HA Decision Process

Hello friends, I would like to better understand the decision process of an active and stanby system in the HA process. What would be the criterion for deciding which element will become active in an initial configuration of HA, and the tie-breaking criteria if any. I looked for details on the subject but did not find it and I decided to use an article.

                  I would also like to understand if it is possible and how to configure a preempt so that if a failover occurs, the element that is outside becomes active when it returns up.

                  Sérgio Pontes