Merge pull request #266702 from nh2/plausible-listen-address-no-distributed-erlang

plausible, nixos/plausible: Add `listenAddress` option

nixos/doc/manual/release-notes/rl-2311.section.md

@@ -323,6 +323,8 @@
 
 - Package `pash` was removed due to being archived upstream. Use `powershell` as an alternative.
 
+- The option `services.plausible.releaseCookiePath` has been removed: Plausible does not use any distributed Erlang features, and does not plan to (see [discussion](https://github.com/NixOS/nixpkgs/pull/130297#issuecomment-1805851333)), so NixOS now disables them, and the Erlang cookie becomes unnecessary. You may delete the file that `releaseCookiePath` was set to.
+
 - `security.sudo.extraRules` now includes `root`'s default rule, with ordering
   priority 400. This is functionally identical for users not specifying rule
   order, or relying on `mkBefore` and `mkAfter`, but may impact users calling

nixos/modules/services/web-apps/plausible.nix

@@ -11,13 +11,6 @@ in {
 
     package = mkPackageOptionMD pkgs "plausible" { };
 
-    releaseCookiePath = mkOption {
-      type = with types; either str path;
-      description = lib.mdDoc ''
-        The path to the file with release cookie. (used for remote connection to the running node).
-      '';
-    };
-
     adminUser = {
       name = mkOption {
         default = "admin";
@@ -92,6 +85,13 @@ in {
           framework docs](https://hexdocs.pm/phoenix/Mix.Tasks.Phx.Gen.Secret.html#content).
         '';
       };
+      listenAddress = mkOption {
+        default = "127.0.0.1";
+        type = types.str;
+        description = lib.mdDoc ''
+          The IP address on which the server is listening.
+        '';
+      };
       port = mkOption {
         default = 8000;
         type = types.port;
@@ -162,6 +162,10 @@ in {
     };
   };
 
+  imports = [
+    (mkRemovedOptionModule [ "services" "plausible" "releaseCookiePath" ] "Plausible uses no distributed Erlang features, so this option is no longer necessary and was removed")
+  ];
+
   config = mkIf cfg.enable {
     assertions = [
       { assertion = cfg.adminUser.activate -> cfg.database.postgres.setup;
@@ -180,8 +184,6 @@ in {
       enable = true;
     };
 
-    services.epmd.enable = true;
-
     environment.systemPackages = [ cfg.package ];
 
     systemd.services = mkMerge [
@@ -209,6 +211,32 @@ in {
             # Configuration options from
             # https://plausible.io/docs/self-hosting-configuration
             PORT = toString cfg.server.port;
+            LISTEN_IP = cfg.server.listenAddress;
+
+            # Note [plausible-needs-no-erlang-distributed-features]:
+            # Plausible does not use, and does not plan to use, any of
+            # Erlang's distributed features, see:
+            #     https://github.com/plausible/analytics/pull/1190#issuecomment-1018820934
+            # Thus, disable distribution for improved simplicity and security:
+            #
+            # When distribution is enabled,
+            # Elixir spwans the Erlang VM, which will listen by default on all
+            # interfaces for messages between Erlang nodes (capable of
+            # remote code execution); it can be protected by a cookie; see
+            # https://erlang.org/doc/reference_manual/distributed.html#security).
+            #
+            # It would be possible to restrict the interface to one of our choice
+            # (e.g. localhost or a VPN IP) similar to how we do it with `listenAddress`
+            # for the Plausible web server; if distribution is ever needed in the future,
+            # https://github.com/NixOS/nixpkgs/pull/130297 shows how to do it.
+            #
+            # But since Plausible does not use this feature in any way,
+            # we just disable it.
+            RELEASE_DISTRIBUTION = "none";
+            # Additional safeguard, in case `RELEASE_DISTRIBUTION=none` ever
+            # stops disabling the start of EPMD.
+            ERL_EPMD_ADDRESS = "127.0.0.1";
+
             DISABLE_REGISTRATION = if isBool cfg.server.disableRegistration then boolToString cfg.server.disableRegistration else cfg.server.disableRegistration;
 
             RELEASE_TMP = "/var/lib/plausible/tmp";
@@ -238,7 +266,10 @@ in {
           path = [ cfg.package ]
             ++ optional cfg.database.postgres.setup config.services.postgresql.package;
           script = ''
-            export RELEASE_COOKIE="$(< $CREDENTIALS_DIRECTORY/RELEASE_COOKIE )"
+            # Elixir does not start up if `RELEASE_COOKIE` is not set,
+            # even though we set `RELEASE_DISTRIBUTION=none` so the cookie should be unused.
+            # Thus, make a random one, which should then be ignored.
+            export RELEASE_COOKIE=$(tr -dc A-Za-z0-9 < /dev/urandom | head -c 20)
             export ADMIN_USER_PWD="$(< $CREDENTIALS_DIRECTORY/ADMIN_USER_PWD )"
             export SECRET_KEY_BASE="$(< $CREDENTIALS_DIRECTORY/SECRET_KEY_BASE )"
 
@@ -265,7 +296,6 @@ in {
             LoadCredential = [
               "ADMIN_USER_PWD:${cfg.adminUser.passwordFile}"
               "SECRET_KEY_BASE:${cfg.server.secretKeybaseFile}"
-              "RELEASE_COOKIE:${cfg.releaseCookiePath}"
             ] ++ lib.optionals (cfg.mail.smtp.passwordFile != null) [ "SMTP_USER_PWD:${cfg.mail.smtp.passwordFile}"];
           };
         };

nixos/tests/plausible.nix

@@ -8,9 +8,6 @@ import ./make-test-python.nix ({ pkgs, lib, ... }: {
     virtualisation.memorySize = 4096;
     services.plausible = {
       enable = true;
-      releaseCookiePath = "${pkgs.runCommand "cookie" { } ''
-        ${pkgs.openssl}/bin/openssl rand -base64 64 >"$out"
-      ''}";
       adminUser = {
         email = "admin@example.org";
         passwordFile = "${pkgs.writeText "pwd" "foobar"}";
@@ -28,6 +25,10 @@ import ./make-test-python.nix ({ pkgs, lib, ... }: {
     machine.wait_for_unit("plausible.service")
     machine.wait_for_open_port(8000)
 
+    # Ensure that the software does not make not make the machine
+    # listen on any public interfaces by default.
+    machine.fail("ss -tlpn 'src = 0.0.0.0 or src = [::]' | grep LISTEN")
+
     machine.succeed("curl -f localhost:8000 >&2")
 
     machine.succeed("curl -f localhost:8000/js/script.js >&2")