On Sat, Jan 21, 2012 at 1:05 PM, Randy Carpenter <rcarpen@network1.net>wrote:
Several people have mentioned clustering software. Does any one have any examples of such a thing that supports v4 and v6?
Linux-HA, RSF-1, Oracle Solaris Cluster, Veritas cluster, are a few examples of clustering software.
ocf_heartbeat_anything + ocf_heartbeat_IPv6addr http://linux-ha.org/doc/man-pages/man-pages.html Obviously, building a DHCPD failover cluster involves some scripting and significant design considerations, but as far as clusters go, DNS and DHCPD failover clusters are very simple. And don't require special application support to achieve redundancy, unlike, say Firewalls, SQL, FTP, SMTP or HTTPD clusters, where a requirement may exist not to drop a single TCP connection, or fail a single query, in case of server failure. DHCPD doesn't even use TCP connections; and some amount of automatic retry by the client is a feature of the protocol. Database servers, HTTP, Firewalls, etc, are "stateful services", because there is an "in-flight" status which is not recorded in a database, and must be preserved by the application itself for graceful failover. If the Firewall connection table is not synchronized online, the failover between clustered firewalls would cause a disruption in the form of lost TCP connections, and online users will experience an immediate temporary issue at the moment of failover. The same for HTTP... a TCP connection dropping is a "permanent" error. The in-flight transactions would result in the user seeing an error page. Those are the types of applications that actually require special support or coordination from the application itself. Graceful DHCPD failover to deal with server issues can be achieved by using one of the open source or commercial clustering packages, plus a little bit of scripting. -- -JH