What is the role of Corosync ?
Ans: It is one of the important component of pacemaker, used for handling the communication between cluster nodes, apart from this pacemaker also uses it to check cluster membership and quorum data.
Q:2 What is the use of Quorum in Red Hat Clustering?
Ans:  A Healthy cluster requires quorum to operate, if any case cluster lose the quorum then cluster will stop or terminate resources and resources group to maintain the data integrity.
So quorum can be defined as voting system which is required to maintain the cluster integrity. In a cluster each node or member has one vote, depending on the number of nodes in cluster, cluster will form the quorum when either half or more than half votes are present.
Q:3 What are the different type of fencing supported by Red Hat cluster?
Ans: Red Hat Cluster support two type of fencing,
a)       Power Fencing
b)      Storage or Fabric Fencing
Q:4: How to open ports in firewall for Cluster communication?
Ans: Let’s assume you have two node cluster, then run the following command on each node to open the firewall ports related to Red Hat clustering,
~]# firewall-cmd --permanent --add-service=high-availability
~] # firewall-cmd --reload
Q: 5 What is use of pcs command?
Ans: pcs is command line utility, used to configure and manage cluster nodes. In other terms we can say pcs mange every aspect of Pacemaker cluster.
Q: 6 How to check your Cluster status?
Ans: Cluster status be displayed by using two commands,
~]# pcs cluster status
~]# pcs status
Q:7 How to enable automatic startup of cluster on all the configured cluster nodes?
Ans: Let’s assume you have three node cluster and want to start the cluster services and join the cluster automatically after reboot. So to achieve run the below command from any of the cluster node,
~]# pcs cluster enable --all
Q:8 How to prohibit a cluster node from hosting the services?
Ans: There are some situations where admin need to temporarily suspend a cluster node without affecting the cluster operation, this can be easily achieved by marking that cluster node as “standby“,
Run the below command from one cluster node,
~]# pcs cluster standby {Cluster_Node_Name}
To Resume the cluster services on this node , run the below command,
~]# pcs cluster unstandby {Cluster_Node_Name}
Q:9 How to check the status of Quorum?
Ans: Current state of Quorum of your cluster can be viewed by the command line utility “corosync-quorumtool”
Execute the below command from any of the cluster node.
~]# corosync-quorumtool
Above command output will display the information regarding the quorum like Number of nodes, Quorate Status, Total Votes, Expected Votes and Quorum etc.
To keep running the running “corosync-quorumtool” use “-m” flag.