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Yglu: YAML augmented with an expression language

yglu.io

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Re: Yglu: YAML augmented with an expression language

#21

Post by sa46 »

techntoke wrote: post #16

People that hate YAML must also dislike Markdown.

I despise YAML but like Markdown. They serve different purposes. Markdown is a light-weight way to format prose. YAML is a config language. Markdown is pretty good at formatting prose. YAML is a disaster confusing syntax unsuitable for configs past about 100 lines.

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

Re: Yglu: YAML augmented with an expression language

#22

Post by pavon »

dpc_pw wrote: post #18

http://memecrunch.com/meme/2HKTR/no-god-please-no/image.png

Compared to Helm and other common kubernetes templating solutions that try to use blind textual replacement in whitespace-sensitive language, this (or something like it) looks like a god-send.

Re: Yglu: YAML augmented with an expression language

#23

Post by nkaviani »

nkaviani wrote: post #20

one of the ytt authors here. 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.

actually glanced over the blog post. so this is inspired by ytt, which is pretty cool.

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

Re: Yglu: YAML augmented with an expression language

#24

Post by techntoke »

moderation wrote: post #19
techntoke wrote: post #16

People that hate YAML must also dislike Markdown.

Compare the YAML spec [0] to the Markdown spec [1] 0. https://yaml.org/spec/1.2/spec.html 1. https://daringfireball.net/projects/markdown/index.text

The link you listed for Markdown isn't the spec. Here is a more official spec:

https://spec.commonmark.org/0.29/

Re: Yglu: YAML augmented with an expression language

#25

Post by smitty1e »

throwaway894345 wrote: post #5
fredley wrote: post #2

What is this for? YAML in my experience is used for writing and maintaining config at some supposed sweet-spot between human-readable and machine-readable structure. 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!) -…

For large, repetitive configurations (Kubernetes configs, CloudFormation templates, CI job configurations, etc) you often want ways to abstract and/or DRY your configurations. Kubernetes folks use mustache/jinja/Go templates via Helm, which is a real mess. CloudFormation builds its own (shitty) evaluation language on top of YAML. This presumably aims to improve on those sort of hacky solutions. I feel strongly that t…

> This presumably aims to improve on those sort of hacky solutions.

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.

[1] https://github.com/toml-lang/toml

Re: Yglu: YAML augmented with an expression language

#26

Post by iudqnolq »

Some competing languages: https://news.ycombinator.com/item?id=20357079

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' }],
          },
        ],
      }),
    }

Re: Yglu: YAML augmented with an expression language

#27

Post by mv1 »

Hold on. YAML gained popularity as a nice syntax for JSON, which itself was a subset of JavaScript, a full programming language. Now, we are adding some computational capabilities back to YAML? Wouldn't it be better to just execute JavaScript to generate a JSON object and skip building a new language inside of YAML?

Re: Yglu: YAML augmented with an expression language

#28

Post by lbovet »

nkaviani wrote: post #23
nkaviani wrote: post #20

one of the ytt authors here. 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.

actually glanced over the blog post. so this is inspired by ytt, which is pretty cool. 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

Yes, I liked the idea of ytt and after playing a bit, I felt that we could do YAML processing in some more YAML-native way.

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.

Re: Yglu: YAML augmented with an expression language

#29

Post by cppforlife »

escardin wrote: post #13
throwaway894345 wrote: post #5

Earlier quoted context omitted.

For large, repetitive configurations (Kubernetes configs, CloudFormation templates, CI job configurations, etc) you often want ways to abstract and/or DRY your configurations. Kubernetes folks use mustache/jinja/Go templates via Helm, which is a real mess. CloudFormation builds its own (shitty) evaluation language on top of YAML. This presumably aims to improve on those sort of hacky solutions. I feel strongly that t…

That's what I've been finding a lot lately. Kubenetes manifests have very complete schemas, but there's not really any official concise way to express them or relations between them. 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 th…

> 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

Re: Yglu: YAML augmented with an expression language

#30

Post by cppforlife »

bitbang wrote: post #11
fredley wrote: post #2

What is this for? YAML in my experience is used for writing and maintaining config at some supposed sweet-spot between human-readable and machine-readable structure. 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!) -…

Automated config management. 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

https://get-ytt.io (i am one of the authors), one of the tools that inspired yglu, has been designed from ground up with an eye towards security even though its turing complete.

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

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