While working with a few VM's recently I kept getting the following error and FAST would not index anything or return any results:
Failed to connect to {server}:13391 Failed to initialize session with document engine: Unable to resolve Contentdistributor
I trawled through the internet and found lots of things that people had done to try and resolve this. Everything from changing the port number to "13390" instead of "13391" which does NOT work by the way, to replacing the certificate being used by FAST, however none of these worked at all. After some investigation I started to check accounts that were used by SharePoint and their permissions. From "Central Administration" I accessed the "security, then Service Accounts" and checked what account was running the "SharePoint Server Search" service.
As was expected it was set to the "SPSearch" account. So I thought just on the off chance I would check the actual windows service account. To my surprise it was not running as the expected account.
For some reason it was running as the "SPAppPool" account, I remembered then that this environment was installed and configured using the standard "Configuration Wizard" and not the PowerShell scripts I would normally use.
This made sense then why I was seeing the error in the event log that was telling me it was an issue with the "SPAppPool" account.
So I set the service back to the correct account and tried again, however I was still seeing the same issue. So after some investigation and reading I decided that to make 100% sure that everything was configured correctly and in the right context that I would re-run the required PowerShell commands under the context of the "SPSearch" account.
So I first had to launch PowerShell management shell for SharePoint 2010, by holding the "shift" key and right clicking to select "Run as different user"., I then entered the credentials for the "SPSearch" account
I then navigated to: "C:\FASTSearch\installer\scripts" in the loaded PowerShell management window and I then ran the following command
.\SecureFASTSearchConnector.ps1 -certPath "C:\FASTSearch\data\data_security\cert\FASTSearchCert.pfx" -ssaName "FAST Connect" -userName "DOMAIN\SPSearch"
When I got prompted I entered the password that I created for the Certificate during the installation.
It then completed successfully, with a validation message.
In same PowerShell window I then typed the following command to export the STS certificate
$stsCert = (Get-SPSecurityTokenServiceConfig).LocalLoginProvider.SigningCertificate
$stsCert.Export("cert") | Set-Content -encoding byte MOSS_STS.cer
I had to make a note of the path to the certificate which was the location the command was run
Finally in the PowerShell window for FAST Search, I changed to that path: "C:\FASTSearch\Installer\Scripts", then ran the following command
.\InstallSTSCertificateForClaims.ps1 -certPath "C:\FASTSearch\installer\scripts\MOSS_STS.cer"
It completed successfully, showing it had installed the certificate and then restarted the "qrproxy" service.
Once all this was done I was able to get FAST search to crawl and return results. Hope this helps.