HP-UX SNAplus2 NOF Programmer's Guide

Introduction to the NOF API
Client-Server Operation
Chapter 162
configuration file is copied to backup servers (either when they are
started or when the master copy is changed) so that all backup servers
hold a copy of the latest information.
If the master server fails or if the SNA software on that computer is
stopped, a backup server takes over as the master. The domain
configuration file on this server is used as the master copy and is copied
to other servers as necessary. When the master server is restarted, it
receives a copy of the domain configuration from the backup server
currently acting as master and then takes over as the master.
In general, define at least one backup server in addition to the master
server. Any remaining servers can be defined as additional backup
master servers or they can be left as peer servers. A peer server obtains
configuration information from the master server as required but cannot
act as a backup server.
If at any time the master server and all backup servers are inactive, a
node on a peer server can still operate, and you can still change the
node’s configuration. However, you cannot access the domain
configuration file and therefore cannot access the configuration of
domain resources (as opposed to node resources). This means that you
will not be able to start the 3270 emulation program or RJE programsor
allocate CPI-C conversations using symbolic destination names defined
in the configuration file.
There is one situation in which SNAplus2 cannot maintain a consistent
configuration of domain resources across the LAN; it is your
responsibility to maintain the configuration in this case. This situation
occurs when the LAN is split by a network failure into two
noncommunicating domains, each containing one or more backup
servers. In this situation, there will be an acting master server in each
domain, which will hold any changes made to the domain configuration
file in that domain but will be unaware of any changes made in the other
domain. When the LAN connection is re-established, the domain
configuration file from the original master server (or from the highest
backup server available in either of the two domains if the master is
inactive at this point) will become the domain configuration file across
the LAN; this will overwrite any changes made to the domain
configuration file in the other domain while the network was split.
Because of this, do not attempt to make any changes to the domain
configuration file in either of the two domains while the LAN connection
is broken. Changes can be made to the configuration of individual nodes.