Just found interesting mod_gnutls directives , GnuTLSCache.   mod_gnutls is another alternatives to mod_ssl which provide https service to apache webserver. It is using GnuTLS instead of openssl which use by mod_ssl. The GnuTLSCache directive give us possibility to put SSL Session in memcache server on several hosts. Putting SSL session at memcache server make it accessible by several apache webservers. In other words clustering https is no hassle anymore.