Yglu: YAML augmented with an expression language
yglu.io
yglu.io
In my experience also, YAML is already too feature-laden for it's own good in this regard, when what people usually want is just a more human-readable JSON.
Using Yglu for config seems like a bad idea (the whole point of config is that it's not code!) - so what is it for?
I've come to the conclusion that helm/templating is awful. Every helm chart I've ever seen suffers from the kitchen sink problem. Dependencies don't really address the problem either, because that's not really resolving a whole lot in the end.
What I've found so far is that Kustomize strikes a solid balance between an off the shelf working config provided from official sources, and making changes myself to suit my environment. Instead of the developer maintaining a kitchen sink approach, they can have something (or a set of somethings) that are straight forward, and I can maintain a set of tweaks that work for me. Unfortunately Kustomize's documentation is not that great, and it is incredibly awkward to work with.
I'm hoping that solid operators come out for most applications instead of helm charts. I'm not 100% sure that they're going to be substantially better than helm, but I'm hoping between operators and kustomize I can link applications together in a way that I get properly maintained applications for minimal effort (ala AWS), without having to maintain a large code base linking all the bits together.
I do think I need to look into pulumi as it might be in the direction I want to go, but I remain skeptical.
Terraform has some good ideas, but is too rigid for kubernetes, and I feel like I'm giving up the flexibility of kubectl. I like the idea of having a state and resolving differences between desired and actual state, but not enough to rewrite everything in HCL.
i authored https://get-kapp.io based on my previous experiences managing iaas resources as cattle. it strongly revolves around idea of managing chnageset between actual and desired configuration.
it was also built as a tool that solely focuses on deployment to k8s, leaving configuration building (ie templating) to other tools.
take a look at it, would love to hear what you think.
on a side note, someone recently asked me to also wrap kapp as a terraform provider: https://github.com/k14s/terraform-provider-k14s
Alas, the ship of toothpaste has sailed out of barn squeezed all over the back of the horse.
We must retreat to Tom's Obvious, Minimal Language[1] and just ventilate anyone trying to throw it into the metaphorical blender.
As for YAML itself, it is handy to have some advanced functionality in a non-turing complete serialization format for the sake of things like security. It's not perfectly analogous, but PostScript is an example of a format that ideally should have been just a descriptive format for the purposes it was intended for, but being Turing complete makes it a security risk
it is based on starlark which is a runtime that does not have facilities to do networking, fs access, etc. building on that, ytt does not allow/provide any kind of non-deterministic operations (access to time, disk, network, random, etc). it expects user to specify explicitly which files to load via -f flag (ie ytt template cannot load random template from fs).
there are several computation attacks that are currently possible (eg infinite loop) but that could be easily addressed thru global timeout for example.
check out interactive playground at https://get-ytt.io
I'm especially interested in jsonnet (https://jsonnet.org/) because of how thoroughly it's documented.
An example that produces three different config files:
local application = 'my-app';
local module = 'uwsgi_module';
local dir = '/var/www';
local permission = 644;
{
'uwsgi.ini': std.manifestIni({
sections: {
uwsgi: {
module: module,
pythonpath: dir,
socket: dir + '/uwsgi.sock',
'chmod-socket': permission,
callable: application,
logto: '/var/log/uwsgi/uwsgi.log',
},
},
}),
'init.sh': |||
#!/bin/bash
mkdir -p %(dir)s
touch %(dir)s/initialized
chmod %(perm)d %(dir)s/initialized
||| % {dir: dir, perm: permission},
'cassandra.conf': std.manifestYamlDoc({
cluster_name: application,
seed_provider: [
{
class_name: 'SimpleSeedProvider',
parameters: [{ seeds: '127.0.0.1' }],
},
],
}),
}Worth reading this if you are considering using it: https://www.arp242.net/yaml-config.html
looks like a very similar effort to ytt: https://get-ytt.io/
it seems like yaql is a different, potentially more limiting, scripting language, but otherwise similar efforts.
However, I am not totally sure that the use of exclamation mark and question mark to start expressions makes it any more readable than embedding code inside comments.
Also not sure what a "single source for template values" means , since in ytt you can have multiple input sources
YTT fulfills its mission, but I wanted to explore a more generic approach and have the loading of libs and values using the same mechanism. Also, allowing the reusable parts to be written in YAML and not only in the additional programming language.
I aim at bringing some ideas in this area and if they make sense, I am happy to see them live, be it in Yglu, YTT or any other tool.
Also, the fact that building Yglu was fast because of YAML parser and YAQL were already existing made me explore on my own, rather than developing these ideas in modifying or coding YTT libs, what I first imagined.
About the readability, I also don't see an argument here. !? vs. #@ does not matter a lot. It only matters that !? is already understood by the YAML parser as a tag, avoiding me to write a parser (I would not have started this work). The cool thing is that tags can also be used in mapping keys.
I will rephrase the "single source for template values" into something that gives better credit, because I really meant that import mechanisms should be the same for values and other stuff (libs, functions, ...). And aslo not only as overlay.
Thanks for the inspiration and let's continue to try and relieve the YAML pain around us.
We have a 1500 line YAML file for our test config because YAML is the one true method for setting up tests. The issues I've run into:
- Indentation errors. Luckily CircleCI has a YAML validator, but the fact that a validator is required isn't great.
- true, false, yes, no. Why?
- date and number coercion vs strings.
- YAML has aliases which in theory let you reuse config. Except you can't compose aliases, like have JavaTest inherit config from GitHubReporter and SlackReporter.
My view is that complex configs should be generated from a reproducible binary, preferable in a real programming language with loops, conditionals, and some form of easy composition. Dhall, jsonnet [2], or Cue [3] are all interesting languages in this space.
[1]: https://dhall-lang.org/ [2]: https://jsonnet.org/ [3]: https://news.ycombinator.com/item?id=20362951