I just noticed that the problem is related to log rotation. Always happens near 6:30AM. Apache stops after log rotation and does not restart.
Error.log:
Quote:[Wed Aug 27 06:33:34 2008] [notice] SIGUSR1 received. Doing graceful restart
[Wed Aug 27 06:33:34 2008] [notice] FastCGI: wrapper mechanism enabled (wrapper: /usr/lib/apache2/suexec)
[Wed Aug 27 06:33:34 2008] [notice] FastCGI: process manager initialized (pid 10839)
[Wed Aug 27 06:33:34 2008] [notice] Apache/2.2.8 (Ubuntu) mod_fastcgi/2.4.6 configured -- resuming normal operations
[Wed Aug 27 06:33:34 2008] [warn] FastCGI: server "/var/www/fcgi/master/php5-fcgi-starter" (uid 2000, gid 2000) started (pid 10840)
[Wed Aug 27 06:33:34 2008] [notice] caught SIGWINCH, shutting down gracefully