If the switchover from active to standby is "commanded" then there is
the opportunity to "tell" the applications on the server to close their
connections - either explicitly with some sort of defined interface, or
implicitly by killing the processes. Then the IP can be brought-up on
the standby and processes started/enabled/whatever and the clients can
establish their new connections. The ioctl here (at least if it is like
the tcp_discon options in HP-UX/Solaris) wouldn't be any better than
just killing the process in so far as what happens on the network - in
fact, it could be worse since the RST will not be retransmitted if lost,
but FINs would. So, the ioctl could still leave clients twisting in the
ether waiting for their application-level heartbeats to kick-in anyway.
Heck, depending on their heartbeat lengths, even the FIN stuff if lost
could leave them depending on their heartbeats.
If the switchover from active to standby is "uncommanded" it probably
means the primary went belly-up which means you don't have the
opportunity to make an ioctl call anyway, and you are back to the
heartbeats.
rick jones
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