Joining machines to an ArcGIS GIS Server 10.5 site after upgrading fails with "Unable to access directory path '/relational-datastore-types' on the shared config-store"

Description

After upgrading to ArcGIS GIS Server 10.5, joining additional machines to an ArcGIS Server site (single or multi-node) using a network path for the configuration store fails with the following error: 

Error:   
Unable to access directory path '/relational-datastore-types' on the shared config-store.

This issue occurs in the following cases:

• After an upgrade, joining a site or adding a machine to a site using a newly installed ArcGIS 10.5 machine
• After an upgrade, joining a site or adding a machine to a site using an ArcGIS Server machine upgraded to ArcGIS 10.5

This issue does not occur in the following cases:

• Upgrading single or multi-node sites (all operations, except Add/Join, work as expected.)
• Upgrading a single machine site with a local path to the config-store, editing the config-store path to a network path, and following the Add machine and Join site workflows
• All upgrades from earlier versions (not including ArcGIS 10.5) to ArcGIS 10.5.1 or newer (single, multi-node, or local/shared path)

Cause

The host ArcGIS Server site is upgraded to ArcGIS 10.5 from an earlier version. ArcGIS Server searches for a path to the /relational-datastore-types folder, which is unintentionally added to the configuration store path in ArcGIS Server 10.5. This folder is not in the configuration store root path for newer versions.

Note:
This issue does not occur when upgrading from an earlier version to ArcGIS Server 10.5.1 or newer.

Workaround

1. Create a new folder at the folder path below in the ArcGIS Server configuration store folders.

   ...\arcgisserver\config-store\'relational-datastore-types

2. Grant permissions to this folder for the ArcGIS Server service account (domain account).
3. Rejoin the site.

Note:   
It is recommended to delete the relational-datastore-types folder before upgrading to ArcGIS Server 10.5.1 or later from ArcGIS for Server 10.5 to ensure there is no extra folder left in ArcGIS 10.5.1 or later releases.