I've never thought having the environment in the version tag (or whatever resembles that) was a good idea. It is a remarkably common thing, though.

But it means that, by definition, we are deploying a different tag to dev, staging, and prod. (Or whatever your pre-prod envs are called.) Hopefully, these all point at the same commit … hopefully¹. (Worse, some schemes out there — not the TFA's — force them to never specify the same commit(!) and we devolve to "let's pray those different commits specify the same tree.)

Just tag a version number. Use the date, if you can't think of a version number. Separately, you maintain some file containing what tag/revision you want on each of your dev/stage/prod/etc. environments. This is basically the same rough scheme as what TFA lays out … but not special. Just text files, in a repo², like everything else. You can do it in a separate repository (I'd recommend) or the same one (I wouldn't recommend, but it can work).

The exemplar question,

> When did we last deploy the www.our-app app to production?

Is just the `git log` of the file that contains the hash that that app should be deployed to.

The SRE in me notes, however, that gitops-based deployments (what all of these schemes are) represent the point in time that a deployment is requested — not when it actually rolls out. Deploys that fail or are blocked on some externality can converge much much later than the git commit instructing them to occur is minted. Also, the SRE in me wants to notes that deploys in any realistic scenario are not a point in time. (It starts when you start bringing up the first replica of your app, and it finishes when the last replica of the older deployment has spun down. Depending on how much bloat you have … it can be a good little span of time.)

(¹TFA's scheme seems to contain a textual reference to the tree sha, but is that checked?)

²If you have worked with Flux or ArgoCD, you're almost certainly doing exactly what I am describing, though those are not the only two such systems capable of it.