Several instances of a program can run on multiple machines in a network. One of the instances is in the role of the master.
Usually, the software can decide much more optimally which one to become the master, then a user could. However, to be prepared for exceptional situations we didn't anticipate, or to allow more control to users who are absolutely sure they know what they are doing, the users will be able to override this automatic decision and manually lock in one of the devices as master.
The most straightforward way to solve this would be two checkboxes.
If the automatic option is chosen, the other one is disabled, and it will update itself automatically, as its status can change depending on system load, etc.
Would this cause confusion? In that case, if automatic mode is selected, the other checkbox could be hidden completely, and the state shown as a label instead.
Alternatively, as setting another device as master manually would remove that status from the previously assigned one, a button "assign this device as master" (hidden or disabled if automatic mode is on) might be better than a checkbox, but that would make the UI cluttered, with 3 different elements (a button, a checkbox, and a label)
How are similar situations usually resolved?