Helm and Kustomize are absolutely atrocious tools.

The job of these tools is ultimately to generate a bunch of data structures compatible with Kubernetes API schemas. That's it. Take some input, go brrr, and spit out some serialized data structure.

If we replace "YAML" with "JSON", this all seems a bit absurd.

Helm is a tool where you write JSON templates and JSON templating helper functions, then users can provide a values.json file which specifies inputs for the templates and maybe even can contain templated values themselves. But it's easy to get the contents of the values.json slightly wrong in ways that silently fail, so the JSON templates spit out something but it might still be semantically valid Kubernetes JSON. So you can include JSON schema files alongside your JSON templates package to specify the schema of the values.json file, which the tool will check. Then sometimes the values.json file is too verbose to write by hand, so the user chooses another tool (or god forbid writes a small script in a general purpose programming language) to generate their values.json file.

Absurd.

Kustomize is a tool where you give it a bunch of JSON files, or maybe tell it to use one or more of the hellish Helm charts, which is itself a glorified JSON templater. Then you write a JSON configuration file which looks declarative but is secretly somewhat imperative. In this JSON file you specify which transformations you'd like to apply, maybe even specify some inline patches which use the JSON path patch syntax or a strategic merge where you write some more JSON. Some bits of the tool allow you to generate more JSON from files on your disk, like .env files or data files. If the feature set doesn't work you can then use KRM functions as generators or transformers, which allow you to escape from JSON hell and use a general purpose programming language to emit or transform JSON, but the configuration to this KRM function is itself provided as JSON.

Absurd.

These YAML-obsessed tools like Helm and Kustomize purport to be easier because "it's just YAML!" but what you're really doing is writing all of the arguments for a computer program which you must understand, but in YAML. Kustomize is slightly less bad because it doesn't allow for much control flow, but in Helm templates you have control flow, loops, and helper functions. So it's really just a program anyway with a YAML syntax, but you're confined to a stringly-typed templating language.

This exists with tools like Kyverno, too: "oh, the policies are just YAML!" but they introduce a special DSL for writing conditionals, so you're still writing a program anyway, but in a YAML inner platform. If you think of it as "just JSON" then the YAML smokescreen and cargo cult falls away. It then becomes much more tempting to write something specific to your needs in Python, TypeScript, Ruby, Haskell, OCaml, or another general purpose programming language, where you can do whatever it is you need to do without this leaky YAML purism. Kubewarden's scope overlaps a bit with Kyverno, but Kubewarden chooses WASM as the common language instead of YAML.

However, there's an argument to be made about the security model of Helm and Kustomize. Assume that I trust that the authors of those tools are not going to smuggle my data to a malicious third party or install spyware on my computer and that they do not have critical security bugs. Then I can confidently run those tools on my computer with inputs (e.g. charts and kustomizations) that I do not trust. To say nothing of whether the tool will generate a deployment which compromises my cluster when applied.

I think what I'd like to see from the community is tooling that targets Deno or WASM as the common ground. Then I can sufficiently sandbox "packages" like helm charts or kustomizations without worrying that they have general access to my computer or CI/CD runner as if I'd imported a random Python package. I've already started writing something in Deno that tries to emulate Grafana's Tanka in TypeScript. My next job is to write a tool which runs WASM-compiled KRM functions.

But I might need a configuration language for that tool, so maybe I'll choose YAML...