> Order confirmation emails and sms messages are triggered by the order submission, and again usually sent off to a 3rd party bulk email or SMS service. Twilio or Campaign Monitor or Mailchimp will have queues and retry mechanisms, but again the website devs are just firing off an API call to some 3rd party that's dealing with that.
In my case, I need to compile templates for the e-mails to be sent, which is somewhat slow. Even if I have an in memory cache for the compiled templates that can then be quickly filled in with actual data, I don't want to make the first user to request them after a restart/flush wait like 4-7 extra seconds upon clicking on the confirm order button (in addition to any other 3rd party calls, checking payment status etc.).
Ergo, I need to carry the actual e-mail preparation logic (regardless of whether I send it myself, or use a 3rd party service) out into a separate thread. The problem then is that I most likely don't want to create a new thread for every e-mail to be processed, so I need a queue for the requests and one or multiple worker threads. There is functionality for this in the stack I'm using so no big deal, except I can't pass live DB entities across threads, so I also need to serialize the data before passing it off to the queue and deserialize it inside of the queue (or just pass some IDs and do DB calls within the queue).
Essentially I've created a simple queue system in the app code, since processing that data definitely shouldn't make the user wait on it. I can see why some might also go the extra step and opt for something like RabbitMQ, since at the end of the day my queue system is likely to be way more barebones than something that's been around for years. But until a certain point, YAGNI.
