Expose Pitchfork::Info.workers_count and .live_workers_count

This allow health check endpoints to consider the state of the
whole Pitchfork instance. e.g. you may want to fail the health
check if more than X% of the workers aren't live.

CHANGELOG.md

@@ -1,5 +1,6 @@
 # Unreleased
 
+- Expose `Pitchfork::Info.workers_count` and `.live_workers_count` to be consumed by application health checks.
 - Implement `before_worker_exit` callback.
 - Make each mold and worker a process group leader.
 - Get rid of `Pitchfork::PrereadInput`.

lib/pitchfork/http_server.rb

@@ -3,6 +3,7 @@
 require 'pitchfork/flock'
 require 'pitchfork/soft_timeout'
 require 'pitchfork/shared_memory'
+require 'pitchfork/info'
 
 module Pitchfork
   # This is the process manager of Pitchfork. This manages worker
@@ -165,6 +166,8 @@ def initialize(app, options = {})
       # list of signals we care about and trap in master.
       @queue_sigs = [
         :QUIT, :INT, :TERM, :USR2, :TTIN, :TTOU ]
+
+      Info.workers_count = worker_processes
       SharedMemory.preallocate_drops(worker_processes)
     end
 

lib/pitchfork/info.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+require 'pitchfork/shared_memory'
+
+module Pitchfork
+  module Info
+    class << self
+      attr_accessor :workers_count
+
+      def live_workers_count
+        now = Pitchfork.time_now(true)
+        (0...workers_count).count do |nr|
+          SharedMemory.worker_deadline(nr).value > now
+        end
+      end
+    end
+  end
+end

test/integration/info.ru

@@ -0,0 +1,10 @@
+use Rack::ContentLength
+use Rack::ContentType, "text/plain"
+run lambda { |env|
+  info = {
+    workers_count: Pitchfork::Info.workers_count,
+    live_workers_count: Pitchfork::Info.live_workers_count,
+  }
+
+  [ 200, {}, [ info.inspect ] ]
+}

test/integration/test_info.rb

@@ -0,0 +1,19 @@
+require 'integration_test_helper'
+
+class InfoTest < Pitchfork::IntegrationTest
+  def test_after_request_complete
+    addr, port = unused_port
+
+    pid = spawn_server(app: File.join(ROOT, "test/integration/info.ru"), config: <<~CONFIG)
+      listen "#{addr}:#{port}"
+      worker_processes 2
+    CONFIG
+
+    assert_healthy("http://#{addr}:#{port}")
+
+    response = http_get("http://#{addr}:#{port}/")
+    assert_equal "{:workers_count=>2, :live_workers_count=>2}", response.body
+
+    assert_clean_shutdown(pid)
+  end
+end

test/integration_test_helper.rb

@@ -150,15 +150,24 @@ def wait_healthy?(host, timeout)
     end
 
     def healthy?(url)
-      uri = URI(url)
-      http = Net::HTTP.start(uri.host, uri.port)
-      http.max_retries = 0
-      http.get("#{uri.path}?#{uri.query}")
+      http_get(url)
       true
     rescue Errno::ECONNREFUSED, Errno::EADDRNOTAVAIL, EOFError
       false
     end
 
+    def http_get(url)
+      uri = URI(url)
+      http = Net::HTTP.start(uri.host, uri.port)
+      http.max_retries = 0
+
+      path_info = uri.path.empty? ? "/" : uri.path
+      if uri.query
+        path_info = "#{path_info}?#{uri.query}"
+      end
+      http.get(path_info)
+    end
+
     def spawn_server(*args, app:, config:, lint: true)
       File.write("pitchfork.conf.rb", config)
       env = lint ? { "RACK_ENV" => "development" } : {}