isopod VS rules_jsonnet

Tried it[0], worked reasonably well. Be prepared for strong opposition from traditional “devops” folks “who don’t mind yaml” and will drag everyone down.

[0] - https://github.com/cruise-automation/isopod

I like Cue and Jsonnet and Starlark and so on. But all of these have very low mindshare (though Starlark has the most momentum thanks to Bazel), and who knows if they will be dead by next year.

Being an early adopter is difficult both in terms of the immaturity of the tooling — Cue, for example, only has a Go implementation at the moment — and in terms of the risk of betting on an evolutionary dead end, which can cause a lot of unnecessary churn when you want to standardize on something across an entire organization.

As a concrete example, I'd love to replace Kubernetes's use of YAML with something like the above. But the tooling is immature, and almost nobody is using any of it. For example, there's Isopod [1], which is a nice-looking tool to use Starlark with Kubernetes. But it might go the same way as Ksonnet.

[1] https://github.com/cruise-automation/isopod

I can definitely sympathize here - in every context, just straight JSON/YAML configuration seems never expressive enough, but the tooling created in response always seems to come with sharp edges.

Here are some of the things I appreciate about Jsonnet:

- It evals to JSON, so even though the semantics of the language are confusing, it is reasonably easy to eval and iterate on some Jsonnet until it emits what one is expecting - and after that, it's easy to create some validation tests so that regressions don't occur.

- It takes advantage of the fact that JSON is a lowest-common-denominator for many data serialization formats. YAML is technically a superset of JSON, so valid JSON is also valid YAML. Proto3 messages have a canonical JSON representation, so JSON can also adhere to protobuf schemas. This covers most "serialized data structure" use-cases I typically encounter (TOML and HCL are outliers, but many tools that accept those also accept equivalent JSON). This means that with a little bit of build-tool duct-taping, Jsonnet can be used to generate configurations for a wide variety of tooling.

- Jsonnet is itself a superset of JSON - so those more willing to write verbose JSON than learn Jsonnet can still write JSON that someone else can import/use elsewhere. Using Jsonnet does not preclude falling back to JSON.

- The tooling works well - installing the Jsonnet VSCode plugin brings in a code formatter that does an excellent job, and rules_jsonnet[0] provides good bazel integration, if that's your thing.

I'm excited about Jsonnet because now as long as other tool authors decide to consume JSON, I can more easily abstract away their verbosity without writing a purpose-built tool (looking at you, Kubernetes) without resorting to text templating (ahem Helm). Jsonnet might just be my "one JSON-generation language to rule them all"!

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Though if Starlark is your thing, do checkout out skycfg[1]

[0] - https://github.com/bazelbuild/rules_jsonnet

[1] - https://github.com/stripe/skycfg