WebPageTest Private - 'no successful results'

I recently configured a new private WebPageTest instance on AWS to use SSL provided by Let's Encrypt, using EFF's awesome CertBot.

When running my first set of tests I noticed big delays (multiple minutes per test) and when the tests finally completed they all reported The test completed but there were no successful results..

A quick look at the access log showed that the agents were getting jobs, but not submitting the results back to the server. I saw a bunch of HTTP 301 responses to the workdone POSTs:

POST /work/workdone.php?run=1... HTTP/1.1" 301 178 "-" "python-requests/2.22.0"

Seeing the 301 responses (and no subsequent 200s) made me realise that CertBot had added a default redirect from port 80 to port 443 to my nginx config (found at /etc/nginx/sites-enabled/default for the WebPageTest AMI).

server {
    if ($host = private.wpt.host) {
        return 301 https://$host$request_uri;
    } # managed by Certbot
       listen 80;
       server_name private.wpt.host;
    return 404; # managed by Certbot
}

Simply commenting out this server block to remove the redirect and bouncing the nginx server immediately resolved the issue. CertBot does ask if it should add the redirect, so simply saying no during configuration would have solved the issue! It would be trivial to allow test agents to communicate on :80 based on the workdone path to get the best of both worlds.

If that is not the cause of your issue, it may be caused by the use of 64-bit windows clients which cannot do traffic shaping using dummynet. Simply adding connectivity=LAN to locations.ini for the test locations should resolve the issue.