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

Appendix D

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