Add flake

Chopped-down version of heywoodlh's.

flake.nix

@@ -0,0 +1,76 @@
+{
+  description = "heywoodlh kubernetes flake";
+
+  inputs = {
+    # Base
+    nixpkgs.url = "github:NixOS/nixpkgs";
+    flake-utils.url = "github:numtide/flake-utils";
+    nix-kube-generators.url = "github:farcaller/nix-kube-generators";
+    nixhelm.url = "github:farcaller/nixhelm";
+
+    # Charts from Git
+    nfs-helm = {
+      url = "github:kubernetes-sigs/nfs-subdir-external-provisioner";
+      flake = false; # DRY this
+    };
+    longhorn = {
+      url = "github:longhorn/longhorn/19e8fefd3ace7fb66c3f3521fc471b60a829b155"; # v1.5.1
+      flake = false;
+    };
+    app-template = {
+      # These branch comments suck but they're necessary until NixOS/nix#8226.
+      url = "github:bjw-s/helm-charts/8bfc33eb8a3dbb989e56e3b61d65a28c3def358e"; # v2.2.0
+      flake = false;
+    };
+  };
+
+  outputs = inputs @ {
+    self,
+    nixpkgs,
+    flake-utils,
+    nix-kube-generators,
+    nixhelm,
+    nfs-helm,
+    longhorn,
+  }:
+    flake-utils.lib.eachDefaultSystem (system: let
+      pkgs = import nixpkgs {
+        inherit system;
+      };
+      kubelib = nix-kube-generators.lib { inherit pkgs; };
+    in {
+      packages = {
+        longhorn = pkgs.stdenv.mkDerivation {
+          name = "longhorn";
+          phases = [ "installPhase" ];
+          installPhase = ''
+            cp ${longhorn}/deploy/longhorn.yaml $out
+          '';
+        };
+
+        nfs-kube = (kubelib.buildHelmChart {
+          name = "nfs-subdir";
+          chart = "${nfs-helm}/charts/nfs-subdir-external-provisioner";
+          namespace = "kube-system";
+          values = {
+            fullnameOverride = "nfs-subdir";
+            image.tag = "v4.0.2";
+            nfs = {
+              path = "/nfs/svc";
+              server = "losangeles.eureka.lan";
+            };
+            storageClass.name = "nfs-subdir";
+          };
+        });
+      };
+      devShell = pkgs.mkShell {
+        name = "kubernetes-shell";
+        buildInputs = with pkgs; [
+          k9s
+          kubectl
+          kubernetes-helm
+        ];
+      };
+      formatter = pkgs.alejandra;
+    });
+}