Configuring A High Availability Cluster On RHEL/CentOS

This guide shows how you can set up a two node, high-availability HTTP cluster with heartbeat on RHEL/CentOS. Both nodes use the Nginx web server to serve the same content.

Pre-Configuration Requirements

1. Assign hostname nginx-primary to primary node with IP address 192.168.100.203 to eth0.


2. Assign hostname nginx-slave to slave node with IP address 192.168.100.204 to eth0.

Note: on nginx-primary

uname -n

must return nginx-primary.

On nginx-slave

uname -n

must return nginx-slave.

192.168.100.9 is the virtual IP address that will be used for our Nginx webserver (i.e., Nginx will listen on that address).

Assume that Nginx web server has been installed and configured correctly on both nodes.

Configuration

1. Download and install the heartbeat package on both nodes. In our case we are using RHEL/CentOS so we will install heartbeat with yum:

yum install heartbeat

2. Now we have to configure heartbeat on our two node cluster. We will deal with three files. These are:

authkeys
ha.cf
haresources

3. Now moving to our configuration. But there is one more thing to do, that is to copy these files to the /etc/ha.d directory. In our case we copy these files as given below:

cp /usr/share/doc/heartbeat-2.1.4/authkeys /etc/ha.d/
cp /usr/share/doc/heartbeat-2.1.4/ha.cf /etc/ha.d/
cp /usr/share/doc/heartbeat-2.1.4/haresources /etc/ha.d/


4. Now let's start configuring heartbeat. First we will deal with the authkeys file, we will use authentication method 2 (sha1). For this we will make changes in the authkeys file as below.

vi /etc/ha.d/authkeys

Then add the following lines:


auth 2
2 sha1 test-nginx-ha


Change the permission of the authkeys file:

chmod 600 /etc/ha.d/authkeys

5. Moving to our second file (ha.cf) which is the most important. So edit the ha.cf file with vi:

vi /etc/ha.d/ha.cf

Add the following lines in the ha.cf file:


logfile /var/log/ha-log
logfacility local0
keepalive 2
deadtime 30
initdead 120
bcast eth0
udpport 694
auto_failback on
node nginx-primary
node nginx-slave


Note: nginx-primary and nginx-slave is the output generated by

uname -n

6. The final piece of work in our configuration is to edit the haresources file. This file contains the information about resources which we want to highly enable. In our case we want the webserver (nginx) highly available:

vi /etc/ha.d/haresources

Add the following line:


nginx-primary 192.168.100.9 nginx



7. Copy the /etc/ha.d/ directory from nginx-primary to nginx-slave:

scp -r /etc/ha.d/ root@nginx-slave:/etc/

8. Create the file index.html on both nodes:

On nginx-primary:

echo "nginx-primary test server" > /usr/html/index.html

On nginx-slave:

echo "nginx-slave test server" > /usr/html/index.html

9. Now start heartbeat on the primary nginx-primary and slave nginx-slave:

/etc/init.d/heartbeat start

10. Open web-browser and type in the URL:

http://192.168.100.9

It will show "nginx-primary test server".

11. Now stop the hearbeat daemon on nginx-primary:

/etc/init.d/heartbeat stop

In your browser type in the URL http://192.168.100.9 and press enter.

It will show "nginx-slave test server".

12. We don't need to create a virtual network interface and assign an IP address (192.168.100.9) to it. Heartbeat will do this for you, and start the service (nginx) itself. So don't worry about this.
    
    Don't use the IP addresses 192.168.100.203 and 192.168.100.204 for services. These addresses are used by heartbeat for communication between nginx-primary and nginx-slave. When any of them will be used for services/resources, it will disturb hearbeat and will not work. Be carefull!!!