Upload performance issues in Proxy mode

Over the last few months I have been receiving intermittent reports from users of slow upload speeds. Recently I conducted some tests to validate the reports and these showed that there was significantly reduced upload performance to my site with Cloudflare in proxy mode vs. when it is in DNS only mode.

I conducted these tests from two locations (Hampshire, UK on a DSL connection and Amsterdam, NL on a hosted server with fast internet connectivity) to eliminate issues specific to the connection and Cloudflare POP location from the results.

From each location I ran the following three times each for HTTP/1.1 and HTTP/2 and averaged the results. I then enabled Cloudflare Proxy for the site and ran the same tests again

The upload.php script simply sends the request body to /dev/null.

dd if=/dev/urandom of=test.dat bs=1M count=10
curl --http2 -w '%{speed_upload}\n' -sf -o/dev/null --data-binary @test.dat https://mysite/upload.php

These were the results I got


In short - without Cloudflare proxy, uploads are completed at around 1.8-2.4Mbps. With it enabled, speeds fall to 0.2-0.8Mbps.

Is this an issue with Cloudflare specific to upload? Is it just “something to expect as a result of the proxying” or is there something going wrong?

Sadly for larger uploads I’m finding my users are getting timeouts so currently I’m using Cloudflare without the proxy on this particular site.

Any further detail needed to help isolate this issue?

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