crontab 定时执行docker exec命令

• 监控docker及docker内程序的运行情况，可以用crontab来实现。在宿主机上设置定时执行任务（每分钟执行一次）：

$ crontab -e
# m h  dom mon dow   command
*/1 * * * * bash /root/check-detect.sh

• 脚本 check-detect.sh：

#!/bin/bash -xv

default_containername=detect1.0
default_homepath=$(dirname $(realpath $0))

containername=$1
if [ "$containername" == "" ]; then containername=${default_containername}; fi
imagename=${containername}:latest

homepath=$2
if [ "$homepath" == "" ]; then homepath=${default_homepath}; fi


logd=${homepath}/log
mkdir -p ${logd}/

logfile=${logd}/log.$(basename $0).$(date +%Y%m%d)
#exec >> ${logfile}

#echo "${logfile} &> /dev/null
#exec 2> ${logfile}

dump() {
  echo "$(date +'%Y-%m-%d %H:%M:%S') [log]: $1" >> ${logfile}
}

ERROR_EXIT(){
  dump $1
  exit 1
}


# start
dump "${HOSTNAME} $(basename $0) start $(date +%Y%m%d%H%M%S) pid:$$"

# check docker
dump "check docker"
if [ `systemctl status docker |grep Active |grep inactive |wc -l` -gt 0 ]; then
  dump "starting docker"
  systemctl start docker
  dump "docker started"
  sleep 5
fi

# check docker container
dump "check exists ${containername}"
if [ `docker ps -a |grep ${containername} |wc -l` -lt 1 ]; then
  dump "begin to run docker container: ${containername}"
  docker run -itd --name ${containername} --privileged=true \
    -v ${homepath}/data:/data \
    --restart always \
    -p 80:80 \
    ${imagename} /usr/sbin/init
  [ $? -ne 0 ] && ERROR_EXIT
  dump "${containername} running"
fi
dump "check running ${containername}"
if [ `docker ps |grep ${containername} |wc -l` -lt 1 ]; then
  dump "starting ${containername}"
  docker start ${containername}
  [ $? -ne 0 ] && ERROR_EXIT
  dump "${containername} started"
fi

dump "docker exec -it ${containername} bash -c \"bash /quick-start.sh\""
docker exec -it ${containername} bash -c "bash /quick-start.sh"
[ $? -ne 0 ] && ERROR_EXIT "docker-exec-${containername}-error"

# end
dump "${HOSTNAME} $(basename $0) end $(date +%Y%m%d%H%M%S)"

exit 0

设置好后，监控log，发现 docker exec 时总是失败，最后百度+谷歌，找到了原因：
http://www.89cool.com/821.html
Your docker exec command says it needs "pseudo terminal and runs in interactive mode" (-it flags) while cron doesn't attach to any TTYs.
大致意思 exec 加了 -it 参数就开启了一个终端，计划任务是无法进入任何终端的。

把 docker exec 的参数 -it 去掉后问题解决了。

---

docker exec -it 参数详解：
https://docs.docker.com/engine/reference/commandline/exec/

--interactive , -i		Keep STDIN open even if not attached
--tty , -t		Allocate a pseudo-TTY

关于tty：
https://www.howtogeek.com/428174/what-is-a-tty-on-linux-and-how-to-use-the-tty-command/