A DNS cluster is a group of nameservers that share DNS records, allowing you to physically separate nameservers handling DNS requests from your web servers. This distributed setup improves redundancy, performance, and fault tolerance for domain name resolution across your hosting infrastructure.
At OBHost, DNS clustering is available through WHM (Web Host Manager) and allows you to configure multiple servers to work together, automatically synchronizing DNS zone changes across all cluster members for enhanced reliability.
What Is a DNS Cluster?
A DNS cluster consists of multiple nameservers that automatically replicate DNS zone data among themselves. When you make a DNS change on one server in the cluster, that change propagates to all other cluster members automatically. This ensures consistency across your DNS infrastructure and provides backup nameservers if one becomes unavailable.
The primary benefits include:
- Improved redundancy through multiple nameservers
- Better performance by distributing DNS query load
- Automatic synchronization of DNS records across servers
- Geographic distribution of nameservers for faster resolution
- Continued DNS service even if individual servers fail
How DNS Clustering Works
When you configure a DNS cluster, you designate one or more servers as cluster members. These servers communicate with each other to share DNS zone information. Whenever a DNS record is created, modified, or deleted on any cluster member, that change is automatically pushed to all other members in the cluster.
This synchronization happens through secure communication between the servers, ensuring that all nameservers in your cluster always have identical, up-to-date DNS records for your domains.
Setting Up DNS Clustering
To configure DNS clustering in WHM, you need root or reseller access with the appropriate DNS Clustering ACL (Access Control List) privilege. The setup process involves enabling DNS clustering globally and then adding individual servers to your cluster.
Enabling DNS Clustering
Navigate to the DNS Cluster interface in WHM. You'll find options under Global Cluster Options to enable or disable DNS clustering:
- Click Enable DNS clustering to activate the feature
- Click Disable DNS clustering to deactivate the feature
Once enabled, you can begin adding cluster members and configuring synchronization settings.
Adding Servers to Your Cluster
After enabling DNS clustering, you can add remote servers as cluster members. Each server you add must be accessible and properly configured to participate in the cluster. The servers will then begin sharing DNS zone data automatically.
Users with full administrative privileges can add custom DNS servers to a cluster and modify existing cluster member settings.
Important DNSSEC Considerations
If you use DNSSEC (DNS Security Extensions) for any domains in your cluster, all servers in that cluster must run PowerDNS. This is a strict requirement because DNSSEC relies on cryptographic signatures that must be consistent across all nameservers.
Mixed DNS server software (such as combining PowerDNS and BIND servers) is not supported when DNSSEC is enabled on any domain in the cluster. Ensure all cluster members use PowerDNS before enabling DNSSEC on your domains.
Managing Cluster Members
The DNS Cluster interface allows you to manage your cluster as either the root user or as a reseller. Select your role from the Managing DNS Cluster as menu before making changes.
Before adding custom DNS servers or modifying existing cluster members, ensure you're managing the cluster as the root user, as these operations require full administrative privileges.
Failure Threshold Configuration
The Failure threshold for cluster members setting determines how many failed communication attempts are allowed before WHM automatically disables an unresponsive cluster member. This helps maintain cluster performance by removing servers that aren't responding properly.
Setting an appropriate failure threshold prevents your cluster from repeatedly attempting to sync with offline or malfunctioning servers, which could slow down DNS updates across your infrastructure.
Reseller Access and Permissions
Resellers must have the DNS Clustering ACL privilege to view and use the DNS Clustering section in WHM. This privilege is granted by the server administrator and controls whether resellers can manage DNS clusters for their accounts.
If you're a reseller and don't see DNS clustering options, contact your hosting provider to request the necessary permissions.
Best Practices for DNS Clusters
To get the most from your DNS cluster configuration:
- Use at least two cluster members for basic redundancy
- Distribute cluster members across different data centers or geographic locations
- Monitor cluster member status regularly to identify and address synchronization issues
- Set an appropriate failure threshold (typically 3-5 attempts) to balance responsiveness and stability
- Ensure all cluster members run the same DNS server software, especially when using DNSSEC
- Keep all cluster members updated with the latest software versions
Frequently Asked Questions
What happens if one server in my DNS cluster goes offline?
When a cluster member goes offline, the remaining servers continue to handle DNS queries normally. Your domains remain accessible because multiple nameservers are still available. The offline server will automatically resynchronize with the cluster when it comes back online.
Can I mix different DNS server software in one cluster?
You can only mix DNS server software if none of your domains use DNSSEC. If any domain in the cluster uses DNSSEC, all cluster members must run PowerDNS. For consistency and compatibility, it's generally recommended to use the same DNS server software across all cluster members.
How long does it take for DNS changes to propagate across cluster members?
DNS changes typically propagate to all cluster members within seconds to a few minutes. The actual synchronization time depends on network conditions between your servers and the size of the zone being updated. However, remember that DNS changes may still take longer to propagate globally due to TTL (Time To Live) settings and caching by ISPs and resolvers.
Do I need special ports open for DNS clustering to work?
Yes, cluster members need to communicate with each other over specific ports. Ensure your firewall allows traffic between cluster members on the necessary ports for DNS synchronization. Your server administrator or OBHost support can provide specific port requirements for your configuration.
For assistance with DNS cluster setup or troubleshooting, OBHost's support team is available 24/7. Visit our contact page or email support@obhost.org for expert help with your DNS configuration.
