cat app/cron
# check status every 10 min
*/10 * * * * root /root/app/check.sh

cat app/start_app.sh
#!/usr/bin/env bash

# Start crond
/usr/sbin/crond
status=$?
if [ $status -ne 0 ]; then
  echo "Failed to start crond: $status"
  exit $status
fi

# Start your app
start_your_app
status=$?
if [ $status -ne 0 ]; then
  echo "Failed to start app: $status"
  exit $status
fi

# Naive check runs checks once a minute to see if either of the processes exited.
# This illustrates part of the heavy lifting you need to do if you want to run
# more than one service in a container. The container exits with an error
# if it detects that either of the processes has exited.
# Otherwise it loops forever, waking up every 60 seconds

while sleep 60; do
  ps aux |grep crond |grep -q -v grep
  PROCESS_1_STATUS=$?
  ps aux |grep your_app |grep -q -v grep
  PROCESS_2_STATUS=$?
  # If the greps above find anything, they exit with 0 status
  # If they are not both 0, then something is wrong
  if [ $PROCESS_1_STATUS -ne 0 -o $PROCESS_2_STATUS -ne 0 ]; then
    echo "One of the processes has already exited."
    exit 1
  fi

FROM centos:7
COPY . /app
RUN yum install cronie -y
RUN cp /app/cron /var/spool/cron/root
CMD ./app/start_app.sh