nix-weather/README.md
Christina Sørensen 756eb7ae13
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Signed-off-by: Christina Sørensen <christina@cafkafk.com>
2024-09-05 10:11:53 +02:00

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SPDX-License-Identifier: EUPL-1.2
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# Nix Weather - Check Cache Availablility of NixOS Configurations
A *fast* rust tool to check availability of your entire system in caches. It so
to speak "checks the weather" before going to update. Heavily inspired by [`guix
weather`](https://guix.gnu.org/manual/en/html_node/Invoking-guix-weather.html).
[![Built with Nix](https://img.shields.io/badge/Built_With-Nix-5277C3.svg?logo=nixos&labelColor=73C3D5)](https://nixos.org)
[![Contributor Covenant](https://img.shields.io/badge/Contributor%20Covenant-2.1-4baaaa.svg)](CODE_OF_CONDUCT.md)
[![REUSE status](https://api.reuse.software/badge/git.fsfe.org/reuse/api)](https://api.reuse.software/info/git.fsfe.org/reuse/api)
[![License: EUPL-1.2](https://img.shields.io/badge/licence-EUPL--1.2-blue)](https://commission.europa.eu/content/european-union-public-licence_en)
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## Usage
> **Note**
> Currently, `nix-weather` only has first-class support for flakes.
General usage would be like this:
```bash
nix-weather --name myhost --config ~/git/my-nixos-config
```
Here, we specify the name of the host, as specified at the flake output
`nixosConfiguration`, and a path to the NixOS configuration flake.
## How It Works
The basic idea is that we construct a set of all requisites to build the
top-level of a NixOS configuration, and then query Nix cache(s) for the narinfo.
By doing this in a high concurrency, parallel task runner (i.e. tokio async
runtime), and only querying the headers for status codes, we can reach
impressive speeds, typically around 45~ network time.
One of the biggest limiting factors regarding speed is building the
`config.system.toplevel`, and finding the necessary requisites with `nix-store`.
Caching the requisites is a future goal, so that we only have to build the
`toplevel`, and then match against its derivation in cache, which should cut
down the nix part of the runtime by ~80%.
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## Contributing
For information on contributing, please see [CONTRIBUTING.md](CONTRIBUTING.md).