HP HP-UX SNAplus2, Administration Manual

Page: 377 / 398

Appendix D 377
Using SNAplus2 in a High Availability Environment
Using SNAplus2 with MC/ServiceGuard
the SNAplus2 software. Insert this command in the
customer_defined_halt_cmds
section of the Package Control Script
as follows:
function customer_defined_halt_cmds
{
snap stop
}
After ServiceGuard stops the SNAplus2 package on the primary server,
it will attempt to start the package on the backup server. Using our
example, it might seem simple to just add the following command to
start the
HALS
LS on the backup server:
snapadmin start_ls, ls_name=HALS
But this command will fail if any of the following are true:
• The SNAplus2 control daemon is not running on the backup server.
The SNAplus2 control daemon must always be running in order to
activate a n LS .
• The SNAplus2 port
HAPORT
is not running on the backup server.
In addition, you must make sure the following requirements are
satisfied:
• The remote SNA system does not restrict which HP 9000 server can
activate the same PU configuration. For example, the remote SNA
system allows communication from any MAC address in a Token Ring
LAN. This requirement is necessary to ensure that the backup server
will be allowed to activate the same LS that the primary server used.
• The primary server and the backup server both have a compatible I/O
configuration. This is an important requirement that will be further
explained in the section “I/O Compatibility Constraints”.
• The backup server is not running SNAplus2 when ServiceGuard
attempts to migrate the package. If the backup server is running
SNAplus2 , then the third command (
snapadmin init_node
) will
fail. The reason is that SNAplus2 only allows one node to run on a
server.
With this in mind, you might be tempted to issue the command
snap
stop
as the first run command. However, there are certain failure
conditions where this command is not sufficient. If the primary server
panics or loses all networking capability, it will be unable to send a
message to other SNAplus2 servers that indicates the node has
stopped on the primary server. In this case, SNAplus2 will refuse to