Curious to know how many people do zero-downtime deployment of backend code and how many people regularly take their service down, even if very briefly, to roll out new code.
Zero-downtime deployment is valuable in some applications and a complete waste of effort in others, of course, but that doesn’t mean people do it when they should and skip it when it’s not useful.
You don’t need to wiry about mixed version environments but you need to worry about whether you can roll back your changes without loss of data. It’s not as hard but it seems to get overlooked if there haven’t been any bad deployments lately.