Node reuse - Driver

Every session response includes servedBy, the id of the machine that ran it. Pass it as nodeId on a later create to land on the same machine.

const first = await createSession({ country: "US" });
// … work, stop …
const again = await createSession({ nodeId: first.servedBy });

first = create_session(country="US")
# ... work, stop ...
again = create_session(nodeId=first["servedBy"])

When it helps

A site keyed something to the machine. Rare; most keying is by cookies, which profiles handle better.
Reproducing a problem that only happens on one machine.

Rules

nodeId overrides country and type. You get that machine, wherever it is.
If the machine is busy or gone, the request fails. No fallback to another machine.

For most workloads leave nodeId out and let placement pick a machine in the country you asked for.