Cluster configuration is a critical task for ensuring high availability, scalability, and reliability of services in a Linux environment. Clusters allow multiple servers (nodes) to work together as a single system, providing redundancy and load balancing. This article will guide you through the process of setting up a basic High Availability (HA) cluster using Pacemaker and Corosync on Linux. These tools are widely used in the industry for managing cluster resources and ensuring service continuity.

Examples:

1. Install Required Packages

   First, you need to install the necessary packages. On a Debian-based system, you can use the following commands:

   sudo apt-get update
   sudo apt-get install pacemaker corosync pcs

   On a Red Hat-based system, the commands would be:

   sudo yum install pacemaker corosync pcs

2. Configure Corosync

   Corosync handles the communication between the nodes. You need to configure it by editing the /etc/corosync/corosync.conf file. Here is an example configuration:

   totem {
      version: 2
      secauth: on
      cluster_name: my_cluster
      transport: udpu
      interface {
          ringnumber: 0
          bindnetaddr: 192.168.1.0
          mcastport: 5405
      }
   }
   quorum {
      provider: corosync_votequorum
      two_node: 1
   }

   Make sure to replace bindnetaddr with your network address.

3. Start and Enable Corosync and Pacemaker

   After configuring Corosync, you need to start and enable both Corosync and Pacemaker services:

   sudo systemctl start corosync
   sudo systemctl enable corosync
   sudo systemctl start pacemaker
   sudo systemctl enable pacemaker

4. Authenticate Nodes

   Use the pcs command to authenticate the nodes. Replace node1 and node2 with the hostnames or IP addresses of your nodes:

   sudo pcs cluster auth node1 node2

5. Create the Cluster

   Now, create the cluster:

   sudo pcs cluster setup --name my_cluster node1 node2
   sudo pcs cluster start --all

6. Check Cluster Status

   Verify the status of your cluster:

   sudo pcs status

7. Add Resources

   Add resources to your cluster, such as a virtual IP address or a service. For example, to add a virtual IP:

   sudo pcs resource create ClusterIP ocf:heartbeat:IPaddr2 ip=192.168.1.100 cidr_netmask=24 op monitor interval=30s

   To add an Apache service:

   sudo pcs resource create WebSite ocf:heartbeat:apache configfile=/etc/httpd/conf/httpd.conf op monitor interval=30s