Ubuntu web server installed in vm is going in sleep mode often

Team,

    We have installed ubuntu 14.04 LTS on an Esxi host.Configured Apache
on this host .Its working fine ,rarely accessing web page from an client
machine
it doesnt displays the webpage.In an local host (VM) in which we have
installed
webserver its displaying the page .Checked the apache server status it says
running.
Suddenly after 15 or 30 minutes it starts working automatically.Hope is it
going on a sleep mode or something if we doesnt access the webpage for some
time.
Guys can you suggest on this ???(I am a newbie to ubuntu -Kindly bare if am
wrong)
UFW status is inactive .


Thanks,
Sundar
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