Redundancy

High availability is implemented with redundant hardware running redundant instances of each service. If one piece of hardware running one instance of a service fails, the system can then failover to use another instance of a service that is running on hardware that did not fail.

A crucial aspect of high availability is the elimination of single points of failure (SPOFs). A SPOF is an individual piece of equipment or software that causes system downtime or data loss if it fails. In order to eliminate SPOFs, check that mechanisms exist for redundancy of:

  • Network components, such as switches and routers

  • Applications and automatic service migration

  • Storage components

  • Facility services such as power, air conditioning, and fire protection

In the event that a component fails and a back-up system must take on its load, most high availability systems will replace the failed component as quickly as possible to maintain necessary redundancy. This way time spent in a degraded protection state is minimized.

Most high availability systems fail in the event of multiple independent (non-consequential) failures. In this case, most implementations favor protecting data over maintaining availability.

City Cloud is currently available in nine (9) data centers. The sites are:

  • Karlskrona Sweden (2)
  • Stockholm Sweden (2)
  • Frankfurt Germany (1)
  • London UK (1)
  • Tokyo Japan (1)
  • Dubai Emirates (1)
  • Buffalo USA (1)

All data centers are connected with Network connectivity and can be used for redundancy purposes.