MetaMorphMagi: From Offline to Online Software Upgrades in Large-Scale IT Infrastructures

Software upgrades are one of the leading causes of downtime in IT infrastructures. Long running datamigration processes require intensive up-front preparation, extended maintenance windows and close monitoring, and they impose a significant burden on the system administrators. Even worse, major upgrades sometimes fail due to complex, hidden dependencies within the system, causing unplanned downtime and loss of critical data. In this paper, we propose a technique for converting an offline data-migration process into a dependency-agnostic online upgrade that requires minimal administrative intervention and that eliminates the need for planned downtime. We illustrate our technique by walking the reader through a hypothetical, but realistic online upgrade scenario in a medium-sized IT infrastructure – namely, hot-swapping the wiki software that underlies Wikipedia with an entirely different wiki engine.