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, 53 insertions, 0 deletions

diff --git a/ops/modules/smtprelay.nix b/ops/modules/smtprelay.nix
new file mode 100644
index 0000000000..d8e03b5794
--- /dev/null
+++ b/ops/modules/smtprelay.nix
@@ -0,0 +1,53 @@
+# NixOS module for configuring the simple SMTP relay.
+{ depot, pkgs, config, lib, ... }:
+
+let
+  inherit (builtins) attrValues mapAttrs;
+  inherit (lib)
+    concatStringsSep
+    mkEnableOption
+    mkIf
+    mkOption
+    types
+;
+
+  cfg = config.services.depot.smtprelay;
+  description = "Simple SMTP relay";
+
+  # Configuration values that are always overridden. In particular,
+  # `config` is specified to always load $StateDirectory/secure.config
+  # (so that passwords can be loaded from there) and logging is pinned
+  # to stdout for journald compatibility.
+  overrideArgs = {
+    logfile = "";
+    config = "/var/lib/smtprelay/secure.config";
+  };
+
+  # Creates the command line argument string for the service.
+  prepareArgs = args:
+    concatStringsSep " "
+      (attrValues (mapAttrs (key: value: "-${key} '${toString value}'")
+                            (args // overrideArgs)));
+in {
+  options.services.depot.smtprelay = {
+    enable = mkEnableOption description;
+    args = mkOption {
+      type = types.attrsOf types.str;
+      description = "Key value pairs for command line arguments";
+    };
+  };
+
+  config = mkIf cfg.enable {
+    systemd.services.smtprelay = {
+      inherit description;
+      script = "${depot.third_party.smtprelay}/bin/smtprelay ${prepareArgs cfg.args}";
+      wantedBy = [ "multi-user.target" ];
+
+      serviceConfig = {
+        Restart = "always";
+        StateDirectory = "smtprelay";
+        DynamicUser = true;
+      };
+    };
+  };
+}