What is the difference between a machine name and a host name.

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2020-09-22 13:36

Every machine in an RSF cluster needs a unique and unchanging machine name for RSF-1 to associate with it. This is normally the same as host name, but must be different if the host name is to be changed as part of a service fail over (or the host name doesn't resolve to a valid IP address).

The machine names used by RSF-1 are the names which appears in MACHINE lines in the config file. These names are normally associated with real machines by checking to see that they match the host name of that machine. However if a host ID appears on a MACHINE line, then the host name check is not done, and the association is made by checking the host ID (as returned by hac_hostid) instead. Note that in this case the IP address of the machine MUST be specified on the end of the line, as it is assumed that the machine name is not the same as the host name, and thus can't be used to look up the IP address of the host.

This flexible naming scheme also allows multiple hosts in a cluster to have the same host name (a requirement seen in a few applications).

To specify the optional host ID of the machine on the MACHINE line preceded it by "0x" (to indicate it is a hexadecimal value). RSF-1 will then identify that machine by the name on the MACHINE line, even if it does not match the real host name. Here is an example MACHINE entry with corresponding host ID:

MACHINE slug 0x2ae5747

RSF also sets the environment variable RSF_MACHINE_NAME in any service startup/shutdown scripts to the machine name in use. This allows scripts to create log messages using the same machine name as rsfmon itself.

Machine names are also used on heartbeat (NETDISK and SERIAL) lines to indicate what machine the heartbeat is being sent to, and on SERVER lines to indicate which machines may act as act as a server for a service.

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