What is the best way to send notifications to customers of an online store (and not only)?

Question

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For example, when placing an order, you need to generate a pdf invoice, send it to the client, send a notification to the store operator, courier, and more SMS. What is the best way to do this? At the time of order or via cron? If cron, then with what periodicity.

Answer 1

Send to the queue on the order processing server.
There, your server (software) already processes the queue element and performs the necessary actions: it generates an invoice and sends it to the client, sends notifications and SMS.
Pros - can be moved to a separate platform so that it does not interfere with sales.
Cons - with a large stream from the site, the delay can increase significantly.
In general, read about rabbit mq, for example.