longview service: don't write passwords to nix store

Adds services.longview.{apiKeyFile,mysqlPasswordFile} options as
alternatives to apiKey and mysqlPassword, which still work, but are
deprecated with a warning message.

Related to #24288.

nixos/modules/services/monitoring/longview.nix

···
 let
   cfg = config.services.longview;
 
-  pidFile = "/run/longview.pid";
-
-  apacheConf = optionalString (cfg.apacheStatusUrl != "") ''
-    location ${cfg.apacheStatusUrl}?auto
-  '';
-  mysqlConf = optionalString (cfg.mysqlUser != "") ''
-    username ${cfg.mysqlUser}
-    password ${cfg.mysqlPassword}
-  '';
-  nginxConf = optionalString (cfg.nginxStatusUrl != "") ''
-    location ${cfg.nginxStatusUrl}
-  '';
-
-in
+  runDir = "/run/longview";
+  configsDir = "${runDir}/longview.d";
 
-{
+in {
   options = {
 
     services.longview = {
···
 
       apiKey = mkOption {
         type = types.str;
+        default = "";
         example = "01234567-89AB-CDEF-0123456789ABCDEF";
         description = ''
           Longview API key. To get this, look in Longview settings which
           are found at https://manager.linode.com/longview/.
+
+          Warning: this secret is stored in the world-readable Nix store!
+          Use <option>apiKeyFile</option> instead.
+        '';
+      };
+
+      apiKeyFile = mkOption {
+        type = types.nullOr types.path;
+        default = null;
+        example = "/run/keys/longview-api-key";
+        description = ''
+          A file containing the Longview API key.
+          To get this, look in Longview settings which
+          are found at https://manager.linode.com/longview/.
+
+          <option>apiKeyFile</option> takes precedence over <option>apiKey</option>.
         '';
       };
 
···
 
       mysqlPassword = mkOption {
         type = types.str;
+        default = "";
         description = ''
-          The password corresponding to mysqlUser.  Warning: this is
-          stored in cleartext in the Nix store!
+          The password corresponding to <option>mysqlUser</option>.
+          Warning: this is stored in cleartext in the Nix store!
+          Use <option>mysqlPasswordFile</option> instead.
+        '';
+      };
+
+      mysqlPasswordFile = mkOption {
+        type = types.nullOr types.path;
+        default = null;
+        example = "/run/keys/dbpassword";
+        description = ''
+          A file containing the password corresponding to <option>mysqlUser</option>.
         '';
       };
+
     };
 
   };
···
         serviceConfig.Type = "forking";
         serviceConfig.ExecStop = "-${pkgs.coreutils}/bin/kill -TERM $MAINPID";
         serviceConfig.ExecReload = "-${pkgs.coreutils}/bin/kill -HUP $MAINPID";
-        serviceConfig.PIDFile = pidFile;
+        serviceConfig.PIDFile = "${runDir}/longview.pid";
         serviceConfig.ExecStart = "${pkgs.longview}/bin/longview";
+        preStart = ''
+          umask 077
+          mkdir -p ${configsDir}
+        '' + (optionalString (cfg.apiKeyFile != null) ''
+          cp --no-preserve=all "${cfg.apiKeyFile}" ${runDir}/longview.key
+        '') + (optionalString (cfg.apacheStatusUrl != "") ''
+          cat > ${configsDir}/Apache.conf <<EOF
+          location ${cfg.apacheStatusUrl}?auto
+          EOF
+        '') + (optionalString (cfg.mysqlUser != "" && cfg.mysqlPasswordFile != null) ''
+          cat > ${configsDir}/MySQL.conf <<EOF
+          username ${cfg.mysqlUser}
+          password `head -n1 "${cfg.mysqlPasswordFile}"`
+          EOF
+        '') + (optionalString (cfg.nginxStatusUrl != "") ''
+          cat > ${configsDir}/Nginx.conf <<EOF
+          location ${cfg.nginxStatusUrl}
+          EOF
+        '');
       };
 
-    environment.etc."linode/longview.key" = {
-      mode = "0400";
-      text = cfg.apiKey;
-    };
-    environment.etc."linode/longview.d/Apache.conf" = {
-      mode = "0400";
-      text = apacheConf;
-    };
-    environment.etc."linode/longview.d/MySQL.conf" = {
-      mode = "0400";
-      text = mysqlConf;
-    };
-    environment.etc."linode/longview.d/Nginx.conf" = {
-      mode = "0400";
-      text = nginxConf;
-    };
+    warnings = let warn = k: optional (cfg.${k} != "")
+                 "config.services.longview.${k} is insecure. Use ${k}File instead.";
+               in concatMap warn [ "apiKey" "mysqlPassword" ];
+
+    assertions = [
+      { assertion = cfg.apiKeyFile != null;
+        message = "Longview needs an API key configured";
+      }
+    ];
+
+    # Create API key file if not configured.
+    services.longview.apiKeyFile = mkIf (cfg.apiKey != "")
+      (mkDefault (toString (pkgs.writeTextFile {
+        name = "longview.key";
+        text = cfg.apiKey;
+      })));
+
+    # Create MySQL password file if not configured.
+    services.longview.mysqlPasswordFile = mkDefault (toString (pkgs.writeTextFile {
+      name = "mysql-password-file";
+      text = cfg.mysqlPassword;
+    }));
   };
 }

pkgs/servers/monitoring/longview/default.nix

···
     ./log-stdout.patch
   ];
 
+  # Read all configuration from /run/longview
   postPatch = ''
-    substituteInPlace Linode/Longview/Util.pm --replace /var/run/longview.pid /run/longview.pid
+    substituteInPlace Linode/Longview/Util.pm \
+        --replace /var/run/longview.pid /run/longview/longview.pid \
+        --replace /etc/linode /run/longview
+    substituteInPlace Linode/Longview.pl \
+        --replace /etc/linode /run/longview
   '';
 
   buildInputs = [ perl makeWrapper glibc ]