HHVM takes more time to initialize than PHP5, because it needs to translate PHP to byte code, analyze the types flowing through the code, and then compile the byte code down to machine code. This process takes a few minutes, but during that time the application server is too slow to serve user requests.
Because this is the case, it is essential to avoid a cold restart of the entire production cluster. We need to have a staggered deployment process that allows us to take servers offline while they are warming up and then bring them back online once they're ready.
To meet these requirements, we need better automation. The current process for adding and removing servers from the pool serving user requests is too slow and too manual.