Configuring Red Hat High Interview Questions
| Question |
| What is High Availability Cluster? |
| Answer |
| High clusters provide highly available services by eliminating single points of failure and by failing over services from one cluster node to another in case a node becomes inoperative. |
| Question |
| What is Coro sync ? |
| Answer |
| Corosync uses the totem protocol for heartbeat like monitoring of the other nodes health. A token is passed around to each node..node does some work and then it passes the token on to the next node. This goes around and around all the time. Should a node not pass its token on after a short time out period, the token is declared lost, an error count goes up and a new token is sent. If too many tokens are lost in a row, the node is declared lost.Once the node is declared lost… the remaining nodes reform a new cluster… |
| Question |
| It says: kernel: CMAN: Cluster membership rejected. What do I do? |
| Answer |
| One or more of the nodes in your cluster is rejecting the membership of this node. Check the syslog /var/log/messages on all remaining nodes in the cluster for messages regarding why the membership was rejected. |
| Question |
| Is it a problem if node order isn’t the same for all nodes in cman_tool services? |
| Answer |
| No.. this is not a problem and can be ignored. Some nodes may report [1 2 3 4 5] while others report a different order… like [4 3 5 2 1]. This merely has to do with the order in which cman join messages are received… |
| Question |
| Can we configure it on rhel7 ? I mean it is available with rhel7 by default ? |
| Answer |
| Not available ..pacemaker by default |
| Question |
| Is there any Cluster name limitations ? |
| Answer |
| 15 non-NUL ASCII 0 characters |
| Question |
| Does cluster suite use multicast or broadcast? |
| Answer |
| By default…the older cluster infrastructure (RHEL4, STABLE and so on) uses broadcast and the newer cluster infrastructure with openais (RHEL5, HEAD and so on) uses multicast. |
| Question |
| In conga 2 node clustering common Lun how to create?I have onely 2 nodes. |
| Answer |
| Common lun is required from strorage mapped to both the nodes..that can be fc or iscsi .. for test setup you can you openfiler..u can configure using HA-LVM or GFS .. |
| Question |
| What is the minimum size of the Quorum Disk? |
| Answer |
| 10 MB |
| Question |
| How many nodes are supported in Red hat 6 Cluster? |
| Answer |
| 16 nodes |
| Question |
| What are types of clusters available in RHEL? |
| Answer |
| Storage, High availability, Load balancing, High performance |
| Question |
| Should I use power fencing or fabric fencing? |
| Answer |
| Both do the job… both methods guarantee the victim can not write to the file system.. thereby ensuring file system integrity. |
| Question |
| What is the order to stop the Red Hat Cluster services? |
| Answer |
| In Red Hat 5 service rgmanager stop service gfs stop service clvmd stop service cman stop In Red Hat 6 service rgmanager stop service gfs2 stop service clvmd stop service cman stop |
| Question |
| What is central inventory in Linux and how it works |
| Answer |
| It allows users and system administrator to easily install, update, remove or search software packages on a systems. |
| Question |
| Is manual fencing supported? |
| Answer |
| No. No… You can use it. but do not complain when a node needs to be fenced and the cluster locks up, and services do not fail over. |
| Question |
| What is the “Dirty” flag that cman_tool shows, and should I be worried? |
| Answer |
| No, you should not be worried… All this flag indicates is that there are cman daemons running that have state which cannot be rebuilt without a node reboot. |
| Question |
| How do I change the time interval for the heartbeat messages? |
| Answer |
| Just add hello_timer=”value” to the cman section in your cluster.conf file… |
| Question |
| Why quorum should be a physical partition and not should be a LVM in this cluster ? |
| Answer |
| lvm services are not up when system checks for quorum.. so it is not on lvm |
| Question |
| Is it possible to configure a cluster with nodes running on different networks (subnets)? |
| Answer |
| Yes, it is… if u configure the cluster to use multicast rather than broadcast there is an option for this in system-config-cluster then the nodes can be on different subnets… |
| Question |
| 1.what is fance device and the purpose we used it. 2. when votting is necessary. |
| Answer |
| A fence device is a hardware device that can be used to cut a node off from shared storage. This can be accomplished in a variety of ways: powering off the node via a remote power switch, disabling a Fibre Channel switch port |
| Question |
| If my cluster is mission-critical, can I override quorum rules and have a “last-man-standing” cluster that’s still functioning? |
| Answer |
| this may not be a good idea in most cases bcz of the dangers of split-brain, but there is a way you can do this: You can adjust the “votes” for the quorum disk to be equal to the number of nodes in the cluster, minus 1 |
| Question |
| What is the minimum configuration(HW) and package requirement for HA cluster with Conga. |
| Answer |
| Computers that are capable of running Red Hat Enterprise Linux 6 software, with at least 1GB of RAM. Luci and ricci packages |
| Question |
| What is luci and ricci in Red Hat Cluster? |
| Answer |
| luci is the server component of d Conga administration utility.conga is an integrated set of software components that provides centralized configuration & management of rhel clusters and storage. ricci is the client component of the Conga administration utility. this is an agent that runs on each computer managed by Conga.this service needs to be running on all the client nodes of the cluster. |
| Question |
| How can I rename my cluster? |
| Answer |
| Here is d procedure: 1.Unmount all GFS partitions and stop all clustering software on all nodes in the cluster. 2.Change name=””old_cluster_name”” to name=””new_cluster_name”” in /etc/cluster/cluster.conf 3. If you have GFS partitions in your cluster, you need to change their superblock to use the new name. For example: gfs_tool sb /dev/vg_name/gfs1 table new_cluster_name:gfs1 4. Restart the clustering software on all nodes in the cluster. 5. Remount your GFS partitions |
| Question |
| How can I define a two-node cluster if a majority is needed to reach quorum? |
| Answer |
| We had to allow two-node clusters, so we made a special exception to the quorum rules. There is a special setting “two_node” in the /etc/cluster.conf file that looks like this: |
| Question |
| What happens when a node that’s holding a lock gets fenced or is rebooted? |
| Answer |
| Nodes locks should be freed up. |
| Question |
| Do I really need a shared disk to use QDisk? |
| Answer |
| Yes. there hv been suggestions to make qdiskd operate in a ‘diskless’ mode in order to help prevent a fence-race that is prevent a node from attempting to fence another node, but no work has been done in this area yet. |
| Question |
| I removed a node from cluster.conf but the cluster software and services kept running. What did I do wrong? |
| Answer |
| You are supposed to stop the node before removing it from the cluster.conf. |
| Question |
| Are the quorum disk votes reported in “Total_votes” from cman_tool nodes? |
| Answer |
| Yes.. if the quorum disk is registered correctly with cman you should see the votes it contributes and also it is “node name” in cman_tool nodes. |
| Question |
| If we have two cluster nodes with quorum disk connected with FC if one FC port downs server fences it is normal behavior or not ? Note: there are two- two FC port available with multiparty configured and working fine |
| Answer |
| It should not fence.. as we have multipath for fc.. |
| Question |
| What if the fenced node comes back up and still can’t contact the other? Will it corrupt my file system |
| Answer |
| Two_node cluster.conf option allows one node to have quorum by itself. A network partition between the nodes won’t result in a corrupt fs because each node will try to fence the other when it comes up prior to mounting gfs. |
| Question |
| If both nodes in a two-node cluster lose contact with each other, don’t they try to fence each other? |
| Answer |
| they do. when each node recognizes that the other has stopped responding, it will try to fence the other. |
| Question |
| What if I change my mind? Can I change which locking protocol to use? |
| Answer |
| Easy to change the locking protocol for a GFS file system: gfs_tool sb proto |
| Question |
| What is the recommended way to configure multiple heartbeat channels? |
| Answer |
| Channel bonding. |
| Question |
| What is the ‘depth’ of an action in an rgmanager script? |
| Answer |
| Depth means how intensive of a check. There used to be 0, 10 and 20. 0 was Is the IP still there?.. 10 was can I ping it and is the ethernet link up? 20 used to Attempt to ping the router… |
| Question |
| How do I specify which locking protocol to use? |
| Answer |
| u specify the locking protocol when you make your file system with gfs_mkfs or mkfs.gfs2 |
| Question |
| What is the order in which we will start the Red Hat Cluster services in RHEL 5/6? |
| Answer |
| In RedHat 5 service cman start service clvmd start service gfs start service rgmanager start In Red Hat 6 service cman start service clvmd start service gfs2 start service rgmanager start |
| Question |
| Is there any way to do NIC failover other than channel bonding? |
| Answer |
| No , not really. The channel bonding driver is designed for this purpose. When used with a good internally redundant switch that supports trunking..you end up with higher bandwidth and increased availability. |
| Question |
| What is a lock manager ? |
| Answer |
| lock manager is a traffic cop who controls access to resources in the cluster…such as access to a GFS file system. |
| Question |
| Where are rgmanager’s scripts located? |
| Answer |
| /usr/share/cluster/* |
| Question |
| Share me the cluster configuration step? |
| Answer |
| You can download detailed installation step by step guide from google… basic steps are as below: a)Configure Storage/udev/multipathing b) Test file systems by mounting on both nodes c) Install application on both nodes and copy required folders/data to shared storage d) Write the startup/shutdown/status scripts, if required (you can use standard sysv inti scripts as well, if you application has one) e) Mount the shared partition on node1 and test the app f) Unmount shared partition from node1, mount in node2 and test the app g) Test fencing from both nodes h) install cman, rgmanager rpms i) Ensure iptables and selinux do not interfere (setenforce 0 for selinux) |
| Question |
| Can I control where rgmanager logs or its log level? |
| Answer |
| Yes you can.. u will be able to have rgmanager log to different places and a different level by changing the cluster/rm tag. For eg.. |
| Question |
| What is the command used to relocate a service to another node? |
| Answer |
| clusvcadm -r servicename -m nodename |
| Question |
| Can I have a mixed cluster with some nodes at RHEL4U1 and some at RHEL4U2? |
| Answer |
| You can not mix rhel4 U1 and U2 systems in a cluster bcz there were changes between U1 and U2 that changed the format of internal messages that are sent around the cluster. |
| Question |
| BH838684 10th, March 2015 | 11:24 AM If we have two cluster nodes with quorum disk connected with FC if one FC port downs server fences it is normal behavior or not ? Note: there are two- two FC port available with multiparty configured and working fine to remove this probkem what we cab do? |
| Answer |
| set totem timeout to be larger than the amount of time it takes for a path to fail |
| Question |
| How does NetworkManager service affects Red Hat Cluster? |
| Answer |
| Use of networkmanager is not supported on cluster nodes. if u hv installed networkmanager on ur cluster nodes, you should either remove it or disable it. |
