[9dev]

Maybe it’s just me, but these sample workflows don’t look less complicated, just another kind of complex? If you’re already heavily using CUE in your project this lateral complexity shift might make sense, but I don’t see why I would start using it…

[usrme]

Like my guy 'diarrhea' already echoed: using CUE absolutely does not make sense at a small scale; just write your YAML and get on with your day. We were using it to generate dozens upon dozens of GitHub Actions workflows from what was essentially a single source of truth, and because CUE can export to JSON too then that single source of truth could then easily be leveraged to provide other input files to be used elsewhere.

[diarrhea]

> just another kind of complex?

To some extent yes. If all you have is 2 GitHub Actions YAML files you are not going to reap massive benefits.

I'm a big fan of CUE myself. The benefits compound as you need to output more and more artifacts (= YAML config). Think of several k8s manifests, several GitHub Actions files, e.g. for building across several combinations of OSes, settings, etc.

CUE strikes a really nice balance between being primarily data description and not a Turing-complete language (e.g. cdk8s can get arbitrarily complex and abstract), reducing boilerplate (having you spell out the common bits once only, and each non-commit bit once only) and being type-safe (validation at build/export time, with native import of Go types, JSON schema and more).

They recently added an LSP which helps close the gap to other ecosystems. For example, cdk8s being TS means it naturally has fantastic IDE support, which CUE has been lacking in. CUE error messages can also be very verbose and unhelpful.

At work, we generate a couple thousand lines of k8s YAML from ~0.1x of that in CUE. The CUE is commented liberally, and validation imported from native k8s types, and sprinkled in where needed otherwise (e.g. we know for our application the FOO setting needs to be between 5 and 10). The generated YAML is clean, without any indentation and quoting worries. We also generate YAML-in-YAML, i.e. our application takes YAML config, which itself is in an outer k8s YAML ConfigMap. YAML-in-YAML is normally an enormous pain and easy to get wrong. In CUE it's just `yaml.Marshal`.

You get a lot of benefit for a comparatively simple mental model: all your CUE files form just one large document, and for export to YAML it's merged. Any conflicting values and any missing values fail the export. That's it. The mental model of e.g. cdk8s is massively more complex and has unbounded potential for abstraction footguns (being TypeScript). Not to mention CUE is Go and shipped as a single binary; the CUE v0.15.0 you use today will still compile and work 10 years from now.

You can start very simple, with CUE looking not unlike JSON, and add CUE-specific bits from there. You can always rip out the CUE and just keep the generated YAML, or replace CUE with e.g. cdk8s. It's not a one-way door.

The cherry on top are CUE scripts/tasks. In our case we use a CUE script to split the one-large-document (10s of thousands of lines) into separate files, according to some criteria. This is all defined in CUE as well, meaning I can write ~40 lines of CUE (this has a bit of a learning curve) instead of ~200 lines of cursed, buggy bash.