An affinity strategy gives each portunus node (cluster member) a score for a key, and portunus_machine succession promotes the highest-scoring contender. Ties are broken in favor of the node that joined the succession queue first.

Two strategies are supported:

• deterministic: a pure function of the key and the cluster members, so every node computes the same ranking. Built-in variants: fifo, pinned, preferred, hash
• dynamic: a node scores itself from local dynamically calculated state such as metrics (load, resource consumption, etc). Built-in variants: metric, random

Affinity strategies are passed around as a spec() that carries a short name (fifo, pinned, random, and so on). To use a custom module, pass a {Module, Args} tuple where Module implements the kind/0 and score/3 callbacks.