There isn't much to share. We made numerous attempts to reach out to the customer but never got a response, so we don't know exactly what they were doing.
We don't know for sure it was a 28.8K modem, it just appeared to be, given the speed they uploaded and the slight variances we saw in the speed (if it was a throttled upload, they tend to be pretty rigid in performance).
One of the main things it exposed was that certain libraries we used had buffers in them. We'd proxy the data from the customer to another back end service. By default the library would open the connection to the back end, and wait for the small buffer to fill before sending the data. The back end service would terminate a connection if the connection was open but idle for $x number of seconds.
The user was on the threshold of that timeout. Probably half the time they PUT, they'd be slow enough to trigger that back-end timeout, resulting in them getting a 500. I believe eventually they put a small buffer on the ingestion path too before pushing along to the back end, but given those PUTs could get really large, we couldn't buffer the entire content before sending along.
