Original comment by @droberts195:

The ML results index rollover endpoint will need to do the following:

• Take a results_index_name field as input (which can be shared for the default shared index)
• Check whether it's appropriate to roll that particular index - this can be done using the dry_run argument of the standard rollover API
• If it is then create the new empty index
• Adjust all the read aliases for jobs that have the chosen results_index_name to include the newly created index
• Adjust all the write aliases for jobs that have the chosen results_index_name to point at the newly created index
• All the alias updates can be done atomically in one request