Re: Are declarative app configs worth it?

[Murad Mamedov]

Hi,

I was adding to guix fail2ban, greetd services with their 
configurations
and pending configuration for connman. Basically the overall idea 
behind
guix (i.e. having declarative configuration) is really nice. 
Having such
mechanism powered by general purpose language like scheme is 
another
very nice. In the ideal world, where all configurations are 
provided and
ported to guix with included documentation whould be beautiful 
from user
perspective.

However, we are not in an ideal world. From what I see, these 
problems
araise from three main sources:

- Programs they selves. For instance if every program would follow 
 let's
 say something like 12-factor app, then such programs would have 
 very
 clear purpose, and thus clear configuration. One of such good 
 examples
 in my practice would be greetd. Worst example would be fail2ban, 
 where
 half of program logic is expressed in the configuration, very 
 ugly
 very bad. Users have hard time to understand how it is 
 configured
 in plain, porting such mechanism to another dsl, whole another 
 level
 of pain. Rarely programs demand complex configuration, as some 
 one
 noted, there is already a conventional mechanism to add 
 `extra-config`
 field or having `plain-config-file-like` option saves the day.

- Porters of programs and services to guix. Such person should not
 blindly port the configuration to the guix, but clearly 
 understand
 how close or far away program from let's say 12-factor app (if 
 we
 take it as reference). If very close, providing detailed strict
 configuration records is a bliss. If very far, porter have to
 think and add `extra-config` and `plain-config-file-like` 
 options.

- Users of guix have to understand, that what they write in scheme
 for guix is not a configuration but a program. Once you trully
 understand that, as a user you may change your behavior to have
 configurations stored in the variables instead of inlining them
 within service configuration. Then they can be used in service,
 or manualy serialized to a file. Or even, one might write a 
 program
 to traverse services and/or operating-system and to serialize
 configuration on disk for LFS-like or systemd-like 
 compatibility.

IMHO, separating configuration (applications) from configuration 
(guix
applications?) is not very wise way and will defeat very idea of
having single, programming language based declarative 
configuration.

What we need is more tooling around configuration and 
documentation,
for instance:
- tool to extract documentation from man pages
- tool to "copy-paste" configuration documentation into guix.texi
- tool to cross link packages, configuration documentations
- code completion with documentation hinting in writing guix 
 scheme
- etc.

Thanks in advance,
muradm

Sergey Trofimov <sarg@sarg.org.ru> writes:

> Hi guix,
>
> I want to start a discussion around how to manage user app 
> config
> files.
> Copying my message from https://issues.guix.gnu.org/68010, where
> home-zathura-configuration with 76 fields is proposed.
>
> I have mixed feelings about pulling 3rd-party software 
> configurations
> in guix:
> - adding it to guix increases maintenance burden: new versions 
> could
>  add or remove config options
> - it requires documentation/translation, another hidden cost
> - it bloats guix: imagine if we add configs for every
>   user-configurable app
> - such configs are not easily transferrable: if I were to use 
> the
>   same app in non-guix env, I'd have to maintain 2 configs
>
> Another recent example is `oci-container-configuration` which 
> defines
> a subset of docker-cli startup arguments. The problem is that 
> `docker
> run` command has 96 options and the configuration only uses a 
> handful,
> lacking a way to provide the remaining ones.
>
> I think guix should not embed config generators for user 
> software. The
> only need I see for such generators is when there are options 
> which
> should be the same among multiple applications (e.g. color 
> schemes or
> shared directories). For such usecase guix should provide better 
> text
> manipulation tools which home owners could use to parameterise
> configs.
>
> Best regards,
> Sergey Trofimov