---
title: "Hut"
description: "Control node"
date: 2023-06-13T19:36:57+02:00
---

![Hut](hut.jpg)

From the hut we monitor and control other nodes. It consist of one node only,
which is available at `hut` or `xeon07`. It runs the following services:

- Prometheus: to store the monitoring data.
- Grafana: to plot the data in the web browser.
- Slurmctld: to manage the SLURM nodes.
- Gitlab runner: to run CI jobs from Gitlab.
- Nix binary cache: to serve cached nix builds

This node is prone to interruptions from all the services it runs, so it is not
a good candidate for low noise executions.

# Binary cache

We provide a binary cache in `hut`, with the aim of avoiding unnecessary
recompilation of packages.

The cache should contain common packages from bsckpkgs, but we don't provide
any guarantee that of what will be available in the cache, or for how long.
We recommend following the latest version of the `jungle` flake to avoid cache
misses.

## Usage

### From NixOS

In NixOS, we can add the cache through the `nix.settings` option, which will
enable it for all builds in the system.

```nix
{ ... }: {
  nix.settings = {
    substituters = [ "https://jungle.bsc.es" ];
    trusted-public-keys = [ "jungle.bsc.es:pEc7MlAT0HEwLQYPtpkPLwRsGf80ZI26aj29zMw/HH0=" ];
  };
}
```

### Interactively

The cache can also be specified in a per-command basis through the flags
`--substituters` and `--trusted-public-keys`:

```sh
nix build --substituters "https://jungle.bsc.es/cache" --trusted-public-keys "jungle.bsc.es:pEc7MlAT0HEwLQYPtpkPLwRsGf80ZI26aj29zMw/HH0=" <...>
```

### Nix configuration file (non-nixos)

If using nix outside of NixOS, you'll have to update `nix.conf`

```bash
echo "substituters = https://jungle.bsc.es" >> /etc/nix/nix.conf
echo "trusted-public-keys = jungle.bsc.es:pEc7MlAT0HEwLQYPtpkPLwRsGf80ZI26aj29zMw/HH0=" >> /etc/nix/nix.conf
```

### Hint in flakes

By adding the configuration below to a `flake.nix`, when someone uses the flake,
`nix` will interactively ask to trust and use the provided binary cache:

```nix
{
  nixConfig = {
    extra-substituters = [
      "https://jungle.bsc.es/cache"
    ];
    extra-trusted-public-keys = [
      "jungle.bsc.es:pEc7MlAT0HEwLQYPtpkPLwRsGf80ZI26aj29zMw/HH0="
    ];
  };
  outputs = { ... }: {
    ...
  };
}
```