Showing posts from January, 2012

To Be (HA) or Not to Be

Or, what does it really mean to be highly available in the cloud Good IT practices try to maximize SLA conformance, especially around availability. Lessons learned from a disk failure in the Exchange server leading to mail outages and the inevitable fire drills have been deeply embedded into minds. REDUNDANCY EVERYWHERE. power supplies, network connections, disks - if you can put 2 of them suckers in there, you do. Just to keep that machine running. That machine should never fail. The web has mitigated things somewhat. Rather than a relying on hardware redundancy (where you don't use half your equipment), deployment strategies have evolved. A large pool of web servers can sustain SLA's with some servers failing by utilizing load-balancers to only direct traffic to live web servers. This scheme brings with it worries about session state availability and other share information (e.g database) but nonetheless its progress. Since hardware is now allowed to fail, software devel