diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -701,6 +701,8 @@
     'DrydockBlueprintCoreCustomField' => 'applications/drydock/customfield/DrydockBlueprintCoreCustomField.php',
     'DrydockBlueprintCreateController' => 'applications/drydock/controller/DrydockBlueprintCreateController.php',
     'DrydockBlueprintCustomField' => 'applications/drydock/customfield/DrydockBlueprintCustomField.php',
+    'DrydockBlueprintCustomFieldBlueprints' => 'applications/drydock/customfield/DrydockBlueprintCustomFieldBlueprints.php',
+    'DrydockBlueprintDatasource' => 'applications/drydock/typeahead/DrydockBlueprintDatasource.php',
     'DrydockBlueprintEditController' => 'applications/drydock/controller/DrydockBlueprintEditController.php',
     'DrydockBlueprintEditor' => 'applications/drydock/editor/DrydockBlueprintEditor.php',
     'DrydockBlueprintImplementation' => 'applications/drydock/blueprint/DrydockBlueprintImplementation.php',
@@ -881,6 +883,7 @@
     'HarbormasterDAO' => 'applications/harbormaster/storage/HarbormasterDAO.php',
     'HarbormasterHTTPRequestBuildStepImplementation' => 'applications/harbormaster/step/HarbormasterHTTPRequestBuildStepImplementation.php',
     'HarbormasterLeaseHostBuildStepImplementation' => 'applications/harbormaster/step/HarbormasterLeaseHostBuildStepImplementation.php',
+    'HarbormasterLeaseWorkingCopyBuildStepImplementation' => 'applications/harbormaster/step/HarbormasterLeaseWorkingCopyBuildStepImplementation.php',
     'HarbormasterManagePlansCapability' => 'applications/harbormaster/capability/HarbormasterManagePlansCapability.php',
     'HarbormasterManagementBuildWorkflow' => 'applications/harbormaster/management/HarbormasterManagementBuildWorkflow.php',
     'HarbormasterManagementUpdateWorkflow' => 'applications/harbormaster/management/HarbormasterManagementUpdateWorkflow.php',
@@ -3982,6 +3985,8 @@
     ),
     'DrydockBlueprintCreateController' => 'DrydockBlueprintController',
     'DrydockBlueprintCustomField' => 'PhabricatorCustomField',
+    'DrydockBlueprintCustomFieldBlueprints' => 'PhabricatorStandardCustomFieldPHIDs',
+    'DrydockBlueprintDatasource' => 'PhabricatorTypeaheadDatasource',
     'DrydockBlueprintEditController' => 'DrydockBlueprintController',
     'DrydockBlueprintEditor' => 'PhabricatorApplicationTransactionEditor',
     'DrydockBlueprintListController' => 'DrydockBlueprintController',
@@ -4213,6 +4218,7 @@
     'HarbormasterDAO' => 'PhabricatorLiskDAO',
     'HarbormasterHTTPRequestBuildStepImplementation' => 'HarbormasterBuildStepImplementation',
     'HarbormasterLeaseHostBuildStepImplementation' => 'HarbormasterBuildStepImplementation',
+    'HarbormasterLeaseWorkingCopyBuildStepImplementation' => 'HarbormasterBuildStepImplementation',
     'HarbormasterManagePlansCapability' => 'PhabricatorPolicyCapability',
     'HarbormasterManagementBuildWorkflow' => 'HarbormasterManagementWorkflow',
     'HarbormasterManagementUpdateWorkflow' => 'HarbormasterManagementWorkflow',
diff --git a/src/applications/drydock/blueprint/DrydockBlueprintImplementation.php b/src/applications/drydock/blueprint/DrydockBlueprintImplementation.php
--- a/src/applications/drydock/blueprint/DrydockBlueprintImplementation.php
+++ b/src/applications/drydock/blueprint/DrydockBlueprintImplementation.php
@@ -10,6 +10,7 @@
   private $activeResource;
   private $activeLease;
   private $instance;
+  private $scopes = array();
 
   abstract public function getType();
   abstract public function getInterface(
@@ -606,10 +607,11 @@
     DrydockResource $resource = null,
     DrydockLease $lease = null) {
 
-    if (($this->activeResource !== null) ||
-        ($this->activeLease !== null)) {
-      throw new Exception(pht('There is already an active resource or lease!'));
-    }
+    $scope = array(
+      'resource' => $resource,
+      'lease' => $lease,
+    );
+    array_push($this->scopes, $scope);
 
     $this->activeResource = $resource;
     $this->activeLease = $lease;
@@ -618,8 +620,20 @@
   }
 
   public function popActiveScope() {
-    $this->activeResource = null;
-    $this->activeLease = null;
+    if (count($this->scopes) === 0) {
+      throw new Exception('Unable to pop active scope; no scopes active');
+    }
+
+    array_pop($this->scopes);
+
+    if (count($this->scopes) === 0) {
+      $this->activeResource = null;
+      $this->activeLease = null;
+    } else {
+      $current = last($this->scopes);
+      $this->activeResource = $current['resource'];
+      $this->activeLease = $current['lease'];
+    }
   }
 
 }
diff --git a/src/applications/drydock/blueprint/DrydockWorkingCopyBlueprintImplementation.php b/src/applications/drydock/blueprint/DrydockWorkingCopyBlueprintImplementation.php
--- a/src/applications/drydock/blueprint/DrydockWorkingCopyBlueprintImplementation.php
+++ b/src/applications/drydock/blueprint/DrydockWorkingCopyBlueprintImplementation.php
@@ -3,6 +3,8 @@
 final class DrydockWorkingCopyBlueprintImplementation
   extends DrydockBlueprintImplementation {
 
+  private $cachedHostBlueprint = null;
+
   public function isEnabled() {
     return true;
   }
@@ -15,14 +17,180 @@
     return pht('Allows Drydock to check out working copies of repositories.');
   }
 
+  private function resolveRelatedObjectsForLease(DrydockLease $lease) {
+    if ($lease->getAttribute('resolved.target') !== null) {
+      return;
+    }
+
+    $url = $lease->getAttribute('url');
+    $buildable_phid = $lease->getAttribute('buildablePHID');
+
+    if ($url) {
+      $lease->setAttribute('resolved.target', 'url');
+      $lease->setAttribute('resolved.repositoryURL', $url);
+      $lease->save();
+
+      $this->log(pht(
+        'Resolved working copy target as "url"'));
+      $this->log(pht(
+        'Resolved working copy repository URL as "%s"',
+        $lease->getAttribute('resolved.repositoryURL')));
+    } else if ($buildable_phid) {
+      $buildable = id(new HarbormasterBuildableQuery())
+        ->setViewer(PhabricatorUser::getOmnipotentUser())
+        ->withPHIDs(array($buildable_phid))
+        ->needContainerObjects(true)
+        ->executeOne();
+      if ($buildable === null) {
+        throw new Exception(pht(
+          'No buildable found with PHID %s',
+          $buildable_phid));
+      }
+      $buildable_object = $buildable->getBuildableObject();
+      $container_object = $buildable->getContainerObject();
+
+      if ($buildable_object instanceof PhabricatorRepositoryCommit &&
+          $container_object instanceof PhabricatorRepository) {
+        $lease->setAttribute('resolved.target', 'commit');
+        $lease->setAttribute(
+          'resolved.commitIdentifier',
+          $buildable_object->getCommitIdentifier());
+        $lease->setAttribute(
+          'resolved.repositoryPHID',
+          $container_object->getPHID());
+        $lease->save();
+
+        $this->log(pht(
+          'Resolved working copy target as "commit"'));
+        $this->log(pht(
+          'Resolved working copy commit identifier as "%s"',
+          $lease->getAttribute('resolved.commitIdentifier')));
+        $this->log(pht(
+          'Resolved working copy repository PHID as "%s"',
+          $lease->getAttribute('resolved.repositoryPHID')));
+      } else if ($buildable_object instanceof DifferentialDiff &&
+                 $container_object instanceof DifferentialRevision) {
+        $lease->setAttribute('resolved.target', 'diff');
+        $lease->setAttribute(
+          'resolved.diffID',
+          $buildable_object->getID());
+        $lease->setAttribute(
+          'resolved.revisionID',
+          $container_object->getID());
+        $lease->setAttribute(
+          'resolved.repositoryPHID',
+          $container_object->getRepository()->getPHID());
+        $lease->setAttribute(
+          'resolved.baseRevision',
+          $buildable_object->getSourceControlBaseRevision());
+        $lease->save();
+
+        $this->log(pht(
+          'Resolved working copy target as "diff"'));
+        $this->log(pht(
+          'Resolved working copy diff ID as "%d"',
+          $lease->getAttribute('resolved.diffID')));
+        $this->log(pht(
+          'Resolved working copy revision ID as "%d"',
+          $lease->getAttribute('resolved.revisionID')));
+        $this->log(pht(
+          'Resolved working copy repository PHID as "%s"',
+          $lease->getAttribute('resolved.repositoryPHID')));
+        $this->log(pht(
+          'Resolved working copy base revision as "%s"',
+          $lease->getAttribute('resolved.baseRevision')));
+      }
+    }
+  }
+
+  private function getHostBlueprintPHID() {
+    return head(phutil_json_decode($this->getDetail('host-blueprint')));
+  }
+
+  private function getHostBlueprint() {
+    if ($this->cachedHostBlueprint !== null) {
+      return $this->cachedHostBlueprint;
+    }
+
+    $host_blueprint = id(new DrydockBlueprintQuery())
+      ->setViewer(PhabricatorUser::getOmnipotentUser())
+      ->withPHIDs(array($this->getHostBlueprintPHID()))
+      ->executeOne();
+    if (!$host_blueprint) {
+      throw new Exception(pht(
+        'This blueprint does not have a valid host blueprint.'));
+    }
+
+    $this->cachedHostBlueprint = $host_blueprint;
+    return $host_blueprint;
+  }
+
+  public function canAllocateResourceForLease(DrydockLease $lease) {
+    $host_blueprint = $this->getHostBlueprint();
+
+    $host_platform = $host_blueprint->getDetail('platform');
+    if ($host_platform === null) {
+      $host_platform = $this->getDetail('host-platform');
+    }
+
+    $lease_platform = $lease->getAttribute('platform');
+
+    return $host_platform === $lease_platform;
+  }
+
   protected function canAllocateLease(
     DrydockResource $resource,
     DrydockLease $lease) {
 
-    $resource_repo = $resource->getAttribute('repositoryID');
-    $lease_repo = $lease->getAttribute('repositoryID');
+    $lease_platform = $lease->getAttribute('platform');
+    $resource_platform = $resource->getAttribute('platform');
+
+    $platform_match = $lease_platform === $resource_platform;
+
+    $custom_match = DrydockCustomAttributes::hasRequirements(
+      $lease->getAttributes(),
+      $this->getDetail('attributes'));
+
+    $host_lease_id = $lease->getAttribute('hostLeaseID');
+    if ($host_lease_id !== null) {
+      $host_lease = id(new DrydockLeaseQuery())
+        ->setViewer(PhabricatorUser::getOmnipotentUser())
+        ->withIDs(array($host_lease_id))
+        ->executeOne();
+      if ($host_lease === null) {
+        throw new Exception(pht(
+          'No lease found with ID %d',
+          $host_lease_id));
+      }
+      if ($host_lease->getResource()->getBlueprint()->getPHID()
+        !== $this->getHostBlueprintPHID()) {
+        $this->log(pht(
+          'This blueprint can not allocate a resource on the required host.'));
+        return false;
+      }
+    }
+
+    $resource_repo = $resource->getAttribute('repositoryPHID');
+    $resource_url = $resource->getAttribute('repositoryURL');
+
+    $this->resolveRelatedObjectsForLease($lease);
 
-    return ($resource_repo && $lease_repo && ($resource_repo == $lease_repo));
+    $lease_repo = $lease->getAttribute('resolved.repositoryPHID');
+    $lease_url = $lease->getAttribute('resolved.repositoryURL');
+
+    $can_allocate = $platform_match && $custom_match &&
+      (($resource_repo && $lease_repo && ($resource_repo == $lease_repo)) ||
+      ($resource_url && $lease_url && ($resource_url == $lease_url)));
+
+    if ($can_allocate) {
+      $this->log(pht(
+        'This blueprint can allocate a resource for the specified lease.'));
+    } else {
+      $this->log(pht(
+        'This blueprint can not allocate a resource for the specified lease.'));
+    }
+
+    return $can_allocate;
   }
 
   protected function shouldAllocateLease(
@@ -30,77 +198,449 @@
     DrydockResource $resource,
     DrydockLease $lease) {
 
-    return $context->getCurrentResourceLeaseCount() === 0;
+    return true;
   }
 
   protected function executeInitializePendingResource(
     DrydockResource $resource,
-    DrydockLease $lease) {}
+    DrydockLease $lease) {
+
+    $this->resolveRelatedObjectsForLease($lease);
+
+    $target = $lease->getAttribute('resolved.target');
+    if (!$target) {
+      throw new Exception(
+        'Unable to resolve working copy target for lease.');
+    }
+
+    $repository_phid = $lease->getAttribute('resolved.repositoryPHID');
+    $repository_url = $lease->getAttribute('resolved.repositoryURL');
+
+    // We must set the platform so that other allocators will lease
+    // against it successfully.
+    $resource
+      ->setAttribute('platform', $lease->getAttribute('platform'))
+      ->setAttribute('repositoryPHID', $repository_phid)
+      ->setAttribute('repositoryURL', $repository_url)
+      ->save();
+  }
 
   protected function executeAllocateResource(
     DrydockResource $resource,
     DrydockLease $lease) {
 
-    $repository_id = $lease->getAttribute('repositoryID');
-    if (!$repository_id) {
-      throw new Exception(
-        pht(
-          "Lease is missing required '%s' attribute.",
-          'repositoryID'));
+    $repository_phid = $lease->getAttribute('resolved.repositoryPHID');
+    $repository_url = $lease->getAttribute('resolved.repositoryURL');
+
+    if ($repository_url) {
+      $resource
+        ->setName('Working Copy ('.$repository_url.')')
+        ->setStatus(DrydockResourceStatus::STATUS_PENDING)
+        ->setAttribute('repositoryURL', $repository_url)
+        ->setAttribute('platform', $lease->getAttribute('platform'))
+        ->save();
+    } else if ($repository_phid) {
+      $repository = id(new PhabricatorRepositoryQuery())
+        ->setViewer(PhabricatorUser::getOmnipotentUser())
+        ->withPHIDs(array($repository_phid))
+        ->executeOne();
+
+      if (!$repository) {
+        throw new Exception(
+          "Repository with PHID '{$repository_phid}' does not exist!");
+      }
+
+      switch ($repository->getVersionControlSystem()) {
+        case PhabricatorRepositoryType::REPOSITORY_TYPE_GIT:
+          break;
+        default:
+          throw new Exception(pht('Unsupported VCS!'));
+      }
+
+      $resource
+        ->setName('Working Copy ('.$repository->getCallsign().')')
+        ->setStatus(DrydockResourceStatus::STATUS_PENDING)
+        ->setAttribute('repositoryPHID', $repository->getPHID())
+        ->setAttribute('platform', $lease->getAttribute('platform'))
+        ->save();
     }
 
-    $repository = id(new PhabricatorRepositoryQuery())
-      ->setViewer(PhabricatorUser::getOmnipotentUser())
-      ->withIDs(array($repository_id))
-      ->executeOne();
-
-    if (!$repository) {
-      throw new Exception(
-        pht(
-          "Repository '%s' does not exist!",
-          $repository_id));
+    // When allocating the resource, we always need to get a new lease
+    // that is owned by the resource.  If the lease has specified an
+    // existing lease, we can a new lease against the same resource as
+    // that lease.
+
+    $host_lease = null;
+    $host_lease_id = $lease->getAttribute('hostLeaseID');
+    $resource_id = null;
+    if ($host_lease_id !== null) {
+      $host_lease = id(new DrydockLeaseQuery())
+        ->setViewer(PhabricatorUser::getOmnipotentUser())
+        ->withIDs(array($host_lease_id))
+        ->executeOne();
+      if ($host_lease === null) {
+        throw new Exception(pht(
+          'No lease found with ID %d',
+          $host_lease_id));
+      }
+      $resource_id = $host_lease->getResource()->getID();
     }
 
-    switch ($repository->getVersionControlSystem()) {
-      case PhabricatorRepositoryType::REPOSITORY_TYPE_GIT:
-        break;
-      default:
-        throw new Exception(pht('Unsupported VCS!'));
+    if ($resource_id) {
+      $this->log(pht(
+        'Limiting lease acquisition to resource ID %d.',
+        $resource_id));
     }
 
-    // TODO: Policy stuff here too.
-    $host_lease = id(new DrydockLease())
+    $this->log('Acquiring new host lease for working copy...');
+
+    $resource_lease = id(new DrydockLease())
       ->setResourceType('host')
+      ->setAttributes(
+        array(
+          'resourceID' => $resource_id,
+          'platform' => $lease->getAttribute('platform'),
+        ))
       ->waitUntilActive();
 
-    $path = $host_lease->getAttribute('path').$repository->getCallsign();
+    $this->log(pht(
+      'Lease %d acquired for working copy resource.',
+      $resource_lease->getID()));
 
-    $this->log(
-      pht('Cloning %s into %s....', $repository->getCallsign(), $path));
+    if ($lease->getAttribute('platform') === 'windows') {
+      $cmd = $resource_lease->getInterface(
+        'command-'.PhutilCommandString::MODE_WINDOWSCMD);
+    } else {
+      $cmd = $resource_lease->getInterface(
+        'command-'.PhutilCommandString::MODE_BASH);
+    }
 
-    $cmd = $host_lease->getInterface('command');
-    $cmd->execx(
-      'git clone --origin origin %P %s',
-      $repository->getRemoteURIEnvelope(),
-      $path);
+    if ($repository_phid) {
+      $this->log(pht(
+        'Cloning repository at "%s" to "%s"...',
+        $repository->getPublicCloneURI(),
+        $resource_lease->getAttribute('path')));
+
+      $cmd->execx(
+        'git clone --bare %s .',
+        $repository->getPublicCloneURI());
+    } else {
+      $this->log(pht(
+        'Cloning repository at "%s" to "%s"...',
+        $resource->getAttribute('repositoryURL'),
+        $resource_lease->getAttribute('path')));
+
+      $cmd->execx(
+        'git clone --bare %s .',
+        $resource->getAttribute('repositoryURL'));
+    }
 
-    $this->log(pht('Complete.'));
+    $this->log('Cloned repository cache.');
 
     $resource
-      ->setName('Working Copy ('.$repository->getCallsign().')')
       ->setStatus(DrydockResourceStatus::STATUS_OPEN)
-      ->setAttribute('lease.host', $host_lease->getID())
-      ->setAttribute('path', $path)
-      ->setAttribute('repositoryID', $repository->getID())
+      ->setAttribute('host.lease', $resource_lease->getID())
+      ->setAttribute('host.resource', $resource_lease->getResource()->getID())
+      ->setAttribute('path', $resource_lease->getAttribute('path'))
+      ->setAttribute('platform', $resource_lease->getAttribute('platform'))
       ->save();
-
     return $resource;
   }
 
   protected function executeAcquireLease(
     DrydockResource $resource,
     DrydockLease $lease) {
-    return;
+
+    $this->log(pht(
+      'Starting acquisition of lease from resource %d',
+      $resource->getID()));
+
+    while ($resource->getStatus() == DrydockResourceStatus::STATUS_PENDING) {
+      $this->log(pht(
+        'Resource %d is still pending, waiting until it is in an open status',
+        $resource->getID()));
+
+      // This resource is still being set up by another allocator, wait until
+      // it is set to open.
+      sleep(5);
+      $resource->reload();
+    }
+
+    $resource_lease = id(new DrydockLeaseQuery())
+      ->setViewer(PhabricatorUser::getOmnipotentUser())
+      ->withIDs(array($resource->getAttribute('host.lease')))
+      ->executeOne();
+    if ($resource_lease === null) {
+      throw new Exception(pht(
+        'No resource found with ID %d',
+        $resource->getAttribute('host.lease')));
+    }
+
+    // We must lock the resource while we perform the cache update,
+    // because otherwise we'll end up running multiple read-write
+    // VCS operations in the same directory at the same time.
+    $lock = PhabricatorGlobalLock::newLock(
+      'drydock-working-copy-cache-update-'.$resource_lease->getID());
+    $lock->lock(1000000);
+    try {
+      if ($lease->getAttribute('platform') === 'windows') {
+        $cmd = $resource_lease->getInterface(
+          'command-'.PhutilCommandString::MODE_WINDOWSCMD);
+      } else {
+        $cmd = $resource_lease->getInterface(
+          'command-'.PhutilCommandString::MODE_BASH);
+      }
+
+      $this->log(pht(
+        'Fetching latest commits for repository at "%s"',
+        $resource->getAttribute('path')));
+      $cmd->exec('git fetch origin +refs/heads/*:refs/heads/*');
+      $this->log(pht('Fetched latest commits.'));
+
+      $lock->unlock();
+    } catch (Exception $ex) {
+      $lock->unlock();
+      throw $ex;
+    }
+
+    $host_lease = null;
+    if ($lease->getAttribute('cacheOnly')) {
+      // This is a cache-only lease; we just pass through the resource's
+      // attributes so we don't make an unnecessary copy.  This means the
+      // acquirer of the lease intends to clone from the resource's cache
+      // directly.
+      $this->log(pht(
+        'Cache-only lease requested, passing through resource lease directly'));
+      $lease
+        ->setAttribute('cacheOnly', true)
+        ->setAttribute('host.lease', $resource->getAttribute('host.lease'));
+      $host_lease = $resource_lease;
+    } else {
+      $host_lease_id = $lease->getAttribute('hostLeaseID');
+      if ($host_lease_id !== null) {
+        $host_lease = id(new DrydockLeaseQuery())
+          ->setViewer(PhabricatorUser::getOmnipotentUser())
+          ->withIDs(array($host_lease_id))
+          ->executeOne();
+        if ($host_lease === null) {
+          throw new Exception(pht(
+            'No lease found with ID %d',
+            $host_lease_id));
+        }
+        $this->log(pht(
+          'Using existing host lease %d for working copy resource.',
+          $host_lease_id));
+      } else {
+        $this->log('Acquiring new host lease for working copy...');
+        $host_lease = id(new DrydockLease())
+          ->setResourceType('host')
+          ->setAttributes(
+            array(
+              'resourceID' => $resource->getAttribute('host.resource'),
+              'platform' => $lease->getAttribute('platform'),
+            ))
+          ->waitUntilActive();
+        $host_lease_id = $host_lease->getID();
+        $this->log(pht(
+          'Lease %d acquired for working copy resource.',
+          $host_lease_id));
+      }
+
+      $lease->setAttribute('host.lease', $host_lease_id);
+
+      if ($lease->getAttribute('platform') === 'windows') {
+        $cmd = $lease->getInterface(
+          'command-'.PhutilCommandString::MODE_WINDOWSCMD);
+      } else {
+        $cmd = $lease->getInterface(
+          'command-'.PhutilCommandString::MODE_BASH);
+      }
+
+      $this->log(pht(
+        'Cloning from cache path "%s" to lease path "%s"',
+        $resource->getAttribute('path'),
+        $host_lease->getAttribute('path')));
+      $cmd->execx(
+        'git clone %s .',
+        $resource->getAttribute('path'));
+      $this->log(pht('Cloned from cache'));
+
+      if ($lease->getAttribute('resolved.target') === 'commit') {
+        $this->log(pht(
+          'Checking out target commit "%s"',
+          $lease->getAttribute('resolved.commitIdentifier')));
+        $cmd->execx(
+          'git checkout -f %s',
+          $lease->getAttribute('resolved.commitIdentifier'));
+        $this->log(pht('Checked out commit'));
+      } else if ($lease->getAttribute('resolved.target') === 'url') {
+        // Leave as default; we use the working copy for cloning only.
+      } else {
+        throw new Exception(pht(
+          'Target type %s not yet supported.',
+          $lease->getAttribute('resolved.target')));
+      }
+
+      $this->initializeSubmodules(
+        $host_lease,
+        $host_lease->getAttribute('path'));
+    }
+  }
+
+  private function initializeSubmodules(
+    DrydockLease $working_directory_lease,
+    $working_directory_path = null) {
+
+    if ($working_directory_lease->getAttribute('platform') === 'windows') {
+      $working_directory_cmd = $working_directory_lease->getInterface(
+        'command-'.PhutilCommandString::MODE_WINDOWSCMD);
+    } else {
+      $working_directory_cmd = $working_directory_lease->getInterface(
+        'command-'.PhutilCommandString::MODE_BASH);
+    }
+
+    $working_directory_cmd->setWorkingDirectory($working_directory_path);
+
+    $this->log(pht(
+      'Initializing submodules in %s',
+      $working_directory_path));
+    $working_directory_cmd->execx('git submodule init');
+    $this->log(pht(
+      'Initialized submodules in %s',
+      $working_directory_path));
+
+    $this->log(pht(
+      'Discovering initialized submodules in %s',
+      $working_directory_path));
+    list($stdout, $stderr) =
+      $working_directory_cmd->execx('git config --local --list');
+    $matches = null;
+    preg_match_all(
+      '/submodule\.(?<name>.*)\.url=(?<url>.*)/',
+      $stdout,
+      $matches);
+    $this->log(pht(
+      'Standard output is %s',
+      $stdout));
+    $this->log(pht(
+      'Submodule array is %s',
+      print_r($matches, true)));
+    $submodules = array();
+    for ($i = 0; $i < count($matches['name']); $i++) {
+      $name = $matches['name'][$i];
+      $url = $matches['url'][$i];
+
+      $submodules[$name] = $url;
+
+      $this->log(pht(
+        'Discovered submodule %s registered with URL %s',
+        $name,
+        $url));
+    }
+
+    foreach ($submodules as $name => $url) {
+      $this->log(pht(
+        'Caching submodule at URL %s by leasing working copy',
+        $url));
+
+      $submodule_lease = id(new DrydockLease())
+        ->setResourceType('working-copy')
+        ->setAttributes(
+          array(
+            'platform' => $working_directory_lease->getAttribute('platform'),
+            'hostLeaseID' =>
+              $working_directory_lease->getAttribute('hostLeaseID'),
+            'url' => $url,
+            'cacheOnly' => true,
+          ))
+        ->queueForActivation();
+
+      $this->log(pht(
+        'Starting submodule lease %d',
+        $submodule_lease->getID()));
+
+      $submodule_lease->waitUntilActive();
+
+      $this->log(pht(
+        'Acquired submodule lease %d',
+        $submodule_lease->getID()));
+
+      // Load the host leases for both the submodule working directory.
+      $submodule_working_directory_lease_id =
+        $submodule_lease->getAttribute('host.lease');
+
+      $this->log(pht(
+        'Submodule working directory host lease ID is %d',
+        $submodule_working_directory_lease_id));
+
+      $submodule_leases = id(new DrydockLeaseQuery())
+        ->setViewer(PhabricatorUser::getOmnipotentUser())
+        ->withIDs(array(
+          $submodule_working_directory_lease_id,
+          ))
+        ->execute();
+      $submodule_leases = mpull($submodule_leases, null, 'getID');
+      $submodule_working_directory_lease =
+        idx($submodule_leases, $submodule_working_directory_lease_id);
+
+      $submodule_working_directory =
+        $submodule_working_directory_lease->getAttribute('path');
+
+      $this->log(pht(
+        'Updating local submodule URL to point to %s',
+        $submodule_working_directory));
+
+      $working_directory_cmd->execx(
+        'git config --local submodule.%s.url %s',
+        $name,
+        $submodule_working_directory);
+
+      $this->log(pht(
+        'Updating submodule %s',
+        $name));
+
+      $working_directory_cmd->execx('git submodule update %s', $name);
+
+      $this->log(pht(
+        'Loading leases for submodule %s',
+        $name));
+
+      $this->log(pht(
+        'Recursively initializing submodules from cache for %s',
+        $name));
+
+      $this->initializeSubmodules(
+        $submodule_working_directory_lease,
+        $working_directory_path.'/'.$name);
+
+      $this->log(pht(
+        'Recursive submodule initialization complete for %s',
+        $name));
+
+      $submodule_lease_id = $submodule_lease->getID();
+      $this->log(pht(
+        'Releasing lease for %d',
+        $submodule_lease_id));
+
+      $submodule_lease->release();
+
+      $this->log(pht(
+        'Released lease for %d',
+        $submodule_lease_id));
+
+      $this->log(pht(
+        'Updating local submodule URL to point back to %s',
+        $url));
+
+      $working_directory_cmd->execx(
+        'git config --local submodule.%s.url %s',
+        $name,
+        $url);
+    }
+
+    $this->log(pht(
+      'Submodules initialized for working directory at %s',
+      $working_directory_path));
   }
 
   public function getType() {
@@ -112,19 +652,40 @@
     DrydockLease $lease,
     $type) {
 
-    switch ($type) {
-      case 'command':
-        return $this
-          ->loadLease($resource->getAttribute('lease.host'))
-          ->getInterface($type);
-    }
-
-    throw new Exception(pht("No interface of type '%s'.", $type));
+    return $this
+      ->loadLease($lease->getAttribute('host.lease'))
+      ->getInterface($type);
   }
 
   protected function executeReleaseLease(
     DrydockResource $resource,
-    DrydockLease $lease) {}
+    DrydockLease $lease) {
+
+    if ($lease->getAttribute('cacheOnly')) {
+      $this->log(pht(
+        'Cache-only lease; not releasing related lease'));
+    } else if (!$lease->getAttribute('hostLeaseID')) {
+      $this->log(pht(
+        'Releasing host lease %d',
+        $lease->getAttribute('host.lease')));
+      try {
+        $host_lease = $this->loadLease($lease->getAttribute('host.lease'));
+
+        $host_resource = $host_lease->getResource();
+        $host_blueprint = $host_resource->getBlueprint();
+        $host_blueprint->releaseLease($host_resource, $host_lease);
+
+        $this->log(pht(
+          'Released host lease %d',
+          $lease->getAttribute('host.lease')));
+      } catch (Exception $ex) {
+        $this->log(pht(
+          'Unable to release host lease %d: "%s"',
+          $lease->getAttribute('host.lease'),
+          (string)$ex));
+      }
+    }
+  }
 
   protected function shouldCloseUnleasedResource(
     DrydockAllocationContext $context,
@@ -134,7 +695,67 @@
   }
 
   protected function executeCloseResource(DrydockResource $resource) {
-    // TODO: Remove leased directory
+    $this->log(pht(
+      'Releasing resource host lease %d',
+      $resource->getAttribute('host.lease')));
+      try {
+        $host_lease = $this->loadLease($resource->getAttribute('host.lease'));
+
+        $host_resource = $host_lease->getResource();
+        $host_blueprint = $host_resource->getBlueprint();
+        $host_blueprint->releaseLease($host_resource, $host_lease);
+
+        $this->log(pht(
+          'Released resource host lease %d',
+          $resource->getAttribute('host.lease')));
+      } catch (Exception $ex) {
+        $this->log(pht(
+          'Unable to release resource host lease %d: "%s"',
+          $resource->getAttribute('host.lease'),
+          (string)$ex));
+      }
+  }
+
+  public function getFieldSpecifications() {
+    return array(
+      'host-config' => array(
+        'name' => pht('Host Configuration'),
+        'type' => 'header',
+      ),
+      'host-blueprint' => array(
+        'name' => pht('Host Blueprint'),
+        'type' => 'blueprints',
+        'required' => true,
+        'limit' => 1,
+        'blueprint-type' => 'host',
+        'caption' => pht(
+          'The blueprint which provides hosts that this '.
+          'blueprint will operate on.'),
+      ),
+      'host-platform' => array(
+        'name' => pht('Host Platform'),
+        'type' => 'text',
+        'required' => true,
+        'caption' => pht(
+          'An optional host platform to specify; only used '.
+          'if the host blueprint doesn\'t have a platform '.
+          'specified already (such is the case for '.
+          'preallocated hosts).'),
+      ),
+      'attr-header' => array(
+        'name' => pht('Working Copy Attributes'),
+        'type' => 'header',
+      ),
+      'attributes' => array(
+        'name' => pht('Working Copy Attributes'),
+        'type' => 'textarea',
+        'caption' => pht(
+          'A newline separated list of working copy attributes.  '.
+          'Each attribute should be specified in a key=value format.'),
+        'monospace' => true,
+      ),
+    ) + parent::getFieldSpecifications();
   }
 
+
 }
diff --git a/src/applications/drydock/customfield/DrydockBlueprintCustomFieldBlueprints.php b/src/applications/drydock/customfield/DrydockBlueprintCustomFieldBlueprints.php
new file mode 100644
--- /dev/null
+++ b/src/applications/drydock/customfield/DrydockBlueprintCustomFieldBlueprints.php
@@ -0,0 +1,50 @@
+<?php
+
+final class DrydockBlueprintCustomFieldBlueprints
+  extends PhabricatorStandardCustomFieldPHIDs {
+
+  public function getFieldType() {
+    return 'blueprints';
+  }
+
+  public function renderEditControl(array $handles) {
+    $value = $this->getFieldValue();
+
+    $control = id(new AphrontFormTokenizerControl())
+      ->setUser($this->getViewer())
+      ->setLabel($this->getFieldName())
+      ->setName($this->getFieldKey())
+      ->setDatasource(id(new DrydockBlueprintDatasource())
+        ->setParameters(array(
+          'type' => $this->getFieldConfigValue('blueprint-type'),
+        )))
+      ->setCaption($this->getCaption())
+      ->setValue(nonempty($value, array()));
+
+    $limit = $this->getFieldConfigValue('limit');
+    if ($limit) {
+      $control->setLimit($limit);
+    }
+
+    return $control;
+  }
+
+  public function appendToApplicationSearchForm(
+    PhabricatorApplicationSearchEngine $engine,
+    AphrontFormView $form,
+    $value,
+    array $handles) {
+
+    $control = id(new AphrontFormTokenizerControl())
+      ->setLabel($this->getFieldName())
+      ->setName($this->getFieldKey())
+      ->setDatasource(id(new DrydockBlueprintDatasource())
+        ->setParameters(array(
+          'type' => $this->getFieldConfigValue('blueprint-type'),
+        )))
+      ->setValue(nonempty($value, array()));
+
+    $form->appendControl($control);
+  }
+
+}
diff --git a/src/applications/drydock/phid/DrydockBlueprintPHIDType.php b/src/applications/drydock/phid/DrydockBlueprintPHIDType.php
--- a/src/applications/drydock/phid/DrydockBlueprintPHIDType.php
+++ b/src/applications/drydock/phid/DrydockBlueprintPHIDType.php
@@ -29,6 +29,7 @@
       $blueprint = $objects[$phid];
       $id = $blueprint->getID();
 
+      $handle->setName($blueprint->getBlueprintName());
       $handle->setURI("/drydock/blueprint/{$id}/");
     }
   }
diff --git a/src/applications/drydock/typeahead/DrydockBlueprintDatasource.php b/src/applications/drydock/typeahead/DrydockBlueprintDatasource.php
new file mode 100644
--- /dev/null
+++ b/src/applications/drydock/typeahead/DrydockBlueprintDatasource.php
@@ -0,0 +1,52 @@
+<?php
+
+final class DrydockBlueprintDatasource
+  extends PhabricatorTypeaheadDatasource {
+
+  public function isBrowsable() {
+    return true;
+  }
+
+  public function getBrowseTitle() {
+    return pht('Browse Blueprints');
+  }
+
+  public function getPlaceholderText() {
+    return pht('Type blueprint names...');
+  }
+
+  public function getDatasourceApplicationClass() {
+    return 'PhabricatorDrydockApplication';
+  }
+
+  public function loadResults() {
+    $viewer = $this->getViewer();
+
+    $blueprint_type = $this->getParameter('type');
+
+    $blueprints = id(new DrydockBlueprintQuery())
+      ->setViewer($viewer)
+      ->execute();
+    $blueprints = mpull($blueprints, null, 'getPHID');
+
+    if (count($blueprints) === 0) {
+      return array();
+    }
+
+    $results = array();
+    foreach ($blueprints as $phid => $blueprint) {
+      if ($blueprint_type !== null &&
+        $blueprint->getImplementation()->getType() !== $blueprint_type) {
+        continue;
+      }
+
+      $results[] = id(new PhabricatorTypeaheadResult())
+        ->setName($blueprint->getBlueprintName())
+        ->setURI('/')
+        ->setPHID($phid);
+    }
+
+    return $results;
+  }
+
+}
diff --git a/src/applications/drydock/worker/DrydockAllocatorWorker.php b/src/applications/drydock/worker/DrydockAllocatorWorker.php
--- a/src/applications/drydock/worker/DrydockAllocatorWorker.php
+++ b/src/applications/drydock/worker/DrydockAllocatorWorker.php
@@ -104,6 +104,12 @@
         continue;
       }
 
+      if ($lease->getAttribute('resourceID') !== null &&
+        $candidate->getID() !== $lease->getAttribute('resourceID')) {
+        unset($pool[$key]);
+        continue;
+      }
+
       $blueprint = $blueprints[$candidate->getBlueprintPHID()];
       $implementation = $blueprint->getImplementation();
 
@@ -144,6 +150,12 @@
           continue;
         }
 
+        if ($lease->getAttribute('resourceID') !== null &&
+          $candidate->getID() !== $lease->getAttribute('resourceID')) {
+          unset($pool[$key]);
+          continue;
+        }
+
         $blueprint = $blueprints[$candidate->getBlueprintPHID()];
         $implementation = $blueprint->getImplementation();
 
diff --git a/src/applications/harbormaster/step/HarbormasterLeaseWorkingCopyBuildStepImplementation.php b/src/applications/harbormaster/step/HarbormasterLeaseWorkingCopyBuildStepImplementation.php
new file mode 100644
--- /dev/null
+++ b/src/applications/harbormaster/step/HarbormasterLeaseWorkingCopyBuildStepImplementation.php
@@ -0,0 +1,84 @@
+<?php
+
+final class HarbormasterLeaseWorkingCopyBuildStepImplementation
+  extends HarbormasterBuildStepImplementation {
+
+  public function getName() {
+    return pht('Lease Working Copy');
+  }
+
+  public function getGenericDescription() {
+    return pht(
+      'Obtain a lease on a Drydock working copy of the '.
+      'current buildable for performing builds.');
+  }
+
+  public function execute(
+    HarbormasterBuild $build,
+    HarbormasterBuildTarget $build_target) {
+
+    $settings = $this->getSettings();
+
+    $custom_attributes = DrydockCustomAttributes::parse(
+      $settings['attributes']);
+
+    // Create the lease.
+    $lease = id(new DrydockLease())
+      ->setResourceType('working-copy')
+      ->setAttributes(
+        array(
+          'platform' => $settings['platform'],
+          'buildablePHID' => $build->getBuildablePHID(),
+        ) + $custom_attributes)
+      ->queueForActivation();
+
+    // Create the associated artifact.
+    $artifact = $build->createArtifact(
+      $build_target,
+      $settings['name'],
+      HarbormasterBuildArtifact::TYPE_HOST);
+    $artifact->setArtifactData(array(
+      'drydock-lease' => $lease->getID(),
+    ));
+    $artifact->save();
+
+    // Wait until the lease is fulfilled.
+    // TODO: This will throw an exception if the lease can't be fulfilled;
+    // we should treat that as build failure not build error.
+    $lease->waitUntilActive();
+  }
+
+  public function getArtifactOutputs() {
+    return array(
+      array(
+        'name' => pht('Leased Working Copy'),
+        'key' => $this->getSetting('name'),
+        'type' => HarbormasterBuildArtifact::TYPE_HOST,
+      ),
+    );
+  }
+
+  public function getFieldSpecifications() {
+    return array(
+      'name' => array(
+        'name' => pht('Artifact Name'),
+        'type' => 'text',
+        'required' => true,
+      ),
+      'platform' => array(
+        'name' => pht('Host Platform'),
+        'type' => 'text',
+        'required' => true,
+      ),
+      'attributes' => array(
+        'name' => pht('Required Attributes'),
+        'type' => 'textarea',
+        'caption' => pht(
+          'A newline separated list of required working copy attributes.  '.
+          'Each attribute should be specified in a key=value format.'),
+        'monospace' => true,
+      ),
+    );
+  }
+
+}