You can associate your project fields to custom fields now in Data Center instances too! So, now, we are fully compatible with Data Center instances, there is no change between using Profields on Server / Data Center instances.
Calculated fields cannot use this feature
It is not possible to associate a project field to a custom field on Cummulative Issue Field nor Script Field because these project fields may cause slowdown by its calculated nature.
Custom fields map project fields values
It is very important to remember that every associated custom field get it's value from the project field. For that reason, both must be synchronized to have expected results on your JIRA workflow. This synchronization is made by a project fields update process.
Custom field details
When an association is saved, a custom field is created with the same name and description of the project field. If a project field changes its name or description, the associated custom field will change it automatically too.
The custom field will have locked state, Locked custom field cannot be deleted by any user. The associated custom field will be deleted when the project field become it too.
Although the custom field is locked, you may modify the screens where you can see its information. This configuration should be do it like in any other custom field.
Using custom fields
The process to associate a project field is really simple. You have to enter in Project Fields page, create a new project field or edit one of them and then select the custom field association option.
Step 1 - Navigate to Project Fields page
Step 2 - Create a new project field or edit one created before (only supported fields)
Step 3 - Select the custom field association option
When a project field has an associated custom field, its visibility must be for all users. At the moment, the custom field is visible for all users, its context is global, this is the reason of that restriction.