set cron job to run at random time between midnight and 4am

Dockerfile

@@ -96,9 +96,6 @@ ADD files/server.xml conf/server.xml
 
 ADD files/bin/setenv.sh /opt/tier/setenv.sh
 RUN chmod +x /opt/tier/setenv.sh
-ADD files/tier-crontab /opt/tier/tier-crontab
-RUN crontab /opt/tier/tier-crontab
-ADD files/tier-crontab /etc/cron.d/tier-crontab
 ADD files/bin/startup.sh /usr/bin/startup.sh
 RUN chmod +x /usr/bin/startup.sh
 ADD files/bin/sendtierbeacon.sh /usr/bin/sendtierbeacon.sh

files/bin/startup.sh

@@ -1,5 +1,21 @@
-#!/bin/sh
+#!/bin/bash
+#set env vars for cron job
 /opt/tier/setenv.sh
+
+#build crontab file with random start time between midnight and 3:59am
+echo "#send daily beacon to TIER Central" > /opt/tier/tier-cron
+echo "* * * * * /usr/bin/sendtierbeacon.sh >> /var/log/cron.log 2>&1" >> /opt/tier/tier-cron
+echo "#"$(expr $RANDOM % 59) $(expr $RANDOM % 3) "* * * /usr/bin/sendtierbeacon.sh >> /var/log/cron.log 2>&1" >> /opt/tier/tier-cron
+chmod 644 /opt/tier/tier-cron
+
+#install crontab
+crontab /opt/tier/tier-crontab
+
+#create cron logfile
 touch /var/log/cron.log
+
+#start crond
 /usr/sbin/crond
+
+#start tomcat
 /usr/local/tomcat/bin/catalina.sh run