Hybrid Web Cluster
Hybrid Web Cluster is a software product developed by Hybrid Logic Ltd., a Bristol, United Kingdom based company. The software is designed to provide commodity web hosting in a distributed and fault-tolerant manner on a cluster of either real physical servers or virtual cloud computing infrastructure server instances. Technology. This software splits each website and database into individual units of work - the load generated by each is monitored closely and the cluster automatically and transparently transfers websites and databases between cluster nodes such that no single node is ever overloaded. A single website can go from  having no load at all to requiring its own dedicated web and database servers within seconds. Only one server is ever live for a particular website or database at any one time, enabling existing applications to run un-modified just as they would on commodity shared web hosting. Scalability. The upper bound on the scalability of this system is that no single website can ever utilise more than two servers at once - under this condition all standard LAMP applications will run unmodified. However, it is possible to scale beyond this limit via the use of multi-master database replication - this  requires that applications store all variable state information within a database - the database can then be live on many servers, the web application itself must remain static and can be served from as many nodes in the cluster as required. Redundancy. It is possible to specify a redundancy invariant - this sets the number of machines in the cluster that should hold a copy of each website or database. By default this number is set to 2, this means that under normal operation all data will be held on at least two cluster nodes at any one time. If a cluster  node fails, the system acts to automatically recover its data and resume web hosting within 15 seconds. This is achieved using the filesystem snapshotting capabilities of ZFS. Release. Hybrid Web Cluster began beta testing in September 2010. HybridCluster 2.0 was released on 1 May 2013.