nixos/k3s: add initial k3s service

* nixos/k3s: simplify config expression

* nixos/k3s: add config assertions and trim unneeded bits

* nixos/k3s: add a test that k3s works; minor module improvements

This is a single-node test. Eventually we should also have a multi-node
test to verify the agent bit works, but that one's more involved.

* nixos/k3s: add option description

* nixos/k3s: add defaults for token/serveraddr

Now that the assertion enforces their presence, we dont' need to use the typesystem for it.

* nixos/k3s: remove unneeded sudo in test

* nixos/k3s: add to test list

1 files changed, 101 insertions, 0 deletions

diff --git a/nixos/modules/services/cluster/k3s/default.nix b/nixos/modules/services/cluster/k3s/default.nix
new file mode 100644
index 00000000000..ccdf54d128e
--- /dev/null
+++ b/nixos/modules/services/cluster/k3s/default.nix
@@ -0,0 +1,101 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+let
+  cfg = config.services.k3s;
+in
+{
+  # interface
+  options.services.k3s = {
+    enable = mkEnableOption "k3s";
+
+    package = mkOption {
+      type = types.package;
+      default = pkgs.k3s;
+      defaultText = "pkgs.k3s";
+      example = literalExample "pkgs.k3s";
+      description = "Package that should be used for k3s";
+    };
+
+    role = mkOption {
+      description = ''
+        Whether k3s should run as a server or agent.
+        Note that the server, by default, also runs as an agent.
+      '';
+      default = "server";
+      type = types.enum [ "server" "agent" ];
+    };
+
+    serverAddr = mkOption {
+      type = types.str;
+      description = "The k3s server to connect to. This option only makes sense for an agent.";
+      example = "https://10.0.0.10:6443";
+      default = "";
+    };
+
+    token = mkOption {
+      type = types.str;
+      description = "The k3s token to use when connecting to the server. This option only makes sense for an agent.";
+      default = "";
+    };
+
+    docker = mkOption {
+      type = types.bool;
+      default = false;
+      description = "Use docker to run containers rather than the built-in containerd.";
+    };
+
+    extraFlags = mkOption {
+      description = "Extra flags to pass to the k3s command.";
+      default = "";
+      example = "--no-deploy traefik --cluster-cidr 10.24.0.0/16";
+    };
+
+    disableAgent = mkOption {
+      type = types.bool;
+      default = false;
+      description = "Only run the server. This option only makes sense for a server.";
+    };
+  };
+
+  # implementation
+
+  config = mkIf cfg.enable {
+    assertions = [
+      {
+        assertion = cfg.role == "agent" -> cfg.serverAddr != "";
+        message = "serverAddr should be set if role is 'agent'";
+      }
+      {
+        assertion = cfg.role == "agent" -> cfg.token != "";
+        message = "token should be set if role is 'agent'";
+      }
+    ];
+
+    virtualisation.docker = mkIf cfg.docker {
+      enable = mkDefault true;
+    };
+
+    systemd.services.k3s = {
+      description = "k3s service";
+      after = mkIf cfg.docker [ "docker.service" ];
+      wantedBy = [ "multi-user.target" ];
+      serviceConfig = {
+        # Taken from https://github.com/rancher/k3s/blob/v1.17.4+k3s1/contrib/ansible/roles/k3s/node/templates/k3s.service.j2
+        Type = "notify";
+        KillMode = "process";
+        Delegate = "yes";
+        Restart = "always";
+        RestartSec = "5s";
+        ExecStart = concatStringsSep " \\\n " (
+          [
+            "${cfg.package}/bin/k3s ${cfg.role}"
+          ] ++ (optional cfg.docker "--docker")
+          ++ (optional cfg.disableAgent "--disable-agent")
+          ++ (optional (cfg.role == "agent") "--server ${cfg.serverAddr} --token ${cfg.token}")
+          ++ [ cfg.extraFlags ]
+        );
+      };
+    };
+  };
+}