Class: Async::Container::Controller

Inherits:
Object
  • Object
show all
Defined in:
lib/async/container/controller.rb

Overview

Manages the life-cycle of one or more containers in order to support a persistent system. e.g. a web server, job server or some other long running system.

Constant Summary collapse

SIGHUP = 
Signal.list["HUP"]
SIGINT = 
Signal.list["INT"]
SIGTERM = 
Signal.list["TERM"]
SIGUSR1 = 
Signal.list["USR1"]
SIGUSR2 = 
Signal.list["USR2"]

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(notify: Notify.open!, container_class: Container, graceful_stop: true) ⇒ Controller

Initialize the controller.



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# File 'lib/async/container/controller.rb', line 26

def initialize(notify: Notify.open!, container_class: Container, graceful_stop: true)
	@notify = notify
	@container_class = container_class
	@graceful_stop = graceful_stop
	
	@container = nil
	@signals = {}
	
	self.trap(SIGHUP) do
		self.restart
	end
end

Instance Attribute Details

#container ⇒ Object (readonly)

The current container being managed by the controller.



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# File 'lib/async/container/controller.rb', line 49

def container
  @container
end

#container_class ⇒ Object (readonly)

The container class used by the controller.



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# File 'lib/async/container/controller.rb', line 43

def container_class
  @container_class
end

#graceful_stop ⇒ Object (readonly)

The graceful stop flag used by the controller.



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# File 'lib/async/container/controller.rb', line 46

def graceful_stop
  @graceful_stop
end

#notify ⇒ Object (readonly)

The notify client used by the controller.



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# File 'lib/async/container/controller.rb', line 40

def notify
  @notify
end

Instance Method Details

#create_container ⇒ Object

Create a container for the controller. Can be overridden by a sub-class.



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# File 'lib/async/container/controller.rb', line 84

def create_container
	@container_class.new(policy: self.make_policy)
end

#make_policy ⇒ Object

Create a policy for managing child lifecycle events. Can be overridden by a sub-class to provide a custom policy.



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# File 'lib/async/container/controller.rb', line 77

def make_policy
	Policy::DEFAULT
end

#reload ⇒ Object

Reload the existing container. Children instances will be reloaded using ‘SIGHUP`.



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# File 'lib/async/container/controller.rb', line 178

def reload
	@notify&.reloading!
	
	Console.info(self){"Reloading container: #{@container}..."}
	
	begin
		self.setup(@container)
	rescue
		raise SetupError, container
	end
	
	# Wait for all child processes to enter the ready state.
	Console.info(self, "Waiting for startup...")
	@container.wait_until_ready
	Console.info(self, "Finished startup.")
	
	if @container.failed?
		@notify.error!("Container failed to reload!")
		
		raise SetupError, @container
	else
		@notify&.ready!(size: @container.size, status: "Running with #{@container.size} children.")
	end
end

#restart ⇒ Object

Restart the container. A new container is created, and if successful, any old container is terminated gracefully. This is equivalent to a blue-green deployment.



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# File 'lib/async/container/controller.rb', line 126

def restart
	if @container
		@notify&.restarting!
		
		Console.info(self, "Restarting container...")
	else
		Console.info(self, "Starting container...")
	end
	
	container = self.create_container
	
	begin
		self.setup(container)
	rescue => error
		@notify&.error!(error.to_s)
		
		raise SetupError, container
	end
	
	# Wait for all child processes to enter the ready state.
	Console.info(self, "Waiting for startup...")
	container.wait_until_ready
	Console.info(self, "Finished startup.")
	
	if container.failed?
		@notify&.error!("Container failed to start!")
		
		raise SetupError, container
	end
	
	# The following swap should be atomic:
	old_container = @container
	@container = container
	container = nil
	
	if old_container
		Console.info(self, "Stopping old container...")
		old_container&.stop(@graceful_stop)
	end
	
	@notify&.ready!(size: @container.size, status: "Running with #{@container.size} children.")
rescue => error
	raise
ensure
	# If we are leaving this function with an exception, kill the container:
	if container
		Console.warn(self, "Stopping failed container...", exception: error)
		container.stop(false)
	end
end

#run ⇒ Object

Enter the controller run loop, trapping ‘SIGINT` and `SIGTERM`.



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# File 'lib/async/container/controller.rb', line 204

def run
	@notify&.status!("Initializing controller...")
	
	with_signal_handlers do
		self.start
		
		while @container&.running?
			begin
				@container.wait
			rescue SignalException => exception
				if handler = @signals[exception.signo]
					begin
						handler.call
					rescue SetupError => error
						Console.error(self, error)
					end
				else
					raise
				end
			end
		end
	end
rescue Interrupt
	self.stop
rescue Terminate
	self.stop(false)
ensure
	self.stop(false)
end

#running? ⇒ Boolean

Whether the controller has a running container.

Returns:

  • (Boolean) 


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# File 'lib/async/container/controller.rb', line 90

def running?
	!!@container
end

#setup(container) ⇒ Object

Spawn container instances into the given container. Should be overridden by a sub-class.



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# File 'lib/async/container/controller.rb', line 102

def setup(container)
	# Don't do this, otherwise calling super is risky for sub-classes:
	# raise NotImplementedError, "Container setup is must be implemented in derived class!"
end

#start ⇒ Object

Start the container unless it’s already running.



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# File 'lib/async/container/controller.rb', line 108

def start
	unless @container
		Console.info(self, "Controller starting...")
		self.restart
	end
	
	Console.info(self, "Controller started.")
end

#state_string ⇒ Object

The state of the controller.



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# File 'lib/async/container/controller.rb', line 53

def state_string
	if running?
		"running"
	else
		"stopped"
	end
end

#stop(graceful = @graceful_stop) ⇒ Object

Stop the container if it’s running.



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# File 'lib/async/container/controller.rb', line 119

def stop(graceful = @graceful_stop)
	@container&.stop(graceful)
	@container = nil
end

#to_s ⇒ Object

A human readable representation of the controller.



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# File 'lib/async/container/controller.rb', line 63

def to_s
	"#{self.class} #{state_string}"
end

#trap(signal, &block) ⇒ Object

Trap the specified signal.



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# File 'lib/async/container/controller.rb', line 70

def trap(signal, &block)
	@signals[signal] = block
end

#wait ⇒ Object

Wait for the underlying container to start.



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# File 'lib/async/container/controller.rb', line 95

def wait
	@container&.wait
end