How to Install and Configure HA Cluster with PCS on Debian

Why HA?

High-availability software is used to operate high-availability clusters. In a high-availability IT system, there are different layers (physical, data link, network, transport, session, presentation, and application) that have different software needs. If a server in the cluster fails, another server or node can take over immediately to help ensure the application or service supported by the cluster remains operational. Using high-availability clusters helps ensure there is no single point of failure for critical IT and reduces or eliminates downtime. HA is a critical feature for your servers. Using HA Clusters should be good searced there are many diffrent HA structure (Data, Traffic, Load balancing, A/A, A/P …)

Prerequisites

Today I will try to tell creating HA Cluster with Pacemaker and Corosync with 2 Debian 10 VM. We need to have 2 different Linux VM for creating a cluster. Be aware that necessary security rules (Firewall, ssh and some ports depends of your Linux distro) and networking(2 dynamic or static IP) should be done.

Install Pacemaker and Corosync

1. The first step is to install PCS, Pacemaker and Corosync on both nodes. To do this, open terminal and run following command −

sudo apt install pcs corosync pacemaker

Configure Cluster

The next step is to configure cluster. We will start by configuring Corosync cluster messaging system. To do this, open file /etc/corosync/corosync.conf in your preferred text editor and add following lines −

totem {
   version: 2
   secauth: off
   cluster_name: mycluster
   transport: udpu
}

nodelist {
   node {
      ring0_addr: 192.168.64.13
      name: debian1
   }

   node {
      ring0_addr: 192.168.64.14
      name: debian2
   }
}

• IP addresses depend on your VM’s IP ring0_addr: 192.168.64.13, ring0_addr: 192.168.64.14
• Hostnames can be different for your VMs.
• There are different type Cluster configs.

Start Corosync Service

1. You should start the service

sudo systemctl start corosync

Configure Pacemaker Cluster Resource Manager

The next step is to configure Pacemaker cluster resource manager. To do this, open file /etc/pacemaker/pcs.conf in your preferred text editor and add following lines

pcs cluster setup --name mycluster <hostname of node 1> <hostname of node 2>
pcs cluster enable --all

Replace <hostname of node 1> and <hostname of node 2> with hostnames of two nodes.

Configure Cluster Resources

The final step is to configure cluster resources. We need start by configuring a virtual IP (Floating IP) for HA. Floating IPs (now named Reserved IPs). A Floating IP is an IP address that can be instantly moved from one Droplet to another Droplet in the same datacenter.

pcs resource create virtual_ip ocf:heartbeat:IPaddr2 ip=<IP address of virtual IP> cidr_netmask=24 op monitor interval=30s

• You can create a IP Which has same sub-net as your VMs
• You can verify the Virtual IP with:

sudo pcs config

• We can add a Apache resources for testing the web server.
• Configure a simple Apache web server that will be used to test cluster. To do this, run following command

pcs resource create apache ocf:heartbeat:apache

• Apache2 should be installed before it.
• This command will create a cluster resource for Apache web server. You can now access web server by navigating to virtual IP address in your web browser.

Verify Cluster Status

• You can verify and see the cluster status with : ‘pcs status’ command.
• If you got error restart the services for both nodes.

• I ran the command in the Debian2 node and You can see Debian1 is active now and all traffic and resources running on the Debian1.

• Right now I can reach Debian1’s Web server

• I will disable the Debian1’s Pacemaker service and I will try to connect Web server again.

sudo systemctl stop pacemaker

• Here is the Debian2 hosts all resources
• If you hit the VirtualIP you can get reply from it.

Never stop learning, beacuse life never stops teaching.

Thanks for reading.

Guneycan Sanli.

Guneycan Sanli

A person who like learning, music, travelling and sports.

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