chef/cookbooks/poise-service

Poise-Service Cookbook

A Chef cookbook to provide a unified interface for services.

What is poise-service?

Poise-service is a tool for developers of "library cookbooks" to define a service without forcing the end-user of the library to adhere to their choice of service management framework. The poise_service resource represents an abstract service to be run, which can then be customized by node attributes and the poise_service_options resource. This is a technique called dependency injection, and allows a measure of decoupling between the library and application cookbooks.

Why would I use poise-service?

Poise-service is most useful for authors of library-style cookbooks, for example the apache2, mysql, or application cookbooks. When using other service management options with Chef, the author of the library cookbook has to add specific code for each service management framework they want to support, often resulting in a cookbook only supporting the favorite framework of the author or depending on distribution packages for their init scripts. The poise_service resource allows library cookbook authors a way to write generic code for all service management frameworks while still allowing users of that cookbook to choose which service management framework best fits their needs.

How is this different from the built-in service resource?

Chef includes a service resource which allows interacting with certain service management frameworks such as SysV, Upstart, and systemd. poise-service goes further in that it actually generates the configuration files needed for the requested service management framework, as well as offering a dependency injection system for application cookbooks to customize which framework is used.

What service management frameworks are supported?

• SysV (aka /etc/init.d)
• Upstart
• systemd
• Inittab
• Runit
• Monit
• Solaris
• AIX
• Supervisor (coming soon!)

Quick Start

To create a service user and a service to run Apache2:

poise_service_user 'www-data'

poise_service 'apache2' do
  command '/usr/sbin/apache2 -f /etc/apache2/apache2.conf -DFOREGROUND'
  stop_signal 'WINCH'
  reload_signal 'USR1'
end

or for a hypothetical Rails web application:

poise_service_user 'myapp'

poise_service 'myapp-web' do
  command 'bundle exec unicorn -p 8080'
  user 'myapp'
  directory '/srv/myapp'
  environment RAILS_ENV: 'production'
end

Resources

poise_service

The poise_service resource is the abstract definition of a service.

poise_service 'myapp' do
  command 'myapp --serve'
  environment RAILS_ENV: 'production'
end

Actions

• :enable – Create, enable and start the service. (default)
• :disable – Stop, disable, and destroy the service.
• :start – Start the service.
• :stop – Stop the service.
• :restart – Stop and then start the service.
• :reload – Send the configured reload signal to the service.

Attributes

• service_name – Name of the service. (name attribute)
• command – Command to run for the service. This command must stay in the foreground and not daemonize itself. (required)
• user – User to run the service as. See poise_service_user for any easy way to create service users. (default: root)
• directory – Working directory for the service. (default: home directory for user, or / if not found)
• environment – Environment variables for the service.
• stop_signal – Signal to use to stop the service. Some systems will fall back to SIGKILL if this signal fails to stop the process. (default: TERM)
• reload_signal – Signal to use to reload the service. (default: HUP)
• restart_on_update – If true, the service will be restarted if the service definition or configuration changes. If 'immediately', the notification will happen in immediate mode. (default: true)

Service Options

The poise-service library offers an additional way to pass configuration information to the final service called "options". Options are key/value pairs that are passed down to the service provider and can be used to control how it creates and manages the service. These can be set in the poise_service resource using the options method, in node attributes or via the poise_service_options resource. The options from all sources are merged together in to a single hash.

When setting options in the resource you can either set them for all providers:

poise_service 'myapp' do
  command 'myapp --serve'
  options status_port: 8000
end

or for a single provider:

poise_service 'myapp' do
  command 'myapp --serve'
  options :systemd, after_target: 'network'
end

Setting via node attributes is generally how an end-user or application cookbook will set options to customize services in the library cookbooks they are using. You can set options for all services or for a single service, by service name or by resource name:

# Global, for all services.
override['poise-service']['options']['after_target'] = 'network'
# Single service.
override['poise-service']['myapp']['template'] = 'myapp.erb'

The poise_service_options resource is also available to set node attributes for a specific service in a DSL-friendly way:

poise_service_options 'myapp' do
  template 'myapp.erb'
  restart_on_update false
end

Unlike resource attributes, service options can be different for each provider. Not all providers support the same options so make sure to check the documentation for each provider to see what options are available.

poise_service_options

The poise_service_options resource allows setting per-service options in a DSL-friendly way. See the Service Options section for more information about service options overall.

poise_service_options 'myapp' do
  template 'myapp.erb'
  restart_on_update false
end

Actions

• :run – Apply the service options. (default)

Attributes

• resource – Name of the service. (name attribute)
• for_provider – Provider to set options for.

All other attribute keys will be used as options data.

poise_service_user

The poise_service_user resource is an easy way to create service users. It is not required to use poise_service, it is only a helper.

poise_service_user 'myapp' do
  home '/srv/myapp'
end

Actions

• :create – Create the user and group. (default)
• :remove – Remove the user and group.

Attributes

• user – Name of the user. (name attribute)
• group – Name of the group. Set to false to disable group creation. (name attribute)
• uid – UID of the user. (default: automatic)
• gid – GID of the group. (default: automatic)
• home – Home directory of the user.
• shell – Shell of the user. (default: /bin/nologin if present or /bin/false)

Providers

sysvinit

The sysvinit provider supports SystemV-style init systems on Debian-family and RHEL-family platforms. It will create the /etc/init.d/<service_name> script and enable/disable the service using the platform-specific service resource.

poise_service 'myapp' do
  provider :sysvinit
  command 'myapp --serve'
end

By default a PID file will be created in /var/run/service_name.pid. You can use the pid_file option detailed below to override this and rely on your process creating a PID file in the given path.

Options

• pid_file – Path to PID file that the service command will create.
• pid_file_external – If true, assume the service will create the PID file itself. (default: true if pid_file option is set)
• template – Override the default script template. If you want to use a template in a different cookbook use 'cookbook:template'.
• command – Override the service command.
• directory – Override the service directory.
• environment – Override the service environment variables.
• reload_signal – Override the service reload signal.
• stop_signal – Override the service stop signal.
• user – Override the service user.
• never_restart – Never try to restart the service.
• never_reload – Never try to reload the service.
• script_path – Override the path to the generated service script.

upstart

The upstart provider supports Upstart. It will create the /etc/init/service_name.conf configuration.

poise_service 'myapp' do
  provider :upstart
  command 'myapp --serve'
end

As a wide variety of versions of Upstart are in use in various Linux distributions, the provider does its best to identify which features are available and provide shims as appropriate. Most of these should be invisible however Upstart older than 1.10 does not support setting a reload signal so only SIGHUP can be used. You can set a reload_shim option to enable an internal implementaion of reloading to be used for signals other than SIGHUP, however as this is implemented inside Chef code, running initctl reload would still result in SIGHUP being sent. For this reason, the feature is disabled by default and will throw an error if a reload signal other than SIGHUP is used.

Options

• reload_shim – Enable the reload signal shim. See above for a warning about this feature.
• template – Override the default configuration template. If you want to use a template in a different cookbook use 'cookbook:template'.
• command – Override the service command.
• directory – Override the service directory.
• environment – Override the service environment variables.
• reload_signal – Override the service reload signal.
• stop_signal – Override the service stop signal.
• user – Override the service user.
• never_restart – Never try to restart the service.
• never_reload – Never try to reload the service.

systemd

The systemd provider supports systemd. It will create the /etc/systemd/system/service_name.service configuration.

poise_service 'myapp' do
  provider :systemd
  command 'myapp --serve'
end

Options

• template – Override the default configuration template. If you want to use a template in a different cookbook use 'cookbook:template'.
• command – Override the service command.
• directory – Override the service directory.
• environment – Override the service environment variables.
• reload_signal – Override the service reload signal.
• stop_signal – Override the service stop signal.
• user – Override the service user.
• never_restart – Never try to restart the service.
• never_reload – Never try to reload the service.
• auto_reload – Run systemctl daemon-reload after changes to the unit file. (default: true)
• restart_mode – Restart mode for the generated service unit. (default: on-failure)

inittab

The inittab provider supports managing services via /etc/inittab using SystemV Init. This can provide basic process supervision even on very old *nix machines.

poise_service 'myapp' do
  provider :inittab
  command 'myapp --serve'
end

NOTE: Inittab does not allow stopping services, and they are started as soon as they are enabled.

Options

• never_restart – Never try to restart the service.
• never_reload – Never try to reload the service.
• pid_file – Path to PID file that the service command will create.
• service_id – Unique 1-4 character tag for the service. Defaults to an auto-generated hash based on the service name. If these collide, bad things happen. Don't do that.

ServiceMixin

For the common case of a resource (LWRP or plain Ruby) that roughly maps to "some config files and a service" poise-service provides a mixin module, PoiseService::ServiceMixin. This mixin adds the standard service actions (enable, disable, start, stop, restart, and reload) with basic implementations that call those actions on a poise_service resource for you. You customize the service by defining a service_options method on your provider class:

def service_options(service)
  # service is the PoiseService::Resource object instance.
  service.command "/usr/sbin/#{new_resource.name} -f /etc/#{new_resource.name}/conf/httpd.conf -DFOREGROUND"
  service.stop_signal 'WINCH'
  service.reload_signal 'USR1'
end

You will generally want to override the enable action to install things related to the service like packages, users and configuration files:

def action_enable
  notifying_block do
    package 'apache2'
    poise_service_user 'www-data'
    template "/etc/#{new_resource.name}/conf/httpd.conf" do
      # ...
    end
  end
  # This super call will run the normal service enable,
  # creating the service and starting it.
  super
end

See the poise_service_test_mixin resource and provider for examples of using ServiceMixin in an LWRP.

Sponsors

Development sponsored by Bloomberg.

The Poise test server infrastructure is sponsored by Rackspace.

License

Copyright 2015-2016, Noah Kantrowitz

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.