 the subsets are defined, the Envoy configuration generated by Pilot would refer to non-existent upstream pools. This results in HTTP 503 errors until all configuration objects are available to Pilot.</p><p>To make sure services will have zero down-time when configuring routes with subsets, follow a &ldquo;make-before-break&rdquo; process as described below:</p><ul><li><p>When adding new subsets:</p><ol><li><p>Update <code>DestinationRules</code> to add a new subset first, before updating any <code>VirtualS