This answer will vary depending on what you are building. Web app? Language/framework? As far as not dropping in-progress requests, most web sites have multipl

This answer will vary depending on what you are building. Web app? Language/framework? As far as not dropping in-progress requests, most web sites have multiple servers with an haproxy instance that redirects among them. You can deploy to only one box at a time, and haproxy can direct visitors to the boxe(s) that aren't in the middle of being upgraded. There is no generalized answer to your larger question though. Many frameworks and architectures have different deploying methodologies because of their unique nuances. If you share what you're building on, I'm sure many folks here can direct you towards some best practices/how-tos.