hydra post

content/posts/nixos-hydra-ci.md

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++++
+title = "Welcome to Hydra"
+date = 2025-05-17
+draft = false
+
+[taxonomies]
+categories = [ "nixos" ]
+tags = [ "nixos", "nixos-25.05" ]
++++
+
+## CB (Continuous Build system)
+
+This is what [NixOS](https://hydra.nixos.org/) itself uses for building packages for it's [channels](https://nixos.wiki/wiki/Nix_channels). Setting it up yourself on NixOS is pretty easy with this nix config:
+
+```nix
+{ config, pkgs, lib, ... }:
+
+{
+  services.hydra = {
+    enable = true;
+    hydraURL = "localhost:3000";
+    buildMachinesFiles = [ ];
+    notificationSender = "hydra@localhost";
+    useSubstitutes = true;
+  };
+}
+```
+
+once you add that to your `configuration.nix` (or another nix file that you import) and rebuild you'll find it running on port 3000 (localhost:3000). For creating a project and other admin roles I would recommand looking at [this page](https://nixos.wiki/wiki/Hydra).
+
+### Your own nixpkgs
+
+I started my own [nixpkgs repository](https://gitlab.com/ahoneybun-nix/nixpkgs) recently and this is my flake:
+
+```nix
+{
+  description = "Aaron Honeycutt's packages";
+
+  inputs = {
+    nixpkgs.url = "nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = {
+    self,
+    nixpkgs,
+    flake-utils,
+    ...
+  }:
+    flake-utils.lib.eachSystem ["x86_64-linux" "aarch64-linux"] (
+      system: let
+        pkgs = import nixpkgs {
+          inherit system;
+          config.allowUnfree = true;
+          overlays = [
+            (import ./pkgs)
+          ];
+        };
+
+      in {
+        packages = (import ./pkgs {}) pkgs;
+
+        hydraJobs = (import ./pkgs {}) pkgs;
+      }
+    );
+}
+```
+
+With this you can run `nix build .#honeyfetch` (one of the packages in that repository) to build it for the host architecture. Now the part for Hydra itself is `HydraJobs` so that Hydra will pick up those packages and build them:
+
+{{ figure(src="/images/nixos-hydra-ci/built-x86-64-linux.png", alt="Hydra building for x86_64-linux", caption="Hydra building for x86_64-linux") }}
+
+## Building for other architectures
+
+NixOS is great at supporting 4 main architectures (known as Platforms):
+
+- x86_64-linux
+- aarch64-linux
+- x86_64-darwin
+- aarch64-darwin
+
+there is a 5th one which is i686-linux though it is not as common.
+
+Hydra can build for all of them and this example we'll add aarch64-linux (for devices such as the Raspberry Pi in my case), this is how our Hydra configuration looks with that enabled:
+
+```nix
+{ config, pkgs, lib, ... }:
+
+{
+  services.hydra = {
+    enable = true;
+    hydraURL = "localhost:3000";
+    buildMachinesFiles = [ "/etc/nix/machines" ];
+    notificationSender = "hydra@localhost";
+    useSubstitutes = true;
+  };
+
+  nix.buildMachines = [
+    {
+      hostName = "localhost";
+      protocol = null;
+#      system = "x86_64-linux";
+      systems = [ "x86_64-linux" "aarch64-linux" ];
+      supportedFeatures = ["kvm" "nixos-test" "big-parallel" "benchmark"];
+      maxJobs = 8;
+    }
+  ];
+}
+```
+
+If you just want to build for x86_64-linux or a certain Platform only you can use the `system` variable instead of the `systems` one. If you use both the `system` one will override everything so only that one will be used. Once the change is made simply rebuild your configuration with `sudo nixos-rebuild` and you should see this, it is important to note that building on a non-native Platform will take a while. 
+
+{{ figure(src="/images/nixos-hydra-ci/built-systems.png", alt="Hydra building for x86_64-linux and aarch64-linux", caption="Hydra building for x86_64-linux and aarch64-linux") }}
+