An attempt to register DB2 z/OS or Informix with ArcGIS Server 10.5 or a later release, fails with the error:
The connection property set was missing a required property or the property value was unrecognized. Cannot connect to database because the database client software failed to load. Be sure the database client software is installed and configured correctly.
The option to register DB2 z/OS and Informix databases with an ArcGIS Server site before publishing is no longer available.
Create a service definition (.sd) file and use it to publish a service. The .sd file is a stand-alone file that stores the information necessary to publish to an ArcGIS Server site.
When creating the service definition file, do not include the data referenced by your GIS resource. To do that, make sure that the include data in service definition when publishing option is not checked when creating the file. Once published, the service references the data in your database.
See Create a service definition in ArcMap for instructions on creating a service definition file. See Publish a service definition to the server in ArcMap for instructions on publishing the service definition file.