what to use, upstart and chkconfig

Hello,
I'm a bit new to upstart and would like to get to know it better.

Could anyone please explain to me what is the difference between starting daemons with upstart and chkconfig?

I know that services started with chkconfig at boot time would not re-spawn if killed while those started with upstart do. On the other hand I've never encountered such an issue where a service (for example sendmail) killed in the middle.

If upstart is better than chkconfig then why not using it to start all services such as network, sendmail and etc..

Your simple explaination would be appreciated.

Thanks

chkconfig is a utility to configure which services are started at boot time. Upstart is the daemon that manages how services are started and replaced System V init with CentOS 6. Upstart still supports the old SySV init scripts which are not written to take advantage of its new capabilities. The following article explains how it all works together.

http://www.openlogic.com/wazi/bid/28...s-with-Upstart