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
Linux
How to find and delete files older than some particular time period in Linux
Searching by file timestamp Unix/Linux filesystems have three types of timestamp on each file. They are as follows: Access time (-atime): The timestamp when the file was last accessed. Modification time (-mtime): The timestamp when the file was last modified. Change time (-ctime): The timestamp when the metadata for a file (such as permissions or ownership) was last modified. Search and delete file older than 7 days Lets take an example, wherein we will find and delete file older … [Read more...] about How to find and delete files older than some particular time period in Linux
“-bash: firewall: command not found” – How to resolve in CentOS/RHEL 7
The Problem Why is the below error observed when the firewall-cmd --state command is executed: -bash: firewall: command not found The Solution If there is a syntax error while executing the command, one may get the error of the following sorts :- # firewall-cmd -state usage: see firewall-cmd man page firewall-cmd: error: unrecognized arguments: -state # firewall -cmd --state -bash: firewall: command not found stop firewalld in CentOS/RHEL 7 The below command may be executed to … [Read more...] about “-bash: firewall: command not found” – How to resolve in CentOS/RHEL 7
Troubleshooting Resource Failures in Pacemaker Cluster
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
How to Configure Pacemaker Cluster Notifications
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
How to Configure Cluster Logging for Corosync and Pacemaker
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 resources in a pacemaker cluster (stop/start and relocate resource groups in a running cluster)
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)
How to configure a systemd service to wait for a specific mount point to be mounted before starting
The ask: An installed service needs a specific filesystem (for example NFS) to be mounted in order to function properly. An attempt to start said service before the filesystem is mounted correctly results into fail. (if this happens during boot, boot time gets delayed and the service is not running after the boot sequence). How to configure the service file so that sytemd will always wait for the said mount to start the service? 1. The RequiresMountsFor option may be used. As per systemd.unit … [Read more...] about How to configure a systemd service to wait for a specific mount point to be mounted before starting
How to Create and Configure Resource Groups in a Pacemaker 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
How to Create and Configure Resources 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