When invoked with the command line argument config, print out configuration of the plugin, such as graph setup (title, category, labels), field information and more. A full description of all options can be found at the Plugin reference documentation.

  • When not invoked with any command line argument, print out the values for fields declared in the config command.

This is the foundation from which plugins are developed. Since our node runs in the BEAM, we've taken a different approach here. Instead of being executable shell scripts, crow plugins are modules which provide three functions:

  • name/1, which returns the name of the plugin shown to Munin. This must be unique amongst all plugins configured on the node.

  • config/1, which returns the configuration of the plugin, corresponding to the first invocation form described above.

  • values/1, which returns the values of the plugin, corresponding to the second invocation form described above.

These take a single argument, namely the plugin options as specified in the crow settings, see options/0. If your plugin has no configuration options, it is safe to ignore this value. Instead of printing to standard output, these return a list of charlists which is then sent to the peer via TCP.

Community plugins

Plugins for the crow node can be found in the crow_plugins repository.

Summary

Types

options()

Options passed to the plugin, generally per configuration in Crow.

Callbacks

config(options)

Display the configuration for this plugin.

name(options)

Return the name of the plugin displayed to peers.

values(options)

Display values for this plugin.

Types

options()

(since 0.2.0) 
@type options() :: Keyword.t()

Options passed to the plugin, generally per configuration in Crow.

If no options were passed, this will be an empty list.

Callbacks

config(options)

@callback config(options()) :: [charlist()]

Display the configuration for this plugin.

Each element in the output represents a single line in the output. Adding newlines to each line is done by the worker.

For reference, see Munin plugin config command from the official documentation.

Example

def config(_opts) do
  [
    'graph_title Total processes',
    'graph_category BEAM',
    'graph_vlabel processes',
    'processes.label processes'
  ]
end

name(options)

@callback name(options()) :: charlist()

Return the name of the plugin displayed to peers.

Example

def name(_opts) do
  'my_plugin'
end

values(options)

@callback values(options()) :: [charlist()]

Display values for this plugin.

Example

def values(_opts) do
  [
    'processes.value #{length(:erlang.processes())}'
  ]
end