Local Installation: Interviwer app cannot connect to the server over HTTPS

January 9, 2018

Symptoms:
When Interviewer app is trying to connect to the Headquarters application on a local server over the secure http (https) protocol synchronization process fails with an error “NO CONNECTION TO THE SURVEY SOLUTIONS SUPERVISOR. PLEASE MAKE SURE THAT THE WEBSITE IS AVAILABLE”.

The Headquarters application is setup correctly, with a valid security certificate, and in the mobile browser on the Android device users can successfully access it without any errors or warnings.

The Headquarters application is hosted on a server running Windows 2016.

Explanation:
Communication fails due to a bug in one of the external libraries used in Interviewer app. That library breaks when trying to setup a secure connection over http/2 - version 2 of the http protocol.

The error doesn’t happen on 1.1 version, neither when using unsecured http/2.

Starting from Windows 10 desktop and Windows 2016, IIS started supporting (and using by default) http/2 and that is the reason why the users who use this combination secured connection with the application on Windows 2016 encounter the failed communication error.

Solution:
We are working on introducing changes in our code that would remedy this error and once those changes are out, we will update this article and consider the problem resolved.

Meanwhile, workarounds to this problem include:

  • Use Windows 2012.
  • Use http protocol (not recommended for real data-collection but may be a quick solution during initial testing).
  • Disable http/2 in Windows 2016 and use http/1.1 instead.

You can disable using http/2 for https connections by adding  DWORD value with name EnableHttp2Tls to HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\HTTP\Parameters and setting it to 0.

The changes will take effect after server is restarted.

WARNING: Serious problems might occur if you modify the registry incorrectly so only attempt to do above if you are comfortable with manually editing registry have a backup of the registry and/or whole system.