Make health probe server more general purpose

lib/good_job.rb

@@ -30,8 +30,10 @@
 require "good_job/multi_scheduler"
 require "good_job/notifier"
 require "good_job/poller"
+require "good_job/middleware/catch_all"
+require "good_job/middleware/healthcheck"
 require "good_job/http_server"
-require "good_job/probe_server"
+require "good_job/utility_server"
 require "good_job/scheduler"
 require "good_job/shared_executor"
 require "good_job/systemd_service"

lib/good_job/cli.rb

@@ -101,8 +101,10 @@ def start
       capsule.start
       systemd.start
 
-      if configuration.probe_port
-        probe_server = GoodJob::ProbeServer.new(port: configuration.probe_port)
+      middleware = Rails.application.config.good_job.middleware
+      port = Rails.application.config.good_job.middleware_port
+      if middleware && port
+        probe_server = GoodJob::UtilityServer.new(app: middleware, port: port)
         probe_server.start
       end
 

lib/good_job/middleware/catch_all.rb

@@ -0,0 +1,9 @@
+module GoodJob
+  module Middleware
+    class CatchAll
+      def self.call(env)
+        [404, {}, ["Not found"]]
+      end
+    end
+  end
+end

lib/good_job/middleware/healthcheck.rb

@@ -0,0 +1,25 @@
+module GoodJob
+  module Middleware
+    class Healthcheck
+      def initialize(app)
+        @app = app
+      end
+
+      def call(env)
+        case Rack::Request.new(env).path
+        when '/', '/status'
+          [200, {}, ["OK"]]
+        when '/status/started'
+          started = GoodJob::Scheduler.instances.any? && GoodJob::Scheduler.instances.all?(&:running?)
+          started ? [200, {}, ["Started"]] : [503, {}, ["Not started"]]
+        when '/status/connected'
+          connected = GoodJob::Scheduler.instances.any? && GoodJob::Scheduler.instances.all?(&:running?) &&
+                      GoodJob::Notifier.instances.any? && GoodJob::Notifier.instances.all?(&:listening?)
+          connected ? [200, {}, ["Connected"]] : [503, {}, ["Not connected"]]
+        else
+          @app.call(env)
+        end
+      end
+    end
+  end
+end

lib/good_job/utility_server.rb

@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+module GoodJob
+  class UtilityServer
+    def self.task_observer(time, output, thread_error) # rubocop:disable Lint/UnusedMethodArgument
+      return if thread_error.is_a? Concurrent::CancelledOperationError
+
+      GoodJob._on_thread_error(thread_error) if thread_error
+    end
+
+    def initialize(app:, port:)
+      @port = port
+      @app = app
+    end
+
+    def start
+      @handler = HttpServer.new(@app, port: @port, logger: GoodJob.logger)
+      @future = Concurrent::Future.new { @handler.run }
+      @future.add_observer(self.class, :task_observer)
+      @future.execute
+    end
+
+    def running?
+      @handler&.running?
+    end
+
+    def stop
+      @handler&.stop
+      @future&.value # wait for Future to exit
+    end
+  end
+end