Every system has a limit. Although most providers of web hosting services claim to provide "Unlimited", we all know that any web server has physical limits which is usually hard to scale up, especially without taking the machine offline.
Most IT hosting companies use stand-alone servers to provide website hosting. A very few use any form of HA clusters. Those web hosts that use stand-alone servers do not feature scalability. Every time they need to upgrade the machines they use, major changes to the systems have to be made. Others which that do clustering are more scalable. They would add additional servers to their systems or to remove machines from the set-ups. There are many scenarios and different models of doing clustering. However I'm not the one who would write about them. Plus this is not the purpose of this article.
The reason to start this article at High Scalability is to present Cloud.bg, a cloud hosting service delivered from a Linux based high availability and high scalability system of web servers. It deservers your attention because it is quite unique solution compared to others used in the web hosting service market.
I mean "unique" because Cloud.bg is currently the only Shared Cloud Hosting service that runs the most popular hosting automation software cPanel in a cloud computing environment. It based on a cloud automation platform called Fuscan Linux Cloud, which has been announced in the cPanel forums as "Genuine High Availability, Load-Balanced System for cPanel/WHM".
Does the system feature high scalability?
The system of Cloud.bg connects a number of processing nodes to a shared storage area network. It uses InfiniBand as communication link between all components into the system for high performance. The set-up is based on Red Hat Cluster Suite standards which officially allows a 128 processing nodes to work as a group. I have been told from one of the senior CentOS developers that the cluster can be scaled up to 512 processing nodes, which is really huge. However this information is unofficial and can be proved in theory only.
Cloud.bg runs cPanel/WHM on top of the whole cluster and can be considered as a "Shared Cloud Hosting". All account holders host their websites in a Storage Area Network (SAN) replicated for redundancy. They share resources from many processing nodes. The company guarantees an operational continuity of all the services when a server has to be added, removed, configured or reconfigured in its system. There is no need of OS installation and service configuration on each node.
An interesting feature is that Cloud.bg enables IP load-balancing of cPanel/WHM based web sites. Company's load-balancer automatically detects new IP addresses added in cPanel. The load-balancing runs as a service in the company's infrastructure. It configures the load-balancing for all services running on the customers' websites (IP addresses). In case of failure of any server part of the system, the load-balancer excludes the failed server from the operational group of processing nodes.
The Cloud.bg's system features redundancy on a software level (transparent service failover) and on a hardware level (power, cluster interconnect).
The premier hosting services offered from the company is named sCloud (abbreviation from Shared Cloud). It features 100 GB premium replicated SAN storage, 1,000 GB monthly bandwidth, allows customers to host up to 100 websites and to use the familiar cPanel/WHM interface. Each additional 1 GB of SAN space costs €0.20 ($0.24) and each additional 1 GB of data transfer is priced at €0.03 ($0.036). Cloud.bg also offers Reseller Cloud Hosting.
At the end of this article we have a an answer of the question "How scalable could be a cPanel Hosting service?". It can be scaled up to a cluster of 128 servers. This means a hosting environment ten thousands of high traffic cPanel powered websites.