如何使用monit监控nginx乘客

Question

我有几个由nginx passenger部署的rails应用程序。我希望使用monit来监控这些应用程序。如何使用monit监控这些应用程序？我也应该监控nginx吗？

Answer 1

这就是我解决这个问题的方法。首先，我给application.rb添加了：

# Monit support
if defined?(PhusionPassenger)
  require 'pidfile_manager'
  PhusionPassenger.on_event(:starting_worker_process) do |forked|
    if forked
      # We're in smart spawning mode.
      PidfileManager.write_pid_file
    else
      # We're in conservative spawning mode. We don't need to do anything.
    end
  end

  PhusionPassenger.on_event(:stopping_worker_process) do
    PidfileManager.remove_pid_file
  end
end

然后我实现了PidfileManager：

module PidfileManager
  extend self

  BASENAME = '/var/tmp/rack.*.pid'

  def write_pid_file
    pid = Process.pid
    count = 1
    pidfile = nil
    go_over_pid_files do |file, saved_pid|
      file_id = file[/(\d+)/,1].to_i
      # Increase counter only if we met the same file id
      count += 1 if file_id == count
      # We're already there
      return if saved_pid == pid
      # Check if the process is alive
      res = begin
        Process.kill(0, saved_pid)
      rescue Errno::ESRCH
        nil
      end
      # It's dead, reuse
      unless res
        pidfile = file
        break
      end
    end
    pidfile ||= BASENAME.sub('*', count.to_s)
    File.open(pidfile, 'w') {|f| f.write(pid.to_s)}
  end

  def remove_pid_file
    pid = Process.pid
    go_over_pid_files do |file, saved_pid|
      if pid == saved_pid
        File.unlink(file)
        break
      end
    end
  end

  private
  def go_over_pid_files
    Dir[BASENAME].each do |file|
      saved_pid = File.read(file).to_i
      yield file, saved_pid
    end
  end

end

然后告诉monit使用/var/tmp/rack.X.pid作为pidfile来监视每个实例。

Answer 2

不确定现在发布这篇文章是否太晚了，但这就是我如何使用monit (5.14)来阻止passenger rails应用程序消耗太多内存的方法：

monit：

check program ourapp_live with path     "/usr/local/bin/check_passenger_mem_usage ourapp 500" as "ourappuser"
 if status != 0 then alert
 if status != 0 then restart
 start program = "/bin/touch /var/www/vhosts/ourapp/railsapp/current/tmp/restart.txt"
 stop program = "/bin/true"

外壳脚本monit调用(check_passenger_mem_usage)：

#!/bin/bash
#
#
USER=$1
TRIGGER=$2

if [ -z $USER ] || [ -z $TRIGGER ]
then
    echo "missing args"
    echo "usage:"
    echo "         check_passenger_mem_usage username alert_threshold"
    echo
    echo "(alert_threshold is in mb)"
    echo
    exit 1
fi

MAX=`/usr/local/rvm/gems/ruby-1.8.7-p357/wrappers/passenger-memory-stats | grep $USER | awk '{print $2}' | sort -n | tail -1|cut -d. -f1`

if [ "$MAX" -gt $TRIGGER ]
then
    echo
    echo "${USER}: We got a runaway! Gobbling ${MAX} mb"
    echo
    exit 1
else
    echo
    echo "Max is ${MAX}"
    exit 0
fi

可能不是最好的解决方案，因为它重新启动了整个rails应用程序，但至少它防止了rails消耗大量的内存，如果应用程序时不时地占用一点内存。

Answer 3

如果您希望让它们保持运行，并在出现错误时让它们重新启动，那么您可能更好地查看supervisord。supervisord实际上是自己运行进程，而不是通过轮询来查看进程是否正在运行。它运行的守护进程需要运行前台才能工作，但它非常有效，并且会比monit更快地启动服务(monit通常每分钟轮询一次，而supervisord会看到进程结束并立即重新启动)。

我们在生产中使用supervisord来运行我们所有的守护进程(nginx，beanstalkd，memcached，各种python服务等)，然后使用monit来监控supervisord作为一个添加的备份。