检查服务的可靠性

探测本身是 nslookup 命令的无限 while 循环。while 循环之前，将设置一个临时文件以放置 nslookup 回复。probefail 和 retries 变量均初始化为 0。

# Set up a temporary file for the nslookup replies.
DNSPROBEFILE=/tmp/.$RESOURCE_NAME.probe
probefail=0
retries=0

while 循环执行以下任务：

• 设置探测程序的休眠间隔

• 使用 hatimerun 启动 nslookup，传递 Probe_timeout 值并标识目标主机

• 根据 nslookup 返回码成功与否设置 probefail 变量

• 如果 probefail 设置为 1（失败），验证对 nslookup 的回复来自于数据服务样例，而不是某一其他 DNS 服务器

下面是 while 循环代码。

while :
do
   # The interval at which the probe needs to run is specified in the
   # property THOROUGH_PROBE_INTERVAL. Therefore, set the probe to sleep
   # for a duration of THOROUGH_PROBE_INTERVAL.
   sleep $PROBE_INTERVAL

   # Run an nslookup command of the IP address on which DNS is serving.
   hatimerun -t $PROBE_TIMEOUT /usr/sbin/nslookup $DNS_HOST $DNS_HOST \
   > $DNSPROBEFILE 2>&1

      retcode=$?
      if [ $retcode -ne 0 ]; then
            probefail=1
      fi

   # Make sure that the reply to nslookup comes from the HA-DNS
   # server and not from another nameserver mentioned in the 
   # /etc/resolv.conf file.
   if [ $probefail -eq 0 ]; then
# Get the name of the server that replied to the nslookup query.
   SERVER=` awk ' $1=="Server:" { print $2 }' \
   $DNSPROBEFILE | awk -F. ' { print $1 } ' `
   if [ -z "$SERVER" ]; then
      probefail=1
      else
         if [ $SERVER != $DNS_HOST ]; then
            probefail=1
         fi
   fi
fi