Execution Pairs

An execution pair consists of:

1. Main Actor $A_{m,i}$

   • Executes the assigned task $T_i$.

   • Monitors the state of the fallback actor $A_{f,i}$.

2. Fallback Actor $A_{f,i}$

   • Monitors the main actor $A_{m,i}$.

   • Takes over if the main actor fails $S(A_{m,i}) = \text{failed}$.

   • Notifies the orchestration layer to assign a new fallback actor.

The state of an actor $S(A)$ can either be:

• Active: The actor is performing its assigned task.

• Failed: The actor is unable to complete the task.

The state of an execution pair $P_i$ is considered operational if at least one actor in the pair is active: $[ S(P_i) = \text{operational} \iff S(A_{m,i}) = \text{active} \vee S(A_{f,i}) = \text{active}. ]$ If both actors in the pair fail, the orchestration layer reassigns both roles.