[Zope-dev] web sites are keep crashing

Hi All, We have hosted 3 websites in a single web server with 4GB RAM. All the three sites were built using zope. Almost every day the sites are crashing with 504-proxy error. The sites are up when i restart the httpd and zope. Why this happens all the time? Your help on fixing this issue is greatly appreciated. Thanks and regards, Babylakshmi