pacemaker

In this post, lets see how resource groups can be used to control resource startup order by configuring an active/passive NFS server resource group. What are constraints? Constraints are restrictions that determine the order in which resources can be started and stopped, on which nodes they can run, or which other resources they can share […]

Identifying network issues Faulty, or misconfigured, network connections can wreak havoc on a cluster. The following is a list of possible issues and fixes. Unicast-only networks Some network switches actively block multicast traffic. If a cluster transport is set to udp, this enables multicast communications. Possible fixes include switching the traffic to udpu (UDP Unicast), […]

Resource failures Resources can fail for multiple reasons. An administrator might have used incorrect settings when defining the resource, a configuration file might have an error in it, the system might be trying to start a resource that does not exist, or some other unforeseen issue might occur. Whenever a resource fails, the cluster will […]

Configuring MailTo notifications Most system administrators like to be notified when a resource migrates to a different node since this is typically an indication of trouble with a node. One of the easiest ways to get notifications of this sort is to add a MailTo resource to a resource group. Whenever the resource group is […]

Corosync logging When troubleshooting a cluster, one of the most useful resources at a system administrator’s disposal is the system log. The corosync daemon will log to syslog by default, but logging can be controlled inside the logging {} block in /etc/corosync/corosync.conf. Logging to a file To enable logging corosync messages to a file, the […]

Managing services The Red Hat High Availability Add-on allows a cluster administrator to control the resources and resource groups running in the cluster. Resources and resource groups may be started and stopped by the cluster administrator. Restrictions can be enforced to temporarily prohibit a resource or resource group from migrating to a specific cluster node, […]

Configuring resource groups In most cases, having the cluster run individual resources is not an ideal situation. Mounting a file system with web content on one node, starting an httpd instance on a second, and assigning a floating IP address to a third node does not create a service that consumers can use. Resources can […]

Resources Clustered services consist of one or more resources. A resource can be an IP address, a file system, or a service like httpd, among others. All the bits required to provide a service to consumers are a resource. With the Red Hat High Availability Add-on, all resources are monitored independently from each other. In […]

Creating a fence device A system administrator can create a fence device in the cluster with the pcs stonith create command: # pcs stonith create name fencing_agent parameters The command requires additional arguments, such as the fencing agent and the fencing parameters required for the fencing agent. There are generic properties for all the fencing […]

Overview of fence device configuration Fencing is a requirement for every operational cluster. The first step when setting up fencing for the cluster is the setup of the hardware or software device that does the actual fencing. The Red Hat Enterprise Linux High Availability Add-on provides a variety of fencing agents for use with different […]