How to Create a Smart-Proxy Plugin

This guide outlines main components of a plugin, but assumes some degree of familiarity with ruby gems, bundler, rack, and Sinatra. You'll find links to useful documentation in each of the sections below.

Plugin Organization

Smart-Proxy plugins are normal ruby gems, please follow documentation at for guidance on gem creation and packaging. It is strongly recommended to follow smart_proxy_<your plugin name here> naming convention for your plugin.

We have some templates for creating your plugin:

Also, smart_proxy_pulp plugin is an example for a fully functional, yet easy to understand Smart-Proxy plugin.

Making your plugin official

Once you're ready to release the first version, please see How_to_Create_a_Plugin for info on making your plugin part of the Foreman project.

Plugin definition

A plugin definition is used to define plugin's name, version, location of rackup configuration, and other parameters. At a minimum, Plugin Descriptor must define plugin name and version. Note the base class of the descriptor is ::Proxy::Plugin:

module Proxy::Example
  class Plugin < ::Proxy::Plugin
    plugin :example, "0.0.1" 
    http_rackup_path File.expand_path("", File.expand_path("../", __FILE__))
    https_rackup_path File.expand_path("", File.expand_path("../", __FILE__))
    default_settings :hello_greeting => 'Hello there!', :important_path => '/must/exist'
    load_classes ::Proxy::Example::ClassLoader
    load_programmable_settings "::Proxy::Example::ProgrammableSettings" 
    load_dependency_injection_wirings "::Proxy::Example::DIConfiguration" 
    load_validators :my_validator => Proxy::Example::CustomValidators::MyValidator
    validate_readable :optional_path, :important_path
    validate :a_setting, :my_validator => true, :if => lambda {|settings| !settings[:a_setting].nil?}
    validate :another_setting, :my_other_validator => true
    start_services :service_a, :service_b

Here we defined a plugin called "example", with version "0.0.1", that is going to listen on both http and https ports.

Full list of descriptor parameters

Following is the full list of parameters that can be defined by the Plugin Descriptor, and the version of the Smart Proxy that they were added in.

General smart proxy configuration parameters:

  • plugin :example, "1.2.3": required. Sets plugin name to "example" and version to "0.0.1".
  • http_rackup_path "path/to/": optional, 1.6+. Sets path to http rackup configuration. If omitted, the plugin is not going to listen on the http port. Please see below for information on rackup configuration.
  • https_rackup_path "path/to/": optional, 1.6+. Sets path to https rackup configuration. If omitted, the plugin is not going to listen on the https port. Please see below for information on rackup configuration.

Loading and dependencies:

  • requires :another_plugin, '~> 1.2.0': optional, 1.6+. Specifies plugin dependencies, where ":another_plugin" is another plugin name, and '~> 1.2.0' is version specification (pls. see for details on version specification).
  • bundler_group :my_plugin_group: optional, 1.6+. Sets the name of the bundler group for plugin dependencies. If omitted the plugin name is used.
  • after_activation { do_something }: optional, 1.6+. Supplied block is going to be executed after the plugin has been loaded and enabled. Note that the block is going to be executed in the context of the Plugin Descriptor class.
  • load_classes: 1.12+. must be a class, class name, or a block. Specified class must implement "load_classes" instance method that loads module's dependencies.
  • load_dependency_injection_wirings: can be a class, class name, or a block. 1.12+. The class must implement load_dependency_injection_wirings(di_container, settings_hash) instance method.
  • start_services: 1.12+. list of dependency injection wiring labels. Services that perform work independently (asynchroniously) of http requests should implement #start method.

Settings related:

  • default_settings :first => 'my first setting', :another => 'my other setting': optional. 1.6+. Defines default values for plugin parameters. These parameters can be overridden in plugin settings file. Setting any of the parameters in default_settings to nil will trigger a validation error.
  • load_programmable_settings: can be a class, class name, or a block. 1.12+. Specified class must implement load_programmable_settings(settings_hash) instance method that returns new or updated settings.
  • load_validators: a hash of validator name (a symbol) to validator class mappings. 1.12+.
  • validate: validate :setting_one, :setting_two, ..., :setting_n, :validator_name => { :validator_param_one => 'value one', ...,}, :if => lambda {|settings| ... }, alternatively use :validator_name => true if validator has no parameters. If predicate is specified, the validator will be called only if the lambda evaluates to true. Predicate's lambda expects module's settings passed as a parameter. (1.12+)
  • validate_readable :optional_path, :important_path: optional, 1.10+. Verifies that settings listed here contain paths to files that exist and are readable. Optional settings (not listed under default_settings) will be skipped if left uninitialized.
  • validate_presence :setting_one, ..., :setting_n: optional, 1.10+. Verifies that settings listed are not equal to nil. Executed automatically for each of the default settings.

Provider definition

Some plugins are providers for an existing plugin or module in the Smart Proxy, e.g. a DNS provider.

These are registered almost identically, but use Proxy::Provider instead of Proxy::Plugin. No rackup_paths are used for providers, since they don't add any new REST API, they only add functionality to an existing module.

module Proxy::Dns::PluginTemplate
  class Plugin < ::Proxy::Provider
    plugin :dns_plugin_template, ::Proxy::Dns::PluginTemplate::VERSION

    requires :dns, '>= 1.11'

    after_activation do
      require 'smart_proxy_dns_plugin_template/dns_plugin_template_main'
      require 'smart_proxy_dns_plugin_template/dns_plugin_template_dependencies'

Additionally, each provider must specify which class implements interface expected by the main plugin. This is done by declaring an association for module's dependency injection container.

require 'dns_common/dependency_injection/dependencies'

class Proxy::Dns::DependencyInjection::Dependencies
  dependency :dns_provider, Proxy::Dns::PluginTemplate::Record

Plugin Initialization

The initialization process can be thought of as consisting of two phases: loading and validation of settings and runtime initialization -- selection of classes, their parameters, and how they will be instantiated.

During the first phase of the process, all modules are gathered into groups consisting of the main plugin and one or more providers. If any of the members of the group fail at any time during initialization, the rest of the modules in the group will be failed as well. Initialization starts with all loaded and enabled plugin (main modules) classes being collected, then for each:
  • configuration file is loaded
  • dependencies are loaded (also see load_classes)
  • configuration-related code executed, and configuration updated (also see load_runtime_configuration)
  • validators executed (also see load_validators)
  • provider names resolved to provider classes
At this point the steps above are repeated for all providers, one module group at a time. During the second phase, for each of the modules:
  • dependency injection wirings are resolved (also see load_dependency_injection_wirings)
  • services started (also see start_services)
  • module's versions are checked against other modules stated requirements (also see)

How to Load Dependencies

This technique requires Smart Proxy 1.12 or higher.

The class loader must implement load_classes instance method:

class ::Proxy::Example::ClassLoader
  def load_classes
    require 'example/class_a'
    require 'example/class_b'

alternatively, a block can be used to load dependencies:

module Proxy::Example
  class Plugin < ::Proxy::Plugin
    load_classes do
      require 'example/class_a'
      require 'example/class_b'

How to Programmatically Update Settings

This technique requires Smart Proxy 1.12 or higher.

The class must implement load_programmable_settings(settings_hash) instance method that returns new or updated settings:

class ::Proxy::Example::RuntimeConfiguration
  def load_programmable_settings(settings_hash)
    settings_hash[:a_setting] = "Hello, world" 

How to expose settings via the v2 features api.

A plugin can choose settings that can be exposed via the v2 features api:

module Proxy::Example
  class Plugin < ::Proxy::Plugin
        expose_setting :backend_url

How to expose Capabilities via the v2 features api.

A plugin can expose Capabilities that the plugin provides. These can be statically defined, or defined dynamically via a proc. The main foreman server only fetches new capabilities at Refresh time, so the intent is not have frequently changing dynamic capabilities at this time.

module Proxy::Example
  class Plugin < ::Proxy::Plugin
    # static capability
    capability :TYPE_A
    capability :TYPE_AAAA
    capability :TYPE_CNAME

    # dyanamic capability can return a single symbol/string or an array
    capability(proc{ "FOO" + "BAR" }) #a single capability 'FOOBAR'
    capability(lambda{ ["FOO", "BAR" ] }) #two capabilities 'FOO' and 'Bar'

How to Define Dependency Injection Wirings

This technique requires Smart Proxy 1.12 or higher.

The class must implement load_dependency_injection_wirings instance method that has dependency injection container and settings hash as its parameters:

class ::Proxy::Example::DIConfiguration
  def load_dependency_injection_wirings(container_instance, settings)
    container_instance.dependency :depedency_a, ::Proxy::Example::ClassA
    container_instance.dependency :dependency_b, ::Proxy::Example::ClassB
    container_instance.singleton_dependency :service_a, lambda {|container|[:example_setting], container_instance.get_dependency(:dependency_a))}

When Proxy::DependencyInjection::Container#dependency is used to define a dependency, a new instance of a class will be returned, or lambda executed every time the dependency is requested.
If only a single instance of a class is ever required, use Proxy::DependencyInjection::Container#singleton_dependency: the class will be instantiated first time the dependency is requested, and then reused on all subsequent requests.

How to Create Custom Validators

This technique requires Smart Proxy 1.12 or higher.

A validator must use ::Proxy::PluginValidators::Base as its base class and implement validate!(settings) instance method that accepts a hash containing module settings. validate! should raise an exception if the check it's making fails.

class Proxy::Example::CustomValidators
  class MyValidator < ::Proxy::PluginValidators::Base
    def validate!(settings)
      raise ::Proxy::Error::ConfigurationError("Unsupported greeting") if settings[@setting_name] != "Hello, world" 


Modular Sinatra app is used to define plugin API. Note the base class Sinatra::Base and inclusion of ::Proxy::Helpers:

module Proxy::Example
 class Api < Sinatra::Base
  helpers ::Proxy::Helpers

  get "/hello" do

Here we return a string defined in 'hello_greeting' parameter (see Plugin Descriptor above and settings file below) when a client performs a GET /hello. Please refer to Sinatra documentation on details about routing, template rendering, available helpers, etc.

Rackup Configuration

During startup Smart-Proxy assembles web applications listening on http and https ports using rackup files of enabled plugins. Plugin rackup files define mounting points of plugin API:

require 'example_plugin/example_api'

map "/example" do
  run Proxy::Example::Api

The example above should be sufficient for the majority of plugins. Please refer to Sinatra+Rack documentation for additional information.

Plugin Settings

On startup Smart-Proxy will load and parse plugin configuration files located in its settings.d/ directory. Each plugin config file is named after the plugin and is a yaml-encoded collection of key-value pairs and used to override default values of plugin parameters.

:enabled: true
:hello_greeting: "O hai!" 

This settings file enables the plugin (by default all plugins are disabled), and overrides :hello_greeting parameter. Plugin settings can be accessed through .settings method of the Plugin class, for example: ExamplePlugin.settings.hello_greeting. Global Smart-Proxy parameters are accessible through Proxy::SETTINGS, for example Proxy::SETTINGS.foreman_url returns Foreman url configured for this Smart-Proxy.

Prefer underscore naming scheme (hello_there) to camel-case (helloThere).

Bundler Configuration

Smart-Proxy relies on bundler to load its dependencies and plugins. We recommend to create a dedicated bundler config file for your plugin, and name it after the plugin. For example:

  gem 'smart_proxy_example'
  group :example do
    gem 'json'

You'll need to create a dedicated bundler group for additional dependencies of your plugin. By default the group shares the name with the plugin, but you can override it using bundler_group parameter in Plugin Descriptor. Please refer to How_to_Install_a_Smart-Proxy_Plugin for additional details on "from source" plugin installations.

Adding a DNS provider

Requires Smart Proxy 1.15 or higher (1.14 has a different interface.)

When extending the 'dns' smart proxy module, the plugin needs to create a new Proxy::Dns::Record class with do_create and do_remove methods for adding and removing of DNS records.

The easiest way to do this is using the Smart Proxy DNS plugin template which can get you up and running with a new DNS provider plugin in minutes.

DNS Provider classes are instantiated by DNS module's dependency injection container.

plugin :dns_plugin_template, ::Proxy::Dns::PluginTemplate::VERSION

And then in the main file of the plugin:

require 'dns_common/dns_common'

module Proxy::Dns::PluginTemplate
  class Record < ::Proxy::Dns::Record
    include Proxy::Log

    attr_reader :example_setting, :optional_path, :required_setting, :required_path

    def initialize(required_setting, example_setting, required_path, optional_path, dns_ttl)
      @required_setting = required_setting # never nil
      @example_setting = example_setting # can be nil
      @required_path = required_path # file exists and is readable
      @optional_path = optional_path # nil, or file exists and is readable

      # Common settings can be defined by the main plugin, it's ok to use them locally.
      # Please note that providers must not rely on settings defined by other providers or plugins they are not related to.
      super('localhost', dns_ttl)

    def do_create(name, value, type)
      # FIXME: There is no trailing dot. Your backend might require it.
      if false
        name += '.'
        value += '.' if ['PTR', 'CNAME'].include?(type)

      # FIXME: Create a record with the correct name, value and type
      raise"Failed to point #{name} to #{value} with type #{type}")

    def do_remove(name, type)
      # FIXME: There is no trailing dot. Your backend might require it.
      if false
        name += '.'

      # FIXME: Remove a record with the correct name and type
      raise"Failed to remove #{name} of type #{type}")

DNS provider support was first added in version 1.10, but the interface was updated between 1.10 and 1.11. Later in 1.15 it was further modified. Please see the history of this page for 1.14-compatible recommendations and the 1.14-stable branch of the example DNS plugin instead of master.

Adding a DHCP provider

Requires Smart Proxy 1.11 or higher.

When creating a new 'dhcp' provider smart proxy module, the plugin needs to create a new Proxy::DHCP::Server class that implements load_subnets, load_subnet_data, find_subnet, subnets, all_hosts, unused_ip, find_record, add_record, and del_record methods.

Provider classes are instantiated by DHCP module's dependency injection container.

plugin :example_dhcp_provider, ::ExampleDhcpPlugin::Provider::VERSION

And then in the main file of the plugin:

require 'dhcp_common/server'

module ::ExampleDhcpPlugin
  class Provider < ::Proxy::DHCP::Server
    include Proxy::Log
    include Proxy::Util

    def initialize

    def load_subnets
      # loads subnet data into memory

    def find_subnet(network_address)
      # returns Proxy::DHCP::Subnet that has network_address or nil if none was found

    def load_subnet_data(a_subnet)
      # loads lease- and host-records for a Proxy::DHCP::Subnet

    def subnets
      # returns all available subnets (instances of Proxy::DHCP::Subnet)

    def all_hosts(network_address)
      # returns all reservations in a subnet with network_address

    def unused_ip(network_address, mac_address, from_ip_address, to_ip_address)
      # returns first available ip address in a subnet with network_address, for a host with mac_address, in the range of ip addresses: from_ip_address, to_ip_address

    def find_record(network_address, ip_or_mac_address)
      # returns a Proxy::DHCP::Record from a subnet with network_address that has ip- or mac-address specified in ip_or_mac_address, or nil of none was found 

    def add_record(params)
      # creates a record

    def del_record(network_address,a_record)
      # removes a Proxy::DHCP::Record from a subnet with network_address

DHCP provider support was first added in version 1.11.


Make sure that your Gemfile includes the "smart-proxy" gem as a development dependency:

group :development do
  gem 'smart_proxy', :git => "" 

Ensure that your plugin has a Rakefile, for example:

require 'rake'
require 'rake/testtask'

desc 'Default: run unit tests.'
task :default => :test

desc 'Test Pulp Plugin' do |t|
  t.libs << '.'
  t.libs << 'lib'
  t.libs << 'test'
  t.test_files = FileList['test/**/*_test.rb']
  t.verbose = true

Load 'smart_proxy_for_testing' in your tests:

$: << File.join(File.dirname(__FILE__), '..', 'lib')

require 'smart_proxy_for_testing'
require 'test/unit'
require 'webmock/test_unit'
require 'mocha/test_unit'
require "rack/test" 

require 'smart_proxy_pulp_plugin/pulp_plugin'
require 'smart_proxy_pulp_plugin/pulp_api'

class PulpApiTest < Test::Unit::TestCase
  include Rack::Test::Methods

  def app

  def test_returns_pulp_status_on_200
    stub_request(:get, "#{::PulpProxy::Plugin.settings.pulp_url.to_s}/api/v2/status/").to_return(:body => "{\"api_version\":\"2\"}")
    get '/status'

    assert last_response.ok?, "Last response was not ok: #{last_response.body}" 
    assert_equal("{\"api_version\":\"2\"}", last_response.body)

To execute all tests

bundle exec rake test
. To save time during development it is possible to execute tests in a single file:
bundle exec rake test TEST=path/to/test/file

Please refer to Sinatra documention for detailed information on testing of Sinatra applications.

Once you have tests, see Jenkins for info on setting up tests under Jenkins.

Updated by Ewoud Kohl van Wijngaarden almost 5 years ago · 30 revisions