nixos/kubernetes: major module refactor

- All kubernetes components have been seperated into different files
- All TLS-enabled ports have been deprecated and disabled by default
- EasyCert option added to support automatic cluster PKI-bootstrap
- RBAC has been enforced for all cluster components by default
- NixOS kubernetes test cases make use of easyCerts to setup PKI

nixos/modules/services/cluster/kubernetes/scheduler.nix

@@ -0,0 +1,92 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  top = config.services.kubernetes;
+  cfg = top.scheduler;
+in
+{
+  ###### interface
+  options.services.kubernetes.scheduler = with lib.types; {
+
+    address = mkOption {
+      description = "Kubernetes scheduler listening address.";
+      default = "127.0.0.1";
+      type = str;
+    };
+
+    enable = mkEnableOption "Whether to enable Kubernetes scheduler.";
+
+    extraOpts = mkOption {
+      description = "Kubernetes scheduler extra command line options.";
+      default = "";
+      type = str;
+    };
+
+    featureGates = mkOption {
+      description = "List set of feature gates";
+      default = top.featureGates;
+      type = listOf str;
+    };
+
+    kubeconfig = top.lib.mkKubeConfigOptions "Kubernetes scheduler";
+
+    leaderElect = mkOption {
+      description = "Whether to start leader election before executing main loop.";
+      type = bool;
+      default = true;
+    };
+
+    port = mkOption {
+      description = "Kubernetes scheduler listening port.";
+      default = 10251;
+      type = int;
+    };
+
+    verbosity = mkOption {
+      description = ''
+        Optional glog verbosity level for logging statements. See
+        <link xlink:href="https://github.com/kubernetes/community/blob/master/contributors/devel/logging.md"/>
+      '';
+      default = null;
+      type = nullOr int;
+    };
+
+  };
+
+  ###### implementation
+  config = mkIf cfg.enable {
+    systemd.services.kube-scheduler = {
+      description = "Kubernetes Scheduler Service";
+      wantedBy = [ "kubernetes.target" ];
+      after = [ "kube-apiserver.service" ];
+      serviceConfig = {
+        Slice = "kubernetes.slice";
+        ExecStart = ''${top.package}/bin/kube-scheduler \
+          --address=${cfg.address} \
+          ${optionalString (cfg.featureGates != [])
+            "--feature-gates=${concatMapStringsSep "," (feature: "${feature}=true") cfg.featureGates}"} \
+          --kubeconfig=${top.lib.mkKubeConfig "kube-scheduler" cfg.kubeconfig} \
+          --leader-elect=${boolToString cfg.leaderElect} \
+          --port=${toString cfg.port} \
+          ${optionalString (cfg.verbosity != null) "--v=${toString cfg.verbosity}"} \
+          ${cfg.extraOpts}
+        '';
+        WorkingDirectory = top.dataDir;
+        User = "kubernetes";
+        Group = "kubernetes";
+      };
+    };
+
+    services.kubernetes.pki.certs = {
+      schedulerClient = top.lib.mkCert {
+        name = "kube-scheduler-client";
+        CN = "system:kube-scheduler";
+        action = "systemctl restart kube-scheduler.service";
+      };
+    };
+
+    services.kubernetes.scheduler.kubeconfig.server = mkDefault top.apiserverAddress;
+  };
+}