Log-Based Readiness Notification for Kubernetes Probes in async-container

lib/async/container/notify.rb

@@ -6,6 +6,7 @@
 require_relative "notify/pipe"
 require_relative "notify/socket"
 require_relative "notify/console"
+require_relative "notify/log"
 
 module Async
 	module Container
@@ -18,6 +19,7 @@ def self.open!
 				@client ||= (
 					Pipe.open! ||
 					Socket.open! ||
+					Log.open! ||
 					Console.open!
 				)
 			end

lib/async/container/notify/log.rb

@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+# Released under the MIT License.
+# Copyright, 2020-2024, by Samuel Williams.
+
+require_relative "client"
+require "socket"
+
+module Async
+	module Container
+		module Notify
+			class Log < Client
+				# The name of the environment variable which contains the path to the notification socket.
+				NOTIFY_LOG = "NOTIFY_LOG"
+
+				# Open a notification client attached to the current {NOTIFY_LOG} if possible.
+				def self.open!(environment = ENV)
+					if path = environment.delete(NOTIFY_LOG)
+						self.new(path)
+					end
+				end
+
+				# Initialize the notification client.
+				# @parameter path [String] The path to the UNIX socket used for sending messages to the process manager.
+				def initialize(path)
+					@path = path
+				end
+
+				# @attribute [String] The path to the UNIX socket used for sending messages to the controller.
+				attr :path
+
+				# Send the given message.
+				# @parameter message [Hash]
+				def send(**message)
+					data = JSON.dump(message)
+
+					File.open(@path, "a") do |file|
+						file.puts(data)
+					end
+				end
+
+				# Send the specified error.
+				# `sd_notify` requires an `errno` key, which defaults to `-1` to indicate a generic error.
+				def error!(text, **message)
+					message[:errno] ||= -1
+
+					super
+				end
+			end
+		end
+	end
+end

lib/async/container/notify/server.rb

@@ -5,6 +5,7 @@
 # Copyright, 2020, by Olle Jonsson.
 
 require "tmpdir"
+require "socket"
 require "securerandom"
 
 module Async

test/async/container/notify/log.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+# Released under the MIT License.
+# Copyright, 2020-2025, by Samuel Williams.
+# Copyright, 2020, by Olle Jonsson.
+
+require "async/container/controller"
+require "async/container/controllers"
+
+require "tmpdir"
+
+describe Async::Container::Notify::Pipe do
+	let(:notify_script) {Async::Container::Controllers.path_for("notify")}
+	let(:notify_log) {File.expand_path("notify-#{::Process.pid}-#{SecureRandom.hex(8)}.log", Dir.tmpdir)}
+
+	it "receives notification of child status" do
+		system({"NOTIFY_LOG" => notify_log}, "bundle", "exec", notify_script)
+
+		lines = File.readlines(notify_log).map{|line| JSON.parse(line)}
+
+		expect(lines.last).to be == {"ready" => true}
+	end
+end