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Comment by gorgoiler | Hacker News Reader

If your monorepo compiles to one binary on one host then fine, but what do you do when one webserver runs vN, another runs v(N-1), and half the DB cluster is stuck on v(N-17)?

A monorepo only allows you to reason about the entire product as it should be. The details of how to migrate a live service atomically have little to do with how the codebase migrates atomically.

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That's why I mention having real stable APIs for cross-service interaction, as you can't guarantee that all teams deploy the exact same commit everywhere at once. It is possible but I'd argue that's beyond what a monorepo provides. You can't exactly atomically update your postgres schema and JavaScript backend in one step, regardless of your repo arrangement.

Adding new APIs is always easy. Removing them not so much since other teams may not want to do a new release just to update to your new API schema.

But isn't that a self-inflicted wound then? I mean is there some reason your devs decided not to fix the DB cluster? Or did management tell you "Eh, we have other things we want to prioritize this month/quarter/year?"

This seems like simply not following the rules with having a monorepo, because the DB Cluster is not running the version in the repo.

Maybe the database upgrade from v(N-17) to v(N-16) simply takes a while, and hasn't completed yet? Or the responsible team is looking at it, but it doesn't warrant the whole company to stop shipping?

Being 17 versions behind is an extreme example, but always having everything run the latest version in the repo is impossible, if only because deployments across nodes aren't perfectly synchronised.

This is why you have active/passive setup and you don't run half-deployed code in production. Using API contracts is a weak solution, because eventually you will write a bug. It's simpler to just say "everything is running the same version" and make that happen.

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