Connection test for Elastic Full Text Search engine failed during upgrade

Dear Community,

I have a problem upgrading from 7.7.1.1 to 7.7.2.3. I am using the CliUpgrader v.7.7.2.3 (build 81) and the SugarPro-Upgrade-7.7.x-to-7.7.2.3.zip according to the post Upgrade Paths for On-Site Installations.

During the upgrade process the following error occurs:

Wed, 03 Jan 2018 15:24:26 +0100 [Upgrader] - Starting script CheckFTSConfig
Wed, 03 Jan 2018 15:24:26 +0100 [Upgrader] - ERROR: Connection test for Elastic Full Text Search engine failed.  Check your FTS configuration.
Wed, 03 Jan 2018 15:24:26 +0100 [Upgrader] - ERROR: Access Full Text Search configuration under Administration > Search.
Wed, 03 Jan 2018 15:24:26 +0100 [Upgrader] - Finished script CheckFTSConfig
Wed, 03 Jan 2018 15:24:26 +0100 [Upgrader] - ERROR: Pre-upgrade stage failed!

From my point of view everything is fine with our Elastic connection. It is working in global search and the elastic instance responds like expected. Is there a known issue with the elastic client within SugarCRM? We are using an IP address on the local network with non-standard port 9201 for elastic.

Any help is really appreciated! Thanks!

Additional information:

  • Windows Server 2016 64bit
  • Hosted with IIS 10
  • PHP 5.6.22
  • Elastic 2.4.0 / Lucene 5.5.2
_sugarupgrade.log.zip