Frequent Out of Memory issue

Hi community

we have a website with mostly static content and scrolling pictures. There is no database for this website.
The webserver crashes frequently with "out of memory".

This issue resolves, after I reboot the node, until the next time this occurs

I found very little useful information on var/log/messages.
Is there some other log that I can use to identify the root cause.

note: this is related to https://www.linode.com/community/questions/27533/website-not-available.
I apologize to create a new issue, but I thought this will get more attention