何时在长时间运行的Go程序中释放资源？

I'm building a chat server using Go and Socket.io hence the server would be running indefinitely. There are multiple resources which I need allocated upon the start of the program such as the database connection, redis connection, etc.

Now I'm wondering when all these connections should be released (closed)? Can I use defer in the main function? Does that close them when main reaches its end? Or should I just leave 'em open since the program will not exit on its own accord?

One thing I tend to do is this:

func main() {
    if err := run(); err != nil {
        log.Fatal(err)
    }
}

func run() error {
    // Do stuff here
}

In run you can then defer as you are used to. However, in a long-running program like a server, IMO it's fine to just exit: The OS will clean up all resources taken up by the process automatically and whatever database or backend you have a connection to, has to be able to handle the process dying unexpectedly anyway. This is called "crash-only software".

For tests, you should build your code in a way that it doesn't depend on global state - e.g. have a struct that has fields for the database connections etc. Make the business logic a method on that struct (or a function taking it). You can then in your main populate such a struct and call its methods. And for testing, you can populate a struct, call its methods for whatever tests you want to do and then tear down the connections at the end of your test.