cPanel multi server aka cPanel cluster – How it helps your webhosting business

Many see cPanel multi server (aka cPanel cluster) as a way to prevent business downtime. The logic goes that even if one server fails, the other servers can keep websites and mail online. But, how true is that?

In our role as Hosting support specialists for web hosting companies, Bobcares engineers manage hundreds of cPanel servers. We setup and manage several cPanel cluster infrastructure as a part of this cPanel server management services.

From this experience, we could see that though cPanel clusters cannot totally prevent a business downtime, they be used to minimize the impact of a downtime, and to simplify server administration.

cPanel multi-server cluster – Do you need it?

As of version 11.56, cPanel offers DNS Cluster for DNS high availability and Configuration Cluster for easier server management. If you already have cPanel servers, here’s how cPanel clusters can help you:

1. DNS cluster – How we configure them to prevent service downtime

cPanel creates 2 name servers for each website created in a server (say, ns1.website.com and ns2.website.com). By default, both these two name servers are created in the same physical machine.

This poses a couple of issues:

  • In the event of a server crash, DNS will stop working. This brings down both website and mail – even if the mail is hosted elsewhere (like Google Apps).
  • If a website needs to be moved to another server due to resource constraints or other reasons, the name servers need to be changed, leading to extensive downtime.

 

NS failure blocking backup MX access - cPanel multi-server cluster

DNS failure affecting mail services

 

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To prevent such downtime, we setup central DNS clusters for our customers. The DNS of all websites would be hosted in 2 or more dedicated DNS servers.

This way every website will have the same set of name servers (eg., ns1.webhostingcompany.com, ns2.webhostingcompany.com), and even if one server fails, other servers will ensure that the services are up.

With these DNS clusters, we’ve been able to:

  • Prevent mail bounces using a secondary MX entry for domains, that routes mails to a backup mail server.
  • Avoid web or mail downtime during website migrations to other servers. Since name servers are the same for all domains, there’s no need for complex DNS changes and prevents associated downtime.
  • Reduce customer complaints and support tickets that happen during domain migrations.

 

NS cluster directs mail to backup MX - cPanel multi-server cluster

How DNS cluster ensures service uptime

 

Many of the name server clusters we’ve implemented were based on open source BIND servers. cPanel has a similar solution called DNSONLY. With this, cPanel servers can be setup to store DNS records in a remote DNSONLY cluster.

See how we add value to your business!

When we setup DNSONLY clusters, we maximize the cluster effectiveness and security by:

  • Setting up the name servers in separate geographical locations – This ensures that a network issue won’t bring down both servers.
  • Making all name servers “masters” – This helps to lower DNS update delays. When a DNS record changes, all name servers in the cluster are updated at the same time. This avoids propagation delay among name servers.
  • Securing the cluster against cache poisoning, and other attacks – An attack on the cluster can bring down all websites. We prevent it through a series of DNS security tweaks.
cPanel DNSONLY cluster - common pitfalls

cPanel DNSONLY cluster

 


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2 Comments

  1. Great article. I am assuming your clustering is focused on clustering servers within one data center? But what about high availability in the event of a data center issue or Internet network outage at a point close to the data center?

    Seems like you would need some sort of floating IP setup so when one server goes down it routes to the server at the other data center.

    The simple solution would be to just host with someone like Google Cloud Services and let them take care of the high availability. But what if you are a DIY person not hosting anything very high traffic and trying to keep ongoing hosting costs to a minimum?

    Seems like you would need two separate WHM/Cpanel setups but with different IPs and then you would need realtime replication of the changing data (MySQL, Email, and Website files). What is the viable solution with least chance of headaches?

    Reply
    • Hi Jeff,

      Yes, that’s right, the article is about clustering in one datacenter.

      Multi-datacenter HA systems can be tricky because data synching over the internet can be unreliable.

      IF you get into an agreement with a multi-NOC provider like Softlayer, a private channel can be setup to get comparatively reliable data synching. Then IP switching can be enabled by renting a BGP router. But such a solution will be pretty complex and cost prohibitive for an average web host. I’m assuming you are talking about web hosting because cPanel is focused on web hosting.

      However, if you have apps to host, AWS has out-of-the-box high availability zones. I’d rather use a PaaS solution like Elastic Beanstalk, OpenShift or some other cloud enabled auto-scalable PaaS services. In such a case, you are shielded from the background complexities.

      Again, all of this depends on how much control you want over your infrastructure and your budget.

      Reply

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