🚀 go-pugleaf

I have a server application that listens for customer queries coming in
over IP (both TCP and UDP), checks databases, and then sends back an
answer.  Occasionally there are times (like when it loses connectivity
to a remote database, or when doing admin/maintenance on a local
database) when the application needs to temporarily close those server
ports in order to force clients over to an alternate site running
another instance of the application.  Then when the situation is back to
normal, it needs to re-open the server ports.

This works fine for TCP (using a TServerSocket component and its Close
and Open methods), but now we're adding UDP access to the application,
and I've found that once the UDP socket is closed, the application can't
re-start it.  I'm using a TIdUDPServer component (from the Indy
components that came with Builder 6).  I've tried setting its Active
property false and then true again.  Setting it false works and we stop
receiving the incoming UDP packets, but then when we set it back to true
we should start seeing the incoming packets again but never do.
(Setting Active to true is in a try-catch block, but no exception is
raised.)  The only way we've found to recover the UDP server socket is
to manually shut down the whole application and then re-start it, which
is not a viable solution.

I've now tried a partial solution where instead of disabling and then
re-enabling the component, I simply set a global variable that tells the
application to temporarily ignore incoming UDP messages and not respond
to them.  This works fine for instances where the application has
explicitly shut down UDP access, but we've now found that there are some
instances (usually when we have a lot of traffic and the PC gets busy
for a while) that we seem to lose the UDP port even without having
explicitly told it to stop listening.  These instances are more
problematic.  We've already established that the application doesn't
seem to be able to re-set the UDP port, so how can I make it recover
from these cases when it stops receiving the UDP packets which are being
sent to it?  (And what's really happening here anyway?  Why does the UDP
port seem to just go away like that?)

Lesley Anne