refactor(ops): Split //ops/nixos into different locations r/2482

Splits //ops/nixos into:

* //ops/nixos.nix - utility functions for building systems
* //ops/machines - shared machine definitions (read by readTree)
* //ops/modules - shared NixOS modules (skipped by readTree)

This simplifies working with the configuration fixpoint in whitby, and
is overall a bit more in line with how NixOS systems in user folders
currently work.

Change-Id: I1322ec5cc76c0207c099c05d44828a3df0b3ffc1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2931
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
Reviewed-by: glittershark <grfn@gws.fyi>

1 files changed, 48 insertions, 0 deletions

diff --git a/ops/modules/tvl-buildkite.nix b/ops/modules/tvl-buildkite.nix
new file mode 100644
index 0000000000..2aa3b81811
--- /dev/null
+++ b/ops/modules/tvl-buildkite.nix
@@ -0,0 +1,48 @@
+# Configuration for the TVL buildkite agents.
+{ config, depot, pkgs, lib, ... }:
+
+let
+  cfg = config.services.depot.buildkite;
+  agents = lib.range 1 cfg.agentCount;
+  description = "Buildkite agents for TVL";
+
+  # All Buildkite hooks are actually besadii, but it's being invoked
+  # with different names.
+  buildkiteHooks = pkgs.runCommandNoCC "buildkite-hooks" {} ''
+    mkdir -p $out/bin
+    ln -s ${depot.ops.besadii}/bin/besadii $out/bin/post-command
+  '';
+in {
+  options.services.depot.buildkite = {
+    enable = lib.mkEnableOption description;
+    agentCount = lib.mkOption {
+      type = lib.types.int;
+      description = "Number of Buildkite agents to launch";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    # Run the Buildkite agents using the default upstream module.
+    services.buildkite-agents = builtins.listToAttrs (map (n: rec {
+      name = "whitby-${toString n}";
+      value = {
+        inherit name;
+        enable = true;
+        tokenPath = "/etc/secrets/buildkite-agent-token";
+        hooks.post-command = "${buildkiteHooks}/bin/post-command";
+      };
+    }) agents);
+
+    # Set up a group for all Buildkite agent users
+    users = {
+      groups.buildkite-agents = {};
+      users = builtins.listToAttrs (map (n: rec {
+        name = "buildkite-agent-whitby-${toString n}";
+        value = {
+          group = lib.mkForce "buildkite-agents";
+          extraGroups = [ name ];
+        };
+      }) agents);
+    };
+  };
+}