Everyone knows serious programs must make data durable. You persist data on disk or in a database so it doesn’t disappear the second your program crashes or your server is restarted. But we also take it for granted that programs themselves aren’t durable. When you restart your server, your data might be safe in the database, but any programs you were running are gone, and if you want them back, you have to restart them yourself.Now, restarting your programs might be fine if they’re short-lived a...