Index: src/applications/harbormaster/step/RemoteCommandBuildStepImplementation.php
===================================================================
--- /dev/null
+++ src/applications/harbormaster/step/RemoteCommandBuildStepImplementation.php
@@ -0,0 +1,139 @@
+<?php
+
+final class RemoteCommandBuildStepImplementation
+  extends VariableBuildStepImplementation {
+
+  public function getName() {
+    return pht('Run Remote Command');
+  }
+
+  public function getGenericDescription() {
+    return pht('Run a command on another machine.');
+  }
+
+  public function getDescription() {
+    $settings = $this->getSettings();
+
+    return pht(
+      'Run \'%s\' on \'%s\'.',
+      $settings['command'],
+      $settings['sshhost']);
+  }
+
+  public function execute(
+    HarbormasterBuild $build,
+    HarbormasterBuildStep $build_step) {
+
+    $settings = $this->getSettings();
+
+    $future = null;
+    if (empty($settings['sshkey'])) {
+      $future = new ExecFuture(
+        'ssh -o "StrictHostKeyChecking no" -p %s %s %s',
+        $settings['sshport'],
+        $settings['sshuser'].'@'.$settings['sshhost'],
+        $this->mergeVariables($build, $settings['command']));
+    } else {
+      $future = new ExecFuture(
+        'ssh -o "StrictHostKeyChecking no" -p %s -i %s %s %s',
+        $settings['sshport'],
+        $settings['sshkey'],
+        $settings['sshuser'].'@'.$settings['sshhost'],
+        $this->mergeVariables($build, $settings['command']));
+    }
+
+    $log_stdout = $build->createLog($build_step, "remote", "stdout");
+    $log_stderr = $build->createLog($build_step, "remote", "stderr");
+
+    $start_stdout = $log_stdout->start();
+    $start_stderr = $log_stderr->start();
+
+    // Read the next amount of available output every second.
+    while (!$future->isReady()) {
+      list($stdout, $stderr) = $future->read();
+      $log_stdout->append($stdout);
+      $log_stderr->append($stderr);
+      $future->discardBuffers();
+
+      // Check to see if we have moved from a "Building" status.  This
+      // can occur if the user cancels the build, in which case we want
+      // to terminate whatever we're doing and return as quickly as possible.
+      if ($build->checkForCancellation()) {
+        $log_stdout->finalize($start_stdout);
+        $log_stderr->finalize($start_stderr);
+        $future->resolveKill();
+        return;
+      }
+
+      // Wait one second before querying for more data.
+      sleep(1);
+    }
+
+    // Get the return value so we can log that as well.
+    list($err) = $future->resolve();
+
+    $log_stdout->finalize($start_stdout);
+    $log_stderr->finalize($start_stderr);
+
+    if ($err) {
+      $build->setBuildStatus(HarbormasterBuild::STATUS_FAILED);
+    }
+  }
+
+  public function validateSettings() {
+    $settings = $this->getSettings();
+
+    if ($settings['command'] === null || !is_string($settings['command'])) {
+      return false;
+    }
+    if ($settings['sshhost'] === null || !is_string($settings['sshhost'])) {
+      return false;
+    }
+    if ($settings['sshuser'] === null || !is_string($settings['sshuser'])) {
+      return false;
+    }
+    if ($settings['sshkey'] === null || !is_string($settings['sshkey'])) {
+      return false;
+    }
+    if ($settings['sshport'] === null || !is_int($settings['sshport']) ||
+        $settings['sshport'] <= 0 || $settings['sshport'] >= 65536) {
+      return false;
+    }
+
+    $whitelist = PhabricatorEnv::getEnvConfig(
+      'harbormaster.temporary.hosts.whitelist');
+    if (!in_array($settings['sshhost'], $whitelist)) {
+      return false;
+    }
+
+    return true;
+  }
+
+  public function getSettingDefinitions() {
+    return array(
+      'command' => array(
+        'name' => 'Command',
+        'description' => 'The command to execute on the remote machine.',
+        'type' => BuildStepImplementation::SETTING_TYPE_STRING),
+      'sshhost' => array(
+        'name' => 'SSH Host',
+        'description' => 'The SSH host that the command will be run on.',
+        'type' => BuildStepImplementation::SETTING_TYPE_STRING),
+      'sshport' => array(
+        'name' => 'SSH Port',
+        'description' => 'The SSH port to connect to.',
+        'type' => BuildStepImplementation::SETTING_TYPE_INTEGER,
+        'default' => 22), // TODO: 'default' doesn't do anything yet..
+      'sshuser' => array(
+        'name' => 'SSH Username',
+        'description' => 'The SSH username to use.',
+        'type' => BuildStepImplementation::SETTING_TYPE_STRING),
+      'sshkey' => array(
+        'name' => 'SSH Identity File',
+        'description' =>
+          'The path to the SSH identity file (private key) '.
+          'on the local web server.',
+        'type' => BuildStepImplementation::SETTING_TYPE_STRING));
+  }
+
+}