Hi Dave,
First of all, the application "handle" represents a network (domain socket,
actually) connection to the SA. Any attempt to communicate using that handle
while the SA is down will return a network-level error to the application.
It can then do whatever failover is needed in a domain-specific manner.
Secondly, applications are responsible for re-registering their service with
the SA on a regular interval defined by the application. The SLPReg call has
a usLifetime argument that represents a number of seconds (less than or
equal to SLP_LIFETIME_MAXIMUM). The registration expires in the SA after
usLifetime seconds has passed since SLPReg was called.
Often, this number is something like 300 seconds, so about every 5 minutes
the application should call SLPReg again. This means that a registration
will never be down for more than 5 minutes. If the service is
mission-critical, it would be prudent to specify a shorter lifetime value
and re-register more often, but it would seem, in light of the nature of
advertised network services, that once a minute is sufficient, even for
mission-critical applications.
Regards,
John
From: mclellan, dave [mailto:[email protected]]
Sent: Wednesday, September 11, 2013 7:17 AM
To: [email protected]
Subject: [Openslp-users] How does an application know to re-register?
Hi all. Novice question alert; we are fairly new to use of OpenSLP.
Suppose an application has registered using SLPReg successfully in an
environment without the Directory agent. If the local Service Agent fails
for whatever reason and must be restarted, all registrations held by that
Service Agent are lost.
How does the application get notified, if at all, that it should close its
handle, open a handle and register again? Is there any notification
provided via the registration callback? I don't think so, from what I have
read. My conclusion is that there isn't a way for a registered process to
know if the openSLP infrastructure on which it depends fails and has been
re-initialized.
Such notification would have to be done by some other monitoring entity,
presumably the same entity which notices the SLP infrastructure failure and
recovers it. Are these correct assumptions?
Thanks very much for any advice.
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Dave McLellan, VMAX Software Engineering, EMC Corporation, 176 South St.
Mail Stop 176-V1 1/P-36, Hopkinton, MA 01749
Office: 508-249-1257, Mobile: 978-500-2546, [email protected]
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