Why do you want both processes to accept? That sounds like a bad thing, since you can't test to make sure the new server came up right. You have no way to make sure you're hitting the new process, until you tell the old to stop accepting. And you want to be able to recover if the new process doesn't work.
What I'd suggest is to add a "stop accepting" and "start accepting" signal, maybe a URL route that checks that it came from localhost or something and sets/clears a flag. If the flag is set, the mainloop skips all calls to accept().
So the full set up is, first the old process stops accepting, but keeps the listening socket open, so new connections queue in the kernel. Then you start the new process and make sure it works. Then you shut down the old process. If the new process doesn't work (e.g., accepts connections and returns 500s or something), then you've lost some requests, but the old process is still around. So you can signal it to start accepting again.
Maybe this is overengineering, but the case I'm worried about is where something in the state of the old process is important (it has an open database connection, it has a module loaded into memory that got corrupted/deleted on disk, etc.). So if you shut down the old process before you test the new one, you have no guarantee you can get the old process back up if you need it. You may have lost the node entirely.
What I'd suggest is to add a "stop accepting" and "start accepting" signal, maybe a URL route that checks that it came from localhost or something and sets/clears a flag. If the flag is set, the mainloop skips all calls to accept().
So the full set up is, first the old process stops accepting, but keeps the listening socket open, so new connections queue in the kernel. Then you start the new process and make sure it works. Then you shut down the old process. If the new process doesn't work (e.g., accepts connections and returns 500s or something), then you've lost some requests, but the old process is still around. So you can signal it to start accepting again.
Maybe this is overengineering, but the case I'm worried about is where something in the state of the old process is important (it has an open database connection, it has a module loaded into memory that got corrupted/deleted on disk, etc.). So if you shut down the old process before you test the new one, you have no guarantee you can get the old process back up if you need it. You may have lost the node entirely.