apache restarted/reloaded config by itself automatically, why?

Solution 1:

cron run logrotate, logrotate reload Apache:

/var/log/apache2/*.log {
        ........
        postrotate
                if [ -f "`. /etc/apache2/envvars ; echo ${APACHE_PID_FILE:-/var/run/apache2.pid}`" ]; then
                        /etc/init.d/apache2 reload > /dev/null
                fi
        endscript
}