Aegir Serves 404 error during Migrate task before Varnish is restarted

I migrated a site from one platform to another.  In the process, the site went down with a 404 not found error from Apache.  When the Migrate task completed, Apache (not Drupal) still threw a 404 error.  Post 8080 (Apache, behind Varnish) delivered the page.  So I restarted varnish and the site began responding again on port 80.

 

Hmmm...  Should Varnish be restarted as part of the Migrate task?  Why have I never experienced this with any other Migrate tasks?