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Tuning the LifeKeeper Heartbeat

Overview of the Tunable Heartbeat

The LifeKeeper heartbeat is the signal sent between LifeKeeper servers over the communications path(s) to ensure each server is "alive". There are two aspects of the heartbeat that determine how quickly LifeKeeper detects a failure:

The heartbeat values are specified by two tunables in the LifeKeeper defaults file /etc/default/LifeKeeper. These tunables can be changed if you wish LifeKeeper to detect a server failure sooner than it would using the default values:

The following table summarizes the defaults and minimum values for the tunables over both TCP and TTY heartbeats. The interval for a TTY communications path cannot be set below 2 seconds because of the slower nature of the medium.

Tunable

Default Value

Minimum Value

LCMHBEATTIME

5

1 (TCP) 2 (TTY)

LCMNUMHBEATS

3

2 (TCP or TTY)

Important Note: The values for both tunables MUST be the SAME on all servers in the cluster.

Example

Consider a LifeKeeper cluster in which both intervals are set to the default values. LifeKeeper sends a heartbeat between servers every 5 seconds.  If a communications problem causes the heartbeat to skip two beats, but it resumes on third heartbeat, LifeKeeper takes no action. However, if the communications path remains dead for 3 beats, LifeKeeper will label that communications path as dead, but will initiate a failover only if the redundant communications path is also dead.

Configuring the Heartbeat

You must manually edit file /etc/default/LifeKeeper to add the tunable and its associated value. Normally, the defaults file contains no entry  for these tunables; you simply append the following lines with the desired value as follows:

LCMHBEATTIME=x

LCMNUMHBEATS=y

If you assign the value to a number below the minimum value, LifeKeeper will ignore that value and use the minimum value instead.

Configuration Considerations

Note: If you are using both TTY and TCP communications paths, the value for each tunable applies to both communications paths. The only exception is if the interval value is below 2, which is the minimum for a TTY communications path.

For example, suppose you specify the lowest values allowed by LifeKeeper in order to detect failure as quickly as possible:

LCMHBEATTIME=1

LCMNUMHBEATS=2

LifeKeeper will use a 1 second interval for the TCP communications path, and a 2 second interval for TTY. In the case of a server failure, LifeKeeper will detect the TCP failure first because its interval is shorter (2 heartbeats that are 1 second apart), but then will do nothing until it detects the TTY failure, which will be after 2 heartbeats that are 2 seconds apart.

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