The control interface of apache2 is 'apachectl'.
1. please try to copy 'apachectl' to /etc/init.d/
sudo cp /usr/local/apache2/bin/apachectl /etc/init.d/httpd (e.g. copy and rename it to httpd)
2. for ubuntu, the runlevel from 2 to 5 are the same. By default, in rc-sysinit.conf, env DEFAULT_RUNLEVEL=2.
3. for example: you can set it like below. 70 is the sequence number of Start. 80 is sequence number of Stop.
sudo update-rc.d httpd defaults 70 80
( it is equal to the command : sudo update-rc.d httpd start 70 2 3 4 5 . stop 80 0 1 6 . )
4. Use 'chkconfig' to check it
chkconfig httpd