nixos/github-runner: init at v2.277.1

nixos/modules/module-list.nix

@@ -285,6 +285,7 @@
   ./services/continuous-integration/hail.nix
   ./services/continuous-integration/hercules-ci-agent/default.nix
   ./services/continuous-integration/hydra/default.nix
+  ./services/continuous-integration/github-runner.nix
   ./services/continuous-integration/gitlab-runner.nix
   ./services/continuous-integration/gocd-agent/default.nix
   ./services/continuous-integration/gocd-server/default.nix

nixos/modules/services/continuous-integration/github-runner.nix

@@ -0,0 +1,299 @@
+{ config, pkgs, lib, ... }:
+with lib;
+let
+  cfg = config.services.github-runner;
+  svcName = "github-runner";
+  systemdDir = "${svcName}/${cfg.name}";
+  # %t: Runtime directory root (usually /run); see systemd.unit(5)
+  runtimeDir = "%t/${systemdDir}";
+  # %S: State directory root (usually /var/lib); see systemd.unit(5)
+  stateDir = "%S/${systemdDir}";
+  # %L: Log directory root (usually /var/log); see systemd.unit(5)
+  logsDir = "%L/${systemdDir}";
+in
+{
+  options.services.github-runner = {
+    enable = mkOption {
+      default = false;
+      example = true;
+      description = ''
+        Whether to enable GitHub Actions runner.
+
+        Note: GitHub recommends using self-hosted runners with private repositories only. Learn more here:
+        <link xlink:href="https://docs.github.com/en/actions/hosting-your-own-runners/about-self-hosted-runners"
+        >About self-hosted runners</link>.
+      '';
+      type = lib.types.bool;
+    };
+
+    url = mkOption {
+      type = types.str;
+      description = ''
+        Repository to add the runner to.
+
+        Changing this option triggers a new runner registration.
+      '';
+      example = "https://github.com/nixos/nixpkgs";
+    };
+
+    tokenFile = mkOption {
+      type = types.path;
+      description = ''
+        The full path to a file which contains the runner registration token.
+        The file should contain exactly one line with the token without any newline.
+        The token can be used to re-register a runner of the same name but is time-limited.
+
+        Changing this option or the file's content triggers a new runner registration.
+      '';
+      example = "/run/secrets/github-runner/nixos.token";
+    };
+
+    name = mkOption {
+      # Same pattern as for `networking.hostName`
+      type = types.strMatching "^$|^[[:alnum:]]([[:alnum:]_-]{0,61}[[:alnum:]])?$";
+      description = ''
+        Name of the runner to configure. Defaults to the hostname.
+
+        Changing this option triggers a new runner registration.
+      '';
+      example = "nixos";
+      default = config.networking.hostName;
+    };
+
+    runnerGroup = mkOption {
+      type = types.nullOr types.str;
+      description = ''
+        Name of the runner group to add this runner to (defaults to the default runner group).
+
+        Changing this option triggers a new runner registration.
+      '';
+      default = null;
+    };
+
+    extraLabels = mkOption {
+      type = types.listOf types.str;
+      description = ''
+        Extra labels in addition to the default (<literal>["self-hosted", "Linux", "X64"]</literal>).
+
+        Changing this option triggers a new runner registration.
+      '';
+      example = literalExample ''[ "nixos" ]'';
+      default = [ ];
+    };
+
+    replace = mkOption {
+      type = types.bool;
+      description = ''
+        Replace any existing runner with the same name.
+
+        Without this flag, registering a new runner with the same name fails.
+      '';
+      default = false;
+    };
+
+    extraPackages = mkOption {
+      type = types.listOf types.package;
+      description = ''
+        Extra packages to add to <literal>PATH</literal> of the service to make them available to workflows.
+      '';
+      default = [ ];
+    };
+  };
+
+  config = mkIf cfg.enable {
+    warnings = optionals (isStorePath cfg.tokenFile) [
+      ''
+        `services.github-runner.tokenFile` points to the Nix store and, therefore, is world-readable.
+        Consider using a path outside of the Nix store to keep the token private.
+      ''
+    ];
+
+    systemd.services.${svcName} = {
+      description = "GitHub Actions runner";
+
+      wantedBy = [ "multi-user.target" ];
+      wants = [ "network-online.target" ];
+      after = [ "network.target" "network-online.target" ];
+
+      environment = {
+        HOME = runtimeDir;
+        RUNNER_ROOT = runtimeDir;
+      };
+
+      path = (with pkgs; [
+        bash
+        coreutils
+        git
+        gnutar
+        gzip
+      ]) ++ [
+        config.nix.package
+      ] ++ cfg.extraPackages;
+
+      serviceConfig = rec {
+        ExecStart = "${pkgs.github-runner}/bin/runsvc.sh";
+
+        # Does the following, sequentially:
+        # - Copy the current and the previous `tokenFile` to the $RUNTIME_DIRECTORY
+        #   and make it accessible to the service user to allow for a content
+        #   comparison.
+        # - If the module configuration or the token has changed, clear the state directory.
+        # - Configure the runner.
+        # - Copy the configured `tokenFile` to the $STATE_DIRECTORY and make it
+        #   inaccessible to the service user.
+        # - Set up the directory structure by creating the necessary symlinks.
+        ExecStartPre =
+          let
+            # Wrapper script which expects the full path of the state, runtime and logs
+            # directory as arguments. Overrides the respective systemd variables to provide
+            # unambiguous directory names. This becomes relevant, for example, if the
+            # caller overrides any of the StateDirectory=, RuntimeDirectory= or LogDirectory=
+            # to contain more than one directory. This causes systemd to set the respective
+            # environment variables with the path of all of the given directories, separated
+            # by a colon.
+            writeScript = name: lines: pkgs.writeShellScript "${svcName}-${name}.sh" ''
+              set -euo pipefail
+
+              STATE_DIRECTORY="$1"
+              RUNTIME_DIRECTORY="$2"
+              LOGS_DIRECTORY="$3"
+
+              ${lines}
+            '';
+            currentConfigPath = "$STATE_DIRECTORY/.nixos-current-config.json";
+            runnerRegistrationConfig = getAttrs [ "name" "tokenFile" "url" "runnerGroup" "extraLabels" ] cfg;
+            newConfigPath = builtins.toFile "${svcName}-config.json" (builtins.toJSON runnerRegistrationConfig);
+            currentConfigTokenFilename = ".current-token";
+            newConfigTokenFilename = ".new-token";
+            runnerCredFiles = [
+              ".credentials"
+              ".credentials_rsaparams"
+              ".runner"
+            ];
+            ownConfigTokens = writeScript "own-config-tokens" ''
+              # Copy current and new token file to runtime dir and make it accessible to the service user
+              cp ${escapeShellArg cfg.tokenFile} "$RUNTIME_DIRECTORY/${newConfigTokenFilename}"
+              chmod 600 "$RUNTIME_DIRECTORY/${newConfigTokenFilename}"
+              chown "$USER" "$RUNTIME_DIRECTORY/${newConfigTokenFilename}"
+
+              if [[ -e "$STATE_DIRECTORY/${currentConfigTokenFilename}" ]]; then
+                cp "$STATE_DIRECTORY/${currentConfigTokenFilename}" "$RUNTIME_DIRECTORY/${currentConfigTokenFilename}"
+                chmod 600 "$RUNTIME_DIRECTORY/${currentConfigTokenFilename}"
+                chown "$USER" "$RUNTIME_DIRECTORY/${currentConfigTokenFilename}"
+              fi
+            '';
+            disownConfigTokens = writeScript "disown-config-tokens" ''
+              # Make the token inaccessible to the runner service user
+              chmod 600 "$STATE_DIRECTORY/${currentConfigTokenFilename}"
+              chown root:root "$STATE_DIRECTORY/${currentConfigTokenFilename}"
+            '';
+            unconfigureRunner = writeScript "unconfigure" ''
+              differs=
+              # Set `differs = 1` if current and new runner config differ or if `currentConfigPath` does not exist
+              ${pkgs.diffutils}/bin/diff -q '${newConfigPath}' "${currentConfigPath}" >/dev/null 2>&1 || differs=1
+              # Also trigger a registration if the token content changed
+              ${pkgs.diffutils}/bin/diff -q \
+                "$RUNTIME_DIRECTORY"/{${currentConfigTokenFilename},${newConfigTokenFilename}} \
+                >/dev/null 2>&1 || differs=1
+
+              if [[ -n "$differs" ]]; then
+                echo "Config has changed, removing old runner state."
+                echo "The old runner will still appear in the GitHub Actions UI." \
+                  "You have to remove it manually."
+                find "$STATE_DIRECTORY/" -mindepth 1 -delete
+              fi
+            '';
+            configureRunner = writeScript "configure" ''
+              empty=$(ls -A "$STATE_DIRECTORY")
+              if [[ -z "$empty" ]]; then
+                echo "Configuring GitHub Actions Runner"
+                token=$(< "$RUNTIME_DIRECTORY"/${newConfigTokenFilename})
+                RUNNER_ROOT="$STATE_DIRECTORY" ${pkgs.github-runner}/bin/config.sh \
+                  --unattended \
+                  --work "$RUNTIME_DIRECTORY" \
+                  --url ${escapeShellArg cfg.url} \
+                  --token "$token" \
+                  --labels ${escapeShellArg (concatStringsSep "," cfg.extraLabels)} \
+                  --name ${escapeShellArg cfg.name} \
+                  ${optionalString cfg.replace "--replace"} \
+                  ${optionalString (cfg.runnerGroup != null) "--runnergroup ${escapeShellArg cfg.runnerGroup}"}
+
+                # Move the automatically created _diag dir to the logs dir
+                mkdir -p  "$STATE_DIRECTORY/_diag"
+                cp    -r  "$STATE_DIRECTORY/_diag/." "$LOGS_DIRECTORY/"
+                rm    -rf "$STATE_DIRECTORY/_diag/"
+
+                # Cleanup token from config
+                rm -f "$RUNTIME_DIRECTORY"/${currentConfigTokenFilename}
+                mv    "$RUNTIME_DIRECTORY"/${newConfigTokenFilename} "$STATE_DIRECTORY/${currentConfigTokenFilename}"
+
+                # Symlink to new config
+                ln -s '${newConfigPath}' "${currentConfigPath}"
+              fi
+            '';
+            setupRuntimeDir = writeScript "setup-runtime-dirs" ''
+              # Link _diag dir
+              ln -s "$LOGS_DIRECTORY" "$RUNTIME_DIRECTORY/_diag"
+
+              # Link the runner credentials to the runtime dir
+              ln -s "$STATE_DIRECTORY"/{${lib.concatStringsSep "," runnerCredFiles}} "$RUNTIME_DIRECTORY/"
+            '';
+          in
+          map (x: "${x} ${escapeShellArgs [ stateDir runtimeDir logsDir ]}") [
+            "+${ownConfigTokens}" # runs as root
+            unconfigureRunner
+            configureRunner
+            "+${disownConfigTokens}" # runs as root
+            setupRuntimeDir
+          ];
+
+        # Contains _diag
+        LogsDirectory = [ systemdDir ];
+        # Default RUNNER_ROOT which contains ephemeral Runner data
+        RuntimeDirectory = [ systemdDir ];
+        # Home of persistent runner data, e.g., credentials
+        StateDirectory = [ systemdDir ];
+        StateDirectoryMode = "0700";
+        WorkingDirectory = runtimeDir;
+
+        # By default, use a dynamically allocated user
+        DynamicUser = true;
+
+        KillMode = "process";
+        KillSignal = "SIGTERM";
+
+        # Hardening (may overlap with DynamicUser=)
+        # The following options are only for optimizing:
+        # systemd-analyze security github-runner
+        AmbientCapabilities = "";
+        CapabilityBoundingSet = "";
+        # ProtectClock= adds DeviceAllow=char-rtc r
+        DeviceAllow = "";
+        LockPersonality = true;
+        NoNewPrivileges = true;
+        PrivateDevices = true;
+        PrivateMounts = true;
+        PrivateTmp = true;
+        PrivateUsers = true;
+        ProtectClock = true;
+        ProtectControlGroups = true;
+        ProtectHome = true;
+        ProtectHostname = true;
+        ProtectKernelLogs = true;
+        ProtectKernelModules = true;
+        ProtectKernelTunables = true;
+        ProtectSystem = "strict";
+        RemoveIPC = true;
+        RestrictNamespaces = true;
+        RestrictRealtime = true;
+        RestrictSUIDSGID = true;
+        UMask = "0066";
+
+        # Needs network access
+        PrivateNetwork = false;
+        # Cannot be true due to Node
+        MemoryDenyWriteExecute = false;
+      };
+    };
+  };
+}