Add instructions on how to use the cache in the web

web/content/cache/_index.md

@@ -0,0 +1,68 @@
+---
+title: "Cache"
+description: "nix binary cache"
+date: 2025-02-26T17:37:19+0100
+---
+
+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 = { ... }: {
+    ...
+  };
+}
+```

web/content/hut/_index.md

@@ -13,6 +13,7 @@ which is available at `hut` or `xeon07`. It runs the following services:
 - 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 (See [cache](/cache))
 
 This node is prone to interruptions from all the services it runs, so it is not
 a good candidate for low noise executions.