If every action in a cloud service had to be instantly billable, it would just about double the complexity and cost of every operation. For example, fetching a

If every action in a cloud service had to be instantly billable, it would just about double the complexity and cost of every operation. For example, fetching a blob from S3 would also need to insert the read activity into some realtime billing database AND check if you've exceeded budget. This ends up coupling everything into your billing system and makes the billing system much more active. Instead what cloud providers do is cheaply write an activity log to some async queue system. Eventually (hours later) those logs get aggregated into a central location and a bulk usage levels get updated onto your account. This is much cheaper to do and keeps everything decoupled.