How to Install and Configure Cluster with Two Nodes in Linux?

In today's era, the use of clusters has become increasingly important in the field of computing. A cluster is a group of interconnected computers that work together as a single entity to provide high-performance computing, data analysis, and fault tolerance. In this tutorial, we will demonstrate how to install and configure a two-node cluster in Linux using Pacemaker and Corosync.

A cluster consists of two or more nodes that work together as a single system. Each node is a separate computer with its own resources (CPU, memory, storage) connected through a network for communication and resource sharing. Pacemaker acts as the cluster resource manager that manages service availability, while Corosync provides the cluster messaging system for inter-node communication.

Prerequisites

• Two Linux servers (CentOS 7/8 or RHEL recommended)

• Static IP addresses configured on both nodes

• Proper hostname resolution between nodes

• Root or sudo access on both systems

• Firewall configured to allow cluster traffic

Cluster Architecture Overview

Step 1 Install Required Packages

Install Pacemaker and Corosync on both nodes:

sudo yum install -y pacemaker corosync pcs fence-agents-all

Enable and start the pcsd service for cluster management:

sudo systemctl enable pcsd
sudo systemctl start pcsd

Step 2 Configure Firewall

Open necessary ports for cluster communication:

sudo firewall-cmd --permanent --add-service=high-availability
sudo firewall-cmd --permanent --add-port=2224/tcp
sudo firewall-cmd --permanent --add-port=5405/udp
sudo firewall-cmd --reload

Step 3 Set Up Cluster Authentication

Set a password for the hacluster user on both nodes:

sudo passwd hacluster

From Node 1, authenticate with both nodes:

sudo pcs host auth node1 node2 -u hacluster -p password

Step 4 Create and Configure the Cluster

Initialize the cluster from Node 1:

sudo pcs cluster setup mycluster node1 node2
sudo pcs cluster enable --all
sudo pcs cluster start --all

Verify cluster status:

sudo pcs cluster status

Cluster Status:
 Cluster Summary:
   * Stack: corosync
   * Current DC: node1 (version 2.0.5-9.el8_4.3-ba59be7122)
   * Last updated: Mon Jan 01 12:00:00 2024
   * 2 nodes configured
   * 0 resource instances configured

Step 5 Disable STONITH and Configure Quorum

For a two-node cluster, disable STONITH and configure quorum policy:

sudo pcs property set stonith-enabled=false
sudo pcs property set no-quorum-policy=ignore

Step 6 Create Cluster Resources

Virtual IP Resource

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

Apache Web Server Resource

sudo pcs resource create webserver ocf:heartbeat:apache \
    configfile="/etc/httpd/conf/httpd.conf" \
    statusurl="http://localhost/server-status" \
    op monitor interval=1min

Group Resources Together

sudo pcs resource group add web_group virtual_ip webserver

Step 7 Verify Cluster Configuration

Check cluster status and resource configuration:

sudo pcs status

Cluster name: mycluster
Cluster Summary:
  * Stack: corosync
  * Current DC: node1
  * 2 nodes configured
  * 2 resource instances configured

Node List:
  * Online: [ node1 node2 ]

Full List of Resources:
  * Resource Group: web_group
    * virtual_ip     (ocf::heartbeat:IPaddr2):        Started node1
    * webserver      (ocf::heartbeat:apache):         Started node1

Step 8 Test Failover

Simulate node failure by putting a node in standby mode:

sudo pcs node standby node1

Verify resources migrate to the other node:

sudo pcs status

Bring the node back online:

sudo pcs node unstandby node1

Network Topology Considerations

Common Troubleshooting Commands

# Check cluster configuration
sudo pcs config

# View cluster logs
sudo journalctl -u corosync
sudo journalctl -u pacemaker

# Reset cluster configuration
sudo pcs cluster destroy

Conclusion

Setting up a two-node cluster in Linux using Pacemaker and Corosync provides high availability for critical services. The cluster automatically manages resource failover between nodes, ensuring service continuity. Proper testing, monitoring, and maintenance are essential for production deployments to ensure reliable cluster operation.