Monday, October 10, 2011

Cloud 9? Don’t forget data replication strategies

It is still important to decide on your data, server replication strategy when you deploy your core business services and data assets to an internal, external or hybrid cloud models.

Understanding the implications of Active Replication, Passive Replication, Hot Backup, Warm Backup, Cold Backup, State Change Synchronization, Load Balancing and Fault Tolerance are key to making essential choices for a solid deployment architecture on the cloud.

Elasticity, capacity flexibility, horizontal and vertical scalability and dynamic resource allocation makes life a lot easy on the cloud.

Active replication is not achieved by taking cold backups, state changes are not logged for periodic flushes to the replicas, state is not synchronized to only support backup replica when the primary fails. Instead each replica is identical, each replica attempts to process each request – an interceptor takes care of idem potency between replicas. If you want a Primary Service to support all incoming requests, and periodically synchronize its state with the replicas – what you have is a Warm Backup or Passive Replication.

Take a hot backup during times when you have low scalability needs on the RDBMS systems, whereas a cold backup should be reserved for “Sundays” or in the 70s. If you’re going to support the cloud – forger cold backups and start thinking CA (Continuous Availability).