gistfile1.php

<?php

// Added to the bottom of Provision_Service_http_pack

  function shell_exec($command) {
    $this->_each_server($this->server->master_web_servers, __FUNCTION__, array($command));
    $this->_each_server($this->server->slave_web_servers, __FUNCTION__, array($command));
  }

myclient_provision.drush.inc.php

<?php

/**
 * After a site is installed, reach out to each web server and verify that the
 * files directory is a symlink to the correct AFS volume.
 */
function drush_myclient_provision_post_provision_install() {
  if (d()->type == 'site' && method_exists(d()->service('http'), '_each_server')) {
    $volume_id = d()->myclient_site_afs_volume_name;
    $site_path = d()->site_path;

    // Remove the files and private directory and any child directories if they exist.
    $command = 'rm -rf ' . escapeshellarg($site_path . '/files') . ' && rm -rf ' . escapeshellarg($site_path . '/private');
    d()->service('http')->shell_exec($command);

    drush_log(dt('Executed @command on remote servers.', array('@command' => $command)), 'notice');
    drush_log(dt('Removed old files directories on remote servers'), 'success');

    // Create symlinks from the old paths to AFS.
    $volume_path = '/afs/myclient/g/web/drupal/' . $volume_id;
    $command = 'ln -s ' . escapeshellarg($volume_path . '/files') . ' ' . escapeshellarg($site_path . '/files') . ' && ' .
      'ln -s ' . escapeshellarg($volume_path . '/private') . ' ' . escapeshellarg($site_path . '/private');
    d()->service('http')->shell_exec($command);

    drush_log(dt('Executed @command on remote servers.', array('@command' => $command)), 'notice');
    drush_log(dt('Created symlinks for files and private directories on remote servers'), 'success');
  }
}