Heart beat in service guard cluster

[sokolova]

whathappens if heart beat fails?
is there any impact for runnng cluster?

[Jose Mosquera]

Hi,

Serviceguard nodes monitor each other to be sure they can all communicate and cooperate. Every node in a Serviceguard cluster sends heartbeat messages over the network and listens for heartbeat messages from other nodes. Heartbeat messages are sent at regular intervals, defined in the cluster
configuration file as the HEARTBEAT_INTERVAL.
If a node does not receive a heartbeat from another node, it begins the process of re-forming the cluster and removing the unreachable node from cluster membership. Figure 1 shows the steps in a failover caused by a failed node.

http://h20338.www2.hp.com/enterprise/downloads/Optimizing%20failover_6-22.pdf

Rgds.

[P Arumugavel]

To say in simple words,

If hertbeat fails, each node will think the other node fails. so each node will reform the cluster, which is not expected. This is called split brain syndrome.

Yes. It is surely impact the cluster normal behavior. But this Split-Brain Syndrome is prevented by Cluster Quorum.

Read the "Managing Serviceguard Cluster" to get the full information.

Rgds...

[sokolova]

Thank you understand now

[Sajjad Sahir]

Dear friend

There is NODE_TIMEOUT VALUE in the cluster configuration file, if node B is not getting heartbeat message from node A until NODE_TIMEOUT VALUE specified in the cluster then node B will consider node A is failed then service guard will reform the cluster without the failed node A)

thanks and regards

Sajjad Sahir

[Emil Velez]

heartbeat should not fail since you have a standby lan card.. or you have a heartbeat on multiple subnets.

[nijokj]

HEARTBEAT_IP

IP notation indicating a subnet that will carry the cluster heartbeat.

A heartbeat IP address must be an IPv4 address.


Heartbeat configuration requirements:

A minimum Serviceguard configuration on HP-UX 11i v2 or 11i v3 needs two network interface cards for the heartbeat in all cases, using one of the following configurations:

Two heartbeat subnets; or

One heartbeat subnet with a standby; or

One heartbeat subnet using APA with two physical ports in hot standby mode or LAN monitor mode.


Or you can configured heartbeat using cross-over cables between nodes.

One more way is through serial communication.




If heartbeat is failed between nodes ,which will cause split brain syndrome.

suppose we have communication lost between the four servers in your cluster and suppose they are able to communicate in pair of two and not all. Suppose a,b,c,d are four nodes and during the failure a can talk to b and c to d in that case both nodes will try to form two seperate cluster of two nodes each. This situation is called a split brain syndrome where more than one clusters can be created within one cluster. which will cause correction of data which will not be expected.

To avoid this situation we have quorum server, which will be contacted during the above scenarion and which two nodes contacts the quorum server first will continue to operate in cluster and other nodes will be shutdown thus avoiding split brain syndrome. This is also termed as tie breaker mechanism.

In a two node cluster, the same can be achived by a lock disk itself.