title: Is it possible to deploy without downtime without disconnecting TCP sockets connected?
body: <p>There is a long connected TCP socket. Up to two clients can connect to a server. In other words, the load is not high. However, once a TCP connection is made, the socket will not be disconnected unless there is an accident, such as a server power down or network failure. Is it possible to reuse an existing TCP socket when restarting the process? I think TCP load balancer like AWS NLB cannot be used since the existing socket won't be moved to a new application. I'd like to have a deployment without downtime, as the system i'm working on is a system that can suffer financial damage when a socket is broken and data is lost. Low-level socket programming is ok.</p>
  
  <p>I have read CloudFlare's <a href="https://blog.cloudflare.com/graceful-upgrades-in-go/" rel="nofollow noreferrer">https://blog.cloudflare.com/graceful-upgrades-in-go/</a> article explaining Nginx's Gracefully Reload mechanism. Since an HTTP server is a server that opens and closes sockets frequently, that article assumes that the server's connection would someday be closed, but my situation is slightly different. So I'm not sure if this can be used.</p>