server-stale-while-revalidate.vcl

# You must set a grace period on any object you put in cache for this to work.

sub vcl_hit {
  if (obj.ttl >= 0s) {
    return (deliver);
  }
  if (obj.ttl + obj.grace > 0s) {
    return (deliver);
  }
  
  # This must return fetch if Varnish version 4/5. This is config for Varnish 6
  return (miss);
}