Not sure if you’ve ever suffered from this problem, but if you have it can be puzzling as to what is causing it.
From what I’ve found out versions of SharePoint 2013, before the November 2014 CU have an issue that can cause the following registry key to become corrupt.
HKLM\SOFTWARE\Microsoft\Shared Tools\Web Server Extensions\15.0\secure\ConfigDB
This causes your WFE or Application server to then act as though it has been removed from the SharePoint farm.
Any attempt to run the PSConfig.exe (via powershell) or the Product’s and technologies config wizard to join the server back to the farm ends up with an error message either on the console or in the PSCDiag’s file in your logs folder, with a stack trace that looks similar to.
System.ArgumentNullException: Value cannot be null.
Parameter name: server
at Microsoft.SharePoint.Administration.SPSqlConnectionString.GetSqlConnectionString(String server, String failoverServer, String instance, String database, String userName, String password, String connectTimeout)
at Microsoft.SharePoint.Administration.SPSqlConnectionString..ctor(String connectionString)
at Microsoft.SharePoint.PostSetupConfiguration.InitializeTask.Validate(Int32 nextExecutionOrder)
at Microsoft.SharePoint.PostSetupConfiguration.TasksQueue.Validate(Boolean useDefaultExecutionOrder)
What is happening here, is that the details of the connection string to the config DB are lost and the key in the registry end’s up with just the “ConnectionTimout=XXX” value rather than the full string that should read something like “Data Source=SQLServer;Initial Catalog=SP_Config;Integrated Security=True;Enlist=False;Pooling=True;Min Pool Size=0;Max Pool Size=100;Connect Timeout=45”
I believe the issue is related to a non thread safe dictionary object being used to rebuild the connection string this rebuild process can occur during an APP Pool recycle.
Their appears to be a fix in the November 2014 CU that resolves the problem, so if you are experiencing issues with the registry key becoming corrupt, you have two options.
Either deploy November 2014 CU or later, or if this isn’t feasible due to the complexities of updating multiple production servers, you can remove the write permissions of all users on the registry key, so they can read it, but not be able to update it.
This later step is a work around, and may cause issues if you attempt to remove and re-add the server to another SharePoint farm in future, but it will prevent the issue from re-occurring until you can update your SharePoint 2013 platforms with the appropriate or later CU.
Thanks for reading.