OTOH, in the context of a distributed system that has to be upgraded live and the deployment of new code has to be carefully staged across hours or days (e.g. a

OTOH, in the context of a distributed system that has to be upgraded live and the deployment of new code has to be carefully staged across hours or days (e.g. a storage cluster with thousands of machines), such mode switches can be absolutely essential. The process can look something like this. * Roll out the code with support for a new feature * Flip the mode switch on a few nodes to use the new feature * Wait a while, watch for anomalies * Enable the new feature on more nodes, until it's on all * Disable support for the old feature (another mode switch) * Eventually, roll out new code with the old feature entirely removed It's not quite a whole-system mode switch as in SoaNM, but that's kind of the point. In a distributed system actions do not affect the whole system all at once, so different rules apply.