pacemaker

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), or enabling multicast on the network switches. Firewall issues Incorrectly configured firewalls can make … [Read more...] about Troubleshooting Pacemaker Cluster Networking

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 increase the failcount for a resource. This count can be viewed with the command: # pcs resource failcount show [RESOURCE] Failure to start or stop … [Read more...] about Troubleshooting Resource Failures in Pacemaker Cluster

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 started or stopped, the MailTo resource will send an email to the configured address. For example, to add a Mail To resource to the important group resource group, … [Read more...] about How to Configure Pacemaker Cluster Notifications

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 to_file and logfile directives can be added to the logging {} block. logging { to_file: yes logfile: … [Read more...] about How to Configure Cluster Logging for Corosync and Pacemaker

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, or to move a resource or resource group away from the node it is currently running on, and temporarily prohibit the resource from … [Read more...] about Managing resources in a pacemaker cluster (stop/start and relocate resource groups in a running cluster)

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 be combined into resource groups that will force all resources in a group to start and stop at the same time, on the same node, creating clustered services for consumers. … [Read more...] about How to Create and Configure Resource Groups in a Pacemaker Cluster

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 order to accomplish this, resources are controlled by resource agents. Pacemaker can manage different kinds of resource agents: AgentPurpose LSBLinux Standard … [Read more...] about How to Create and Configure Resources in a Pacemaker Cluster

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 agents shipped with Red Hat Enterprise Linux High Availability Add-on: stonith-timeout This setting defines the time to wait for fencing … [Read more...] about Configuring Cluster Fencing Agents in a Pacemaker Cluster

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 fence devices. The pcs stonith list provides a list of all installed fencing agents: # pcs stonith list fence_apc - Fence agent for APC over … [Read more...] about Setting Up Fencing Devices in a Pacemaker Cluster

What is fencing? The Red Hat High Availability Add-on uses fencing to ensure data integrity in the cluster. Fencing is often accomplished by powering the node off since a dead node is clearly not able to do anything. In other cases, a combination of operations will be used to cut the node off from the network (to stop new work from arriving) or from storage (to stop the node from writing to shared storage). Fencing is a necessary step in service and resource recovery in a cluster. The Red Hat … [Read more...] about What is fencing and What are different methods of fencing in a pacemaker cluster