One thing I am not really sure about is if we need a configuration switch for hold/reject behavior. e.g. for Undertow the request holding behavior is very developer friendly, as it means they can just hit refresh in their browser and as soon as the redeployment is done the page will display, however I am worried that it might not be ideal for load balancers that may prefer a quick error response that could then be attempted on another node (although if mod_cluster is not sending out availability till the deployment is 100% complete this may not be a big deal).