Linux - HA Cluster Maintenance

Linux - HA Cluster Maintenance

What is a cluster ? 

A group or collection of servers that is providing same service/application. 

In this blog we will see about setting cluster into maintenance mode and releasing cluster out of maintenance mode. 

What is Maintenance mode ? 

Maintenance mode is when the server is not available to service the customers and is currently undergoing a maintenance task. 

With HA Cluster enabled, If we need to perform some activity on the cluster managed pools/servers, we will need to enable cluster maintenance mode so that you do not see any unexpected behaviors from the system.

To enable cluster Maintenance following command is used. 

For SUSE Clusters 

crm configure property maintenance-mode=true

For Redhat Cluster

pcs property set maintenance-mode=true

When you have enabled/set the Maintenance mode you can perform start/stop or any config update on the cluster managed resources. During this period cluster will not interfere with these resources. 

Once we have completed the required activity to release cluster from maintenance mode following command is used. 

For SUSE Clusters 

crm configure property maintenance-mode=false

For Redhat Cluster

pcs property set maintenance-mode=false

Creating and modifying user in Linux

Creating and modifying user in Linux

    By default when you Install Linux Operating system a user will be created and that user will have full sudo privilege. However when ever you create a user after installing OS, you will need to provision required privilege for that user. In this blog i will show you few commands with useradd and usermod. 

    The following user karthick has been created when OS was installed and this user is added to the Wheel group to get the sudo privilege. User karthick can run privileged commands with his password. 

    To create a normal user in command line providing the users home directory and UID we will use as -d to specify user home directory and -u for UID.

#useradd -d <Path_To_User's_HomeDirectory> -u UID

UID is a unique identifier number used to identify the user. 

    This user does not have privilege to execute root level commands. However if we need to provide root access we will need to add this user to wheel group. To do so we will use usermod command

Adding users to this wheel group will gain complete root access for the user. 

    If you do not want user to have complete root access and instead provide granular or role based access we can provision that through sudo template. you can create a sudoers template/drop-in file under /etc/sudoers.d directory. 

We will see about sudoers template file in much more detail in upcoming blogs.