|Managing Serviceguard Fifteenth Edition > Chapter 5 Building
an HA Cluster Configuration
This section describes some approaches to routine management of the cluster. Additional tools and suggestions are found in Chapter 7, “Cluster and Package Maintenance.”
You can check configuration and status information using Serviceguard Manager: from the System Management Homepage (SMH), choose Tools-> Serviceguard Manager.
Serviceguard also provides several commands for control of the cluster:
You can use these commands to test cluster operation, as in the following:
Additional cluster testing is described in Chapter 8 “Troubleshooting Your Cluster”. Refer to Appendix A for a complete list of Serviceguard commands. Refer to the Serviceguard Manager Help for a list of Serviceguard Administrative commands.
It is important to prevent LVM volume groups that are to be used in packages from being activated at system boot time by the /etc/lvmrc file. One way to ensure that this does not happen is to edit the /etc/lvmrc file on all nodes, setting AUTO_VG_ACTIVATE to 0, then including all the volume groups that are not cluster-bound in the custom_vg_activation function. Volume groups that will be used by packages should not be included anywhere in the file, since they will be activated and deactivated by control scripts.
Automatic startup is the process in which each node individually joins a cluster; Serviceguard provides a startup script to control the startup process. Automatic cluster start is the preferred way to start a cluster. No action is required by the system administrator.
There are three cases:
To enable automatic cluster start, set the flag AUTOSTART_CMCLD to 1 in the /etc/rc.config.d/cmcluster file on each node in the cluster; the nodes will then join the cluster at boot time.
Here is an example of the /etc/rc.config.d/cmcluster file:
You may find it useful to modify the system's login message to include a statement such as the following:
You might wish to include a list of all cluster nodes in this message, together with additional cluster-specific information.
The /etc/issue and /etc/motd files may be customized to include cluster-related information.
The number of nodes you will need for your Serviceguard cluster depends on the processing requirements of the applications you want to protect. You may want to configure a single-node cluster to take advantage of Serviceguard’s network failure protection.
In a single-node cluster, a cluster lock is not required, since there is no other node in the cluster. The output from the cmquerycl command omits the cluster lock information area if there is only one node.
You still need to have redundant networks, but you do not need to specify any heartbeat LANs, since there is no other node to send heartbeats to. In the cluster configuration ASCII file, specify all LANs that you want Serviceguard to monitor. For LANs that already have IP addresses, specify them with the STATIONARY_IP keyword, rather than the HEARTBEAT_IP keyword. For standby LANs, all that is required is the NETWORK_INTERFACE keyword with the LAN device name.
Single-node operation occurs in a single-node cluster or in a multi-node cluster, following a situation where all but one node has failed, or where you have shut down all but one node, which will probably have applications running. As long as the Serviceguard daemon cmcld is active, other nodes can re-join the cluster at a later time.
If the Serviceguard daemon fails when in single-node operation, it will leave the single node up and your applications running. This is different from the loss of the Serviceguard daemon in a multi-node cluster, which halts the node with a system reset, and causes packages to be switched to adoptive nodes.
It is not necessary to halt the single node in this scenario, since the application is still running, and no other node is currently available for package switching.
However, you should not try to restart Serviceguard, since data corruption might occur if the node were to attempt to start up a new instance of the application that is still running on the node. Instead of restarting the cluster, choose an appropriate time to shutdown and reboot the node, which will allow the applications to shut down and then permit Serviceguard to restart the cluster after rebooting.
Ignore this section unless you have a particular need to disable identd.
You can configure Serviceguard not to use identd.
If you must disable identd, you can do so by adding the -i option to the tcp hacl-cfg and hacl-probe commands in /etc/inetd.conf.
As root user, you can delete a cluster configuration from all cluster nodes by using Serviceguard Manager or the command line. The cmdeleteconf command prompts for a verification before deleting the files unless you use the -f option. You can delete the configuration only when the cluster is down. The action removes the binary configuration file from all the nodes in the cluster and resets all cluster-aware volume groups to be no longer cluster-aware.
Although the cluster must be halted, all nodes in the cluster should be powered up and accessible before you use the cmdeleteconf command. If a node is powered down, power it up and boot. If a node is inaccessible, you will see a list of inaccessible nodes together with the following message:
Reply Yes to remove the configuration. Later, if the inaccessible node becomes available, you should run the cmdeleteconf command on that node to remove the configuration file.