nixos/traefik: Adapt to traefik v2

This commit:

1. Updates the path of the traefik package, so that the out output is
   used.
2. Adapts the configuration settings and options to Traefik v2.
3. Formats the NixOS traefik service using nixfmt.

nixos/modules/services/web-servers/traefik.nix

@@ -4,56 +4,88 @@ with lib;
 
 let
   cfg = config.services.traefik;
-  configFile =
-    if cfg.configFile == null then
-      pkgs.runCommand "config.toml" {
-        buildInputs = [ pkgs.remarshal ];
-        preferLocalBuild = true;
-      } ''
-        remarshal -if json -of toml \
-          < ${pkgs.writeText "config.json" (builtins.toJSON cfg.configOptions)} \
-          > $out
-      ''
-    else cfg.configFile;
-
+  dynamicConfigFile = if cfg.dynamicConfigFile == null then
+    pkgs.runCommand "config.toml" {
+      buildInputs = [ pkgs.remarshal ];
+      preferLocalBuild = true;
+    } ''
+      remarshal -if json -of toml \
+        < ${
+          pkgs.writeText "dynamic_config.json"
+          (builtins.toJSON cfg.dynamicConfigOptions)
+        } \
+        > $out
+    ''
+  else
+    cfg.dynamicConfigFile;
+  staticConfigFile = if cfg.staticConfigFile == null then
+    pkgs.runCommand "config.toml" {
+      buildInputs = [ pkgs.yj ];
+      preferLocalBuild = true;
+    } ''
+      yj -jt -i \
+        < ${
+          pkgs.writeText "static_config.json" (builtins.toJSON
+            (recursiveUpdate cfg.staticConfigOptions {
+              providers.file.filename = "${dynamicConfigFile}";
+            }))
+        } \
+        > $out
+    ''
+  else
+    cfg.staticConfigFile;
 in {
   options.services.traefik = {
     enable = mkEnableOption "Traefik web server";
 
-    configFile = mkOption {
+    staticConfigFile = mkOption {
       default = null;
-      example = literalExample "/path/to/config.toml";
+      example = literalExample "/path/to/static_config.toml";
       type = types.nullOr types.path;
       description = ''
-        Path to verbatim traefik.toml to use.
-        (Using that option has precedence over <literal>configOptions</literal>)
+        Path to traefik's static configuration to use.
+        (Using that option has precedence over <literal>staticConfigOptions</literal> and <literal>dynamicConfigOptions</literal>)
       '';
     };
 
-    configOptions = mkOption {
+    staticConfigOptions = mkOption {
       description = ''
-        Config for Traefik.
+        Static configuration for Traefik.
       '';
       type = types.attrs;
-      default = {
-        defaultEntryPoints = ["http"];
-        entryPoints.http.address = ":80";
-      };
+      default = { entryPoints.http.address = ":80"; };
       example = {
-        defaultEntrypoints = [ "http" ];
-        web.address = ":8080";
+        entryPoints.web.address = ":8080";
         entryPoints.http.address = ":80";
 
-        file = {};
-        frontends = {
-          frontend1 = {
-            backend = "backend1";
-            routes.test_1.rule = "Host:localhost";
-          };
-        };
-        backends.backend1 = {
-          servers.server1.url = "http://localhost:8000";
+        api = { };
+      };
+    };
+
+    dynamicConfigFile = mkOption {
+      default = null;
+      example = literalExample "/path/to/dynamic_config.toml";
+      type = types.nullOr types.path;
+      description = ''
+        Path to traefik's dynamic configuration to use.
+        (Using that option has precedence over <literal>dynamicConfigOptions</literal>)
+      '';
+    };
+
+    dynamicConfigOptions = mkOption {
+      description = ''
+        Dynamic configuration for Traefik.
+      '';
+      type = types.attrs;
+      default = { };
+      example = {
+        http.routers.router1 = {
+          rule = "Host(`localhost`)";
+          service = "service1";
         };
+
+        http.services.service1.loadBalancer.servers =
+          [{ url = "http://localhost:8080"; }];
       };
     };
 
@@ -61,7 +93,7 @@ in {
       default = "/var/lib/traefik";
       type = types.path;
       description = ''
-      Location for any persistent data traefik creates, ie. acme
+        Location for any persistent data traefik creates, ie. acme
       '';
     };
 
@@ -84,16 +116,15 @@ in {
   };
 
   config = mkIf cfg.enable {
-    systemd.tmpfiles.rules = [
-      "d '${cfg.dataDir}' 0700 traefik traefik - -"
-    ];
+    systemd.tmpfiles.rules = [ "d '${cfg.dataDir}' 0700 traefik traefik - -" ];
 
     systemd.services.traefik = {
       description = "Traefik web server";
       after = [ "network-online.target" ];
       wantedBy = [ "multi-user.target" ];
       serviceConfig = {
-        ExecStart = ''${cfg.package.bin}/bin/traefik --configfile=${configFile}'';
+        ExecStart =
+          "${cfg.package}/bin/traefik --configfile=${staticConfigFile}";
         Type = "simple";
         User = "traefik";
         Group = cfg.group;
@@ -120,6 +151,6 @@ in {
       isSystemUser = true;
     };
 
-    users.groups.traefik = {};
+    users.groups.traefik = { };
   };
 }