> Does it? Reverting a bad deploy is not only about running the previous version.

It does. We’ve tried. No it’s not as easy as running the previous version.

I have written about this: https://swizec.com/blog/why-software-only-moves-forward/

I read the article and to be honest I don't know where we disagree. I disagree with this quote,

> Takes ~10min to revert a bad deploy

A bad deploy can take way over that just in customer or partner management communication.

Having data model changes be a part of regular deployments would give me persistent heartburn.

It's why you always have a rollback plan. Every `up` needs to a `down`.

If you do that, it expands your test matrix quadratically.

So, it makes sense if you have infinite testing budgets.

Personally, I prefer exhaustively testing the upgrade path, and investing in reducing the time it takes to push out a hot fix. Chicken bits are also good.

I haven’t heard of any real world situations where supporting downgrades of persistent formats led to best of class product stability.

Would love to hear of an example.

Aircraft engineer: “That’s why you have parachutes.”

They might be an appropriate safeguard for a prototyping shop, but not for Delta.