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This is the story of how the Launchpad (https://launchpad.net) development team switched to a continuous integration system to increase several flows in their development process: flow of changes on trunk; flow of changes requiring database schema upgrade; flow of deployed changes to end users. The switch to a buildbot based system meant violating a very old company taboo: a trunk that doesn't pass its test suite. The risk of a broken trunk was offset by allowing each developer to run the full test suite in the Amazon EC2 cloud.
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Francis J. Lacoste (2009) studied this question.