A part of Failover
, Failsh is a Tcl application that monitors services on remote hosts as specified in the Tcl script fed to it. If no master host can provide the service, and no slave provides it, failsh will start the service on the local host and notify the other hosts through the failover state daemon faild(l).
Currently at version 0.5.22, released 2009-06-05
The availability of many network application servers could easily be improved if a second server would automatically take over in case of a failure. This is e. g. the case with webservers, DNS servers, directories or network information systems like NIS or LDAP.
Some OSs provide high-availability features that can be used to implement failover, but in most cases, only a commercial add-on can solve the problem.
This package of failover utilites is designed to solve this problem in some cases. It consists of a daemon that collects state information about services so that other systems can find out about the services on a given host. The daemon is polled at regular intervals in time by a failover shell, which then decides whether a service needs to be started on the local machine or not. This shell is programmable in Tcl and can call (of course) external programs.