Guide to DNS Cluster Configuration

(Home >> Cluster/Remote Access >> Configure Cluster)

Overview

A DNS cluster is a group of nameservers that share records. A DNS cluster allows you to physically separate your nameservers so that if a web server loses its connection, you still have DNS functionality. This will allow visitors to reach websites on your server more quickly after the web server comes back online.

Note: The cPanel DNS cluster feature only provides redundancy for DNS. It does not add Apache or any other services to a cluster configuration.

To configure your DNS cluster, you will need two servers with cPanel DNSONLY installed. You will also need at least one web server with cPanel & WHM installed.

• cPanel DNSONLY is software that allows you to run a dedicated physical nameserver. It should only be installed on nameservers with no previous content on them.
• You can download the cPanel DNSONLY software for free.
• All machines in the cluster must have cPanel & WHM or cPanel DNSONLY version 11 or higher installed. Some features may not work with older versions of cPanel & WHM.
• You can have multiple cPanel DNSONLY servers and multiple cPanel & WHM servers in a cluster.

Enable DNS Clustering on each server

To enable DNS clustering in WHM, follow these steps:

1. Navigate to WHM’s Configure Cluster screen. (Home >> Cluster/Remote Access >> Configure Cluster).
2. In the Modify Cluster Status box, select Enable DNS Clustering.
3. Click Change.
4. Click Return to Cluster Status.

Selecting 'Enable DNS Clustering' to turn on clustering.

Note: You will also follow these steps if you wish to add a replacement server to the cluster.

You have now enabled DNS clustering. Next, specify which server(s) you wish to cluster.

• You will need to sync each web server to its DNS servers.
• You do not need to link dedicated DNS servers to each other, or link dedicated web servers to each other.

Global Cluster Options

This section allows you to specify the number of dnsadmin commands that are allowed to fail before WHM disables an unresponsive cluster member. You can improve the performance of your server if you choose to disable unresponsive cluster members .

To configure the failure threshold for servers in the cluster, follow these steps:

1. Select an option in the Global Cluster Options box.
   • 10 is the default setting. We recommend this setting.
   • To enter a different failure threshold, select the second option and enter the number of failed commands to allow.
   • For all of the members of your cluster to remain online at all times, select Keep all cluster members online at all times.
   • For WHM to notify you when it disables an unresponsive member, select Get a notification when WHM disables an unresponsive cluster member.
2. Click Change.

Disable unresponsive cluster members.

About your DNS cluster configuration

Before you set up your DNS cluster, consider how you will structure it.

How to directly link the web server to the nameservers

You can improve the performance of your servers if you create a cluster setup with direct links between servers. Your severs will function more slowly if there are multiple steps between a web server and a nameserver,

If at all possible, you should link your web server directly to the DNS servers, as shown in the diagram below. This is the ideal DNS setup.

Figure 1. A direct link between the web server and 2 nameservers is optimal.

In this example, webserver.example.com sends DNS information directly to ns1.example.com and ns2.example.com. You can create this setup by using the WHM Configure Cluster feature to link the web server directly to each nameserver (see the instructions below).

Use the primary nameserver as an intermediary

If necessary, place the primary nameserver between the web server and the secondary nameserver. For each intermediate server that you add, the data transfer time will be three times slower than for a direct link.

Figure 2. An intermediate nameserver between the web server and secondary nameserver is acceptable.

To create this configuration, set the web server to sync the primary nameserver, and then set the primary nameserver to sync the secondary nameserver (see the instructions below).

Use multiple intermediary nameservers

The least optimal configuration uses multiple steps between the web server and nameservers. This increases processor load on the servers, as the nameserver software works to update the DNS information on each step. This configuration slows the servers' response time.

Figure 3. If you configure multiple hops between a web server and nameserver, the servers' performance slows.

In this example, for web1.example.com to communicate with ns2.example.com, the information must pass through two intermediary servers, increasing the overall processing load. We do not recommend this method.

Set up the cluster from the web server

To set up your DNS cluster from the web server, follow these steps:

1. Navigate to the Configure Cluster screen. (Home >> Cluster/Remote Access >> Configure Cluster).
   
   
   
   
2. Select the server type from the Backend Type menu in the Add a new server to the cluster section.
   • cPanel & WHM users can use SoftLayer and VPS.NET hosted DNS systems within the WHM interface. To enable DNS Clustering with SoftLayer or VPS.NET, you must obtain an API username and key from SoftLayer or VPS.net, respectively. Once you have done so, choose SoftLayer or VPS.NET from the Backend Type menu.
3. Click Configure. WHM will display the cPanel DNS Remote Configuration screen.
4. Next to Remote cPanel & WHM DNS host, type the hostname or IP address of the nameserver to which you wish to link.
5. Next to Remote server username, type the WHM username for the nameserver (either reseller or root).
6. Under Remote server access hash, enter the nameserver's public remote access key.
   • You can generate and retrieve a public key with the nameserver's WHM interface. Log into WHM on the nameserver, and navigate to Manage SSH Keys. Once the public key appears, paste it into the Remote server access hash box.
     
     
     
     
7. At the bottom of the cPanel & WHM DNS Remote Configuration screen, specify the DNS Role. Next to DNS role, select Standalone, Synchronize changes, or Write-only.
   • The Standalone option is used for DNSONLY servers.
   • The Synchronize changes option causes the web server to synchronize any changes you make on a server throughout the cluster.
   • The Write-only option causes the web server to write DNS data to the nameserver.
   • When you have configured the DNS servers, click Submit to save your settings and return to the Configure Cluster screen.
     Note: We do not recommend that you set up the nameserver to synchronize data to a web server, as this will create extraneous zones on the web server. This means that you do not need to log into WHM on the nameserver and set the web server's DNS role to Synchronize changes.

Set up a reverse trust relationship

1. Select Setup Reverse Trust Relationship for WHM to automatically configure the cluster on the remote server.
   • If you select this option, you will not need to log into the WHM Configure Cluster screen on the remote server. However, you may do so if you wish to modify the remote server's cluster configuration.
   • This option will set the remote server's DNS role to Standalone.
2. Select Debug mode if you wish for WHM to record DNS clustering transactions in the /usr/local/cpanel/logs/error_log file.

The cluster is now set up. When you return to the WHM Configure Cluster screen, the remote server will be listed in the Servers in your DNS Cluster table.

Additional Information

How to delete a server from a DNS cluster

There are several reasons that it may be necessary to delete a server from your DNS cluster. For example, if you need to replace a server that is currently in your DNS cluster, you will need to delete the old server first.

Important: You need to delete a server from a DNS zone before you add a replacement server to the cluster. You cannot have two servers with the same hostname in a DNS cluster.

To remove a DNSONLY server or cPanel server from a DNS cluster, follow these steps:

1. Log into the server you wish to remove from the cluster.
2. Navigate to the Configure Cluster page. (Home >> Cluster/Remote Access >> Configure Cluster).
3. In the Modify Cluster Status box, select Disable DNS Clustering.
4. Click Change.
5. Click Return to Cluster Status.
6. Log into the remaining servers in the cluster.
7. Navigate to the Configure Cluster page. (Home >> Cluster/Remote Access >> Configure Cluster).
8. Locate the server you wish to delete.
9. Click on the X icon under the Actions heading. You will receive the message Server removed from cluster.

When you return to the Configure Cluster screen, the server will no longer appear in the list of servers in the cluster.

If you remove a server from a DNS cluster, the records will no longer synch with the other servers in the cluster. The records on the deleted server will also no longer be present on the servers that remain in the cluster.

How to edit an existing server in a DNS Cluster

You can change a server's DNS role or edit the server's configuration settings at any time.

To change a server's DNS role, follow these steps:

1. Locate the server you wish to edit.
2. In the DNS Role menu, select a new role for the server.
3. Click the ()icon next to the menu to save your changes.

To edit a server's configuration settings, follow these steps:

1. Locate the server you wish to edit.
2. Click the () icon under the Actions heading.
3. WHM will display the cPanel DNS Remote Configuration screen.
4. Once you have made your changes to the server's settings, click Submit.

Note: If you do not see any servers listed at the bottom of the Configure Cluster screen, this means that there are no servers in your DNS cluster.