Varnish has a keep time that allows you to hold a 'dead' object for ttl+X for exactly this reason. You server it for so many seconds whilst under load while a s

Varnish has a keep time that allows you to hold a 'dead' object for ttl+X for exactly this reason. You server it for so many seconds whilst under load while a single origin request goes and grabs the data. It's a really solid way to shed load and avoid dropping so many connections at once and then getting slammed on retry.