HEAD /agents doesn't work because app has /agents link. Use GET /ping instead.

lib/Percona/WebAPI/Client.pm

@@ -159,23 +159,6 @@ sub get {
    return $resource_objects;
 }
 
-sub head {
-   my ($self, %args) = @_;
-
-   have_required_args(\%args, qw(
-      link
-   )) or die;
-   my ($link) = $args{link};
-
-   eval {
-      $self->_request(
-         method => 'HEAD',
-         link   => $link,
-      );
-   };
-   return $EVAL_ERROR;
-}
-
 # For a successful POST, the server sets the Location header with
 # the URI of the newly created resource.
 sub post {