[jwatte]

Continuous deployment means you are never in a state where you cannot deploy. Yes, this requires significant effort. API agility, schema agility, cache agility, ... Lots of things need to be solved! (Imagine storing a serialized cached entity from a later version, abd getting a cache hit in the concurrently operating previous version, for example.)

It's similar to how continuous integration means your master is always stable (all builds work and all tests pass.)

If you can't do a 1% (or 10%) canaried deploy, you're not yet ready for continuous deployment.