A service registry maps each service name to the set of running instances, each identified by an id and remembered by the time it was last seen. An instance stays "healthy" only for a time-to-live (TTL) window after its last sighting, if that window lapses without contact, it's presumed dead. Because tests can't rely on wall-clock time, every call takes an explicit now.
Build registration and the health check:
register(service, instance_id, now): record the instance under its service with last_seen = now.healthy(service, now): return the sorted ids whose last sighting is within ttl of now (i.e. now - last_seen <= ttl).class ServiceRegistry:
def __init__(self, ttl=10):
self.ttl = ttl
self.instances = {} # service -> {instance_id: last_seen}
self._rr = {}
def register(self, service, instance_id, now):
"""Record (or refresh) an instance's last-seen time."""
# TODO: self.instances.setdefault(service, {})[instance_id] = now
pass
def healthy(self, service, now):
"""Sorted ids seen within the TTL window."""
svc = self.instances.get(service, {})
# TODO: return sorted(i for i, last in svc.items() if now - last <= self.ttl)
pass
The editor and the test runner need a wide screen. Open this page on a desktop browser and your progress will be waiting.
A service registry maps each service name to the set of running instances, each identified by an id and remembered by the time it was last seen. An instance stays "healthy" only for a time-to-live (TTL) window after its last sighting, if that window lapses without contact, it's presumed dead. Because tests can't rely on wall-clock time, every call takes an explicit now.
Build registration and the health check:
register(service, instance_id, now): record the instance under its service with last_seen = now.healthy(service, now): return the sorted ids whose last sighting is within ttl of now (i.e. now - last_seen <= ttl).Press Run Tests or ⌘↩ to check your solution.