[Twisted-Python] Asynchronously initializing objects in twisted.web?

Hi, I wonder, if I have this example program: https://twistedmatrix.com/documents/current/web/howto/using-twistedweb.html#... how do I initialize an external resource (like a dictionary, which is fetched from a database) with asynchronous twisted tools, but before the HTTP server starts listening on its port? The goal here is that the HTTP server shouldn't start until it can fetch the desired data. Of course I can do this in a synchronous way, but it feels so unnatural and bad practice to fetch the same stuff synchronously on initialization and asynchronously when the program/reactor is running (often with different libraries). Thanks,