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Comment by dividuum | Hacker News Reader

Can't help with how to implement this, but just to be sure: You should be able to use the same port in multiple instances if you bind those with SO_REUSEPORT. A quick search points to https://github.com/libp2p/go-reuseport for an implementation. Now you just need a mechanism to drain the old process.

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Rough psuedocode to do this with the built-in http.Server where startServer(..) would use the reuseport library to create the listener so multiple servers can listen within the same process:

  func reloadConfig(config) {
    if newServer, err := startServer(config); err != nil {
      // gracefully shutdown previous server
      // no new connections will go to old server
      oldServer.Shutdown(...)
      oldServer = newServer
    }
  }

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