Suppose you’re writing a simple service: it handles inbound requests from your users, but doesn’t hold any data itself. This means that in order to handle any inbound requests it needs to refer to a backend to actually fetch whatever is required. This is a great feature as it means your service is stateless — it’s easier to test, simpler to scale, and typically easier to understand. In our story, you’re also lucky as you only handle a single request at a time with a single worker doing the work.
Your service diagram might look like this: