批量监测dns是否可用脚本，不可用时并切换

#!/usr/bin/env python
# coding=utf-8
# hexm@2016-02-14

import time
import requests
import paramiko
import subprocess
import requests

HOST = (
        "10.88.2.182:22",
　　　　 "10.88.2.183:22",
 　　　　"10.88.2.184:22"
)

class DnsHelper(object):

    def checkStatus(self, dns):
        '''
        检查状态
        '''
        status = subprocess.call('/usr/bin/dig www.baidu.com @%s +time=1 &> /dev/null' % dns, shell=True)
        return status

    def modifyStatus(self):
        NS = "nameserver %s
nameserver %s
nameserver %s" % (DNS[0], DNS[1], DNS[2])
        cmd = "echo "%s" > /etc/resolv.conf" % NS
        self.exec_command(cmd)

    def exec_command(self, cmd):
        '''
        远程连接修改

        '''
        private_key = paramiko.RSAKey.from_private_key_file('/root/.ssh/id_rsa')
        ssh = paramiko.SSHClient()
        ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
        for host in HOST:
            h,p = host.strip().split(':')
            try:
                ssh.connect(hostname=h, port=int(p), username='root', pkey=private_key, timeout=1)
                stdin, stdout, stderr = ssh.exec_command(cmd)
            except:
                continue
            ssh.close()
        self.alarm("切换dns为%s成功" % DNS[0])

    def alarm(self, info):
        url = "http://alarm.mingxiao.com/alarm/index.php?type=13&gid=199&msg=%s" % info 
        try:
            r = requests.get(url)
        except:
            pass

if __name__ == "__main__":
    TAG = 0  # 标志位，0正常，其他不正常
    DNS = ["202.106.0.20", "119.29.29.29", "223.5.5.5"]

    obj = DnsHelper()
    while True:
        for i in range(2):  # 两次次状态是否为0， 0正常，其他不正常
            status = obj.checkStatus(DNS[0])
        print(status,TAG,DNS)
            if status != 0:
                TAG += 1
            time.sleep(10) 
        if TAG != 0:  # 检测一次不正常，切换dns
            TAG = 0
            obj.alarm('DNS %s 检测不正常,正在切换' % DNS[0])
            DNS.append(DNS[0])  
            DNS.remove(DNS[0])  # 不正常的DNS放到末尾，
            status = obj.checkStatus(DNS[0])  # 检查新DNS是否正常
            if status == 0:  # 正常则切换dns
                obj.modifyStatus()
                #TAG = 0
    time.sleep(300)