I found and fixed a big performance limitation in the meek-azure transport. If you tried meek-azure before, but it was too slow, give it another try!
meek-azure has always seemed slower than the other two backends, and I recently spent the time to figure out why. It was a lack of persistent HTTP connections between the Azure host and the Tor bridge. Every single HTTP request was doing a complete TCP and TLS handshake. This of course increased latency, but the bottleneck was actually CPU on the bridge, as it tried to cope with all those TLS handshakes. Here is the commit that causes connections to be shared and reused: https://gitweb.torproject.org/pluggable-transports/meek.git/commit/?id=e06bc...
This issue did not affect meek-google because the App Engine URL fetch API reuses HTTP connections transparently. It did not affect meek-amazon because the CloudFront CDN does its own connection reuse.
Usage on meek-azure has already increased in the past few days since I started testing the change. I attached a graph that shows the all-time bandwidth history of the bridge. https://globe.torproject.org/#/bridge/AA033EEB61601B2B7312D89B62AAA23DC3ED8A...
David Fifield
