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