Functional stability has been proposed as a per-function reliability concept for edge computing, in which the unit of analysis is the individual service rather than the whole system and the binary working/failed evaluation is replaced by a continuous quality function with per-function thresholds. Verifying these properties for a concrete edge orchestrator, migration policy, or distributed inference service requires a constructive method. This article connects functional stability to the direct Lyapunov method. The strong form is characterized through positive invariance of the admissible region; the weak form is connected to uniform ultimate boundedness and input-to-state stability with analytical recovery-time bounds. Switched dynamics from service migration and node failover are treated via common Lyapunov functions. Finite-horizon variants address mission-bounded edge workloads.

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