One of the things that I don't like about Nomad is HCL. It is a language that is mainly limited to HashiCorp tools and there's no wider adoption outside at least not to my knowledge.
From the documentation:
> Nomad HCL is parsed in the command line and sent to Nomad in JSON format via the HTTP API.
So why not just JSON or even JSON at all and not MsgPack or just straight up HCL because that's over and over introduced as being machine readable and human friendly both at the same time?
I've only used Terraform, but I absolutely love HCL as a configuration language. I know I'm in the minority about this, but it's so much less fiddly and easier to read than json or yaml. I do wish there were more things that used it.
JSON is fine for serialization, but I hate typing it out. There are too many quotes and commas - all keys and values have to be quoted. The last item in a list or object can't have a trailing comma, which makes re-ordering items a pain. Comments aren't supported (IMO the biggest issue).
YAML is too whitespace dependent. This is fiddly and makes copy-pasting a pain. I'm also not sure how it affects serialization, like if you want to send yaml over the network, do you also have to send all of the whitespace? That sounds like a pain. OTOH I like that quotes are usually optional and that all valid json is also valid YAML. Comments are a godsend.
HCL has the same basic structure of objects and lists, but it's much more user friendly. Keys don't need to be quoted. Commas aren't usually needed unless you compress items onto the same line. It supports functions, list/object comprehensions, interpolations, and variable references which all lead to more powerful and DRY configuration. Granted I'm not sure if these are specific to TF's HCL implementation, but I hope not.
For serialization, HCL doesn't have any advantage over JSON. Sure it's machine-readable but probably much harder to write code that works on HCL specifically than to convert to JSON and use one of the zillions of JSON libraries out there.
JSON was designed for machine readability, HCL was designed for human readability.
HCL requires a lot more code to parse and many more resources to keep in memory vs JSON. I think it completely makes sense to do it this way. K8s is the same. On the server it does everything in JSON. Your YAML gets converted prior to sending to K8s.
To my understanding, you can write most (all?) of the job/config files in JSON if you wish. At my company, we have a ton of HCL files because in the beginning it was easier to hand-write them that way, but we're now getting to the point where we're going to be templating them and going to switch to JSON. In other words, I believe HCL is optional.
From the documentation:
> Nomad HCL is parsed in the command line and sent to Nomad in JSON format via the HTTP API.
So why not just JSON or even JSON at all and not MsgPack or just straight up HCL because that's over and over introduced as being machine readable and human friendly both at the same time?