Over time, Lemmy instances are going to keep aquiring more, and more data. Even if, in the best case, they are not caching content and they are just storing the data posted to communities local to the server, there will still be a virtually limitless growth in server storage requirements. Eventually, it may get to a point where it is no longer economically feesible to host all of the infrastructure to keep expanding the server’s storage. What happens at this point? Will servers begin to periodically purge old content? I have concerns that there will be a permanent horizon (as Lemmy becomes more popular, the rate of growth in storage requirements will also increase, thereby reducing the distance to this horizon) over which old - and still very useful - data will cease to exist. Is there any plan to archive this old data?
As for the data transfer costs, any network data originating from AWS that hits an external network (an end user or another region) typically will incur a charge. To quote their blog post:
So you won’t be charged for incoming federated content, but serving content to the end user will count as traffic exiting AWS. I am not sure of your exact setup (AWS pricing is complex) but typically this is charged. This is probably negligible for a single-user instance, but I would be careful serving images from your instance to popular instances as this could incur unexpected costs.