anchor.diff:      .threshold = 3;
     }
   }
  +
  +backend designprinciples_<%= i %> {
  +  .host = "<%= host %>";
  +  .port = "8085";
  +  .host_header = "designprinciples.<%= govuk_platform %>.alphagov.co.uk";
  +  .probe = {
  +    .url = "/";
  +    .interval = 5s;
  +    .timeout = 1s;
  +    .window = 5;
  +    .threshold = 3;
  +  }
  +}
  +
   <% end %>
   
   director frontend round-robin {
  
positive.code:   <% frontend_hosts.count.times do |i| %>
    {
    .backend = smartanswers_<%= i %>;
    }
    <% end %>
  }
  
negative.code:     set req.backend = whitehall;
    } else if (req.url ~ "^/maternity(\.xml|\.json|\.ics)?(\?.*|)$|^/paternity(\.xml|\.json|\.ics)?(\?.*|)$") {
      set req.backend = planner;
    } else if (req.url ~ "^/designprinciples") {
      set req.backend = designprinciples;
    } else {
      set req.backend = frontend;
    }
  