In this tutorial, we will show you how to set up Nginx High Availability cluster using Pacemaker on CentOS 7. To have an Nginx server that can operate continuously without failure for a long time, we need to configure the server with active-passive Nginx instances.  Pacemaker is an open source cluster manager software that achieves maximum high availability of your services. It’s an advanced and scalable High Availability cluster manager distributed by ClusterLabs, it manages all cluster services and use the messaging and membership capabilities of the underlying cluster engine.

1. Prerequisites

To follow this tutorial, you need to have:

  • 2 or more servers
  • CentOS 7 Operating System
  • root access to each of the servers

2. Login and Update CentOS

ssh root@IP_Address -p7022
yum update
yum upgrade

Edit /etc/hosts file on both server with any terminal text editor of your liking

nano /etc/hosts

Add the following lines to /etc/hosts file

192.168.0.22    webserver-01
192.168.0.23    webserver-02

3. Install Epel Repository and Nginx

Extra Packages for Enterprise Linux (EPEL) repository is needed in order to install Nginx. Run the following commands on both servers.

yum install epel-release -y

yum install nginx -y
systemctl enable nginx
systemctl start nginx

4. Change default Nginx index page

Once finished, we need to make changes to the default Nginx index page on both server.

Run the following command on server one

echo ‘

webserver-01

’ > /usr/share/nginx/html/index.html

Run the following command on server two

echo ‘

webserver-02

’ > /usr/share/nginx/html/index.html

5. Install and configure Pacemaker

In this section, we will install the Pacemaker stack. You have to complete this step on both servers.

yum install corosync pacemaker pcs -y

After the installation has been completed, enable all services to launch automatically at system boot using the systemctl commands below.

systemctl enable pacemaker
systemctl enable corosync
systemctl enable pcsd

6.  Synchronize the configuration

The installation will create a ‘hacluster’ system user. We also need to run pcsd in order to synchronize the configuration

systemctl start pcsd

7. Create a password

Next, create a new password for ‘hacluster’ user that had been automatically created during the previous installation, we need to use the same password for all servers

passwd hacluster

8. Create Clusters

Next, run this command below

pcs cluster auth webserver-01 webserver-02

At this point, we are ready to set up the cluster.

pcs cluster setup –name rosecluster webserver-01 webserver-02

rosecluster is the cluster name, while webserver-01 and webserver-02 are the servers that will be the parts of rosecluster.

Enable it on boot and start it now.

pcs cluster enable –all
pcs cluster start –all

We can check the cluster status with this command:

pcs status

9. Disable STONITH

STONITH or Shoot The Other Node In The Head is the fencing implementation on Pacemaker. If you’re in production, it’s better to enable STONITH. Since we’re not using the fencing device, we will disable the STONITH.

When running pcs status command, you will see a warning in the output saying that no STONITH devices are configured and STONITH is not disabled:
WARNING: no stonith devices and stonith-enabled is not false

Disable STONITH with the following pcs command.

pcs property set stonith-enabled=false

10. Ignore the Quorum Policy

In this tutorial, we will configure Pacemaker to ignore quorum:

pcs property set no-quorum-policy=ignore

Check the property list and make sure stonith and the quorum policy are disabled.

pcs property list

11. Add Resources

Floating IP is the IP address that can be instantly migrated from one server to another in the same network, it is used to support failover in a high-availability cluster. In this tutorial, the floating IP address for the Pacemaker High-Availability will be ‘192.168.0.100’. For now, we are going to add two resources, the Floating IP address resource with the name ‘v_ip’ and a new resource for the Nginx web server named ‘webserver’.

Add the new floating IP address ‘v_ip’ using the following command.

pcs resource create v_ip ocf:heartbeat:IPaddr2 ip=192.168.0.100 cidr_netmask=32 op monitor interval=20s

Next, we can add the second resource to the cluster. The resource agent of the service is ocf:heartbeat:nginx named ‘webserver’.

pcs resource create webserver ocf:heartbeat:nginx configfile=/etc/nginx/nginx.conf op monitor timeout=”5s” interval=”5s”

Make sure there is no error, then check the resources.

pcs status resources

If you see two resources; ‘v_ip’ and ‘webserver’, it means the Floating IP and Nginx web server have been added.

12. Configure Constraints

In this step, we will tell the server to make both resources created earlier to be running on the same host. We will set collocation constraint for the resources with a score of INFINITY.

pcs constraint colocation add webserver v_ip INFINITY

Set Nginx resource (webserver) to always run on the same host where v_ip is active.

pcs constraint order v_ip then webserver

To check the resources are running on the same host, we can invoke:

pcs status

13. Test the cluster.

Navigate to http://192.168.0.100 on your web browser, you will see the default Nginx page from the webserver-01.

 

Then, invoke the following command to stop the cluster on the webserver-01:

pcs cluster stop webserver-01

Now, if you refresh the page at http://192.168.0.100, you will get the default Nginx page from the webserver-02.

 

Congratulation, you have successfully set up an Nginx High Availability active-passive cluster with Pacemaker. If you have a very busy website, you may consider running your website on an Nginx HA. There are many well known websites running on Nginx HA and they use Nginx HA to deliver their content quickly, reliably, and securely.


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