An instance proves it's still alive by sending a heartbeat: a periodic ping that refreshes its last-seen time, resetting its TTL. This is the mechanism that keeps a busy instance in the pool and lets a crashed one fall out automatically: no heartbeat, no refresh, and it expires. A heartbeat for an instance the registry has never seen is meaningless and should be rejected.
Add heartbeats:
heartbeat(service, instance_id, now): if the instance is registered, update its last-seen to now and return True; otherwise return False.class ServiceRegistry:
def __init__(self, ttl=10):
self.ttl = ttl
self.instances = {}
self._rr = {}
def register(self, service, instance_id, now):
self.instances.setdefault(service, {})[instance_id] = now
def healthy(self, service, now):
svc = self.instances.get(service, {})
return sorted(i for i, last in svc.items() if now - last <= self.ttl)
def heartbeat(self, service, instance_id, now):
"""Refresh a known instance's TTL; reject unknown instances."""
svc = self.instances.get(service, {})
# TODO: svc holds this service's instance ids mapped to their last-seen
# times. Only an id already present there may beat: refresh its
# last-seen stamp to now and report True. An id the registry has never
# registered gets False and no change.
pass
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An instance proves it's still alive by sending a heartbeat: a periodic ping that refreshes its last-seen time, resetting its TTL. This is the mechanism that keeps a busy instance in the pool and lets a crashed one fall out automatically: no heartbeat, no refresh, and it expires. A heartbeat for an instance the registry has never seen is meaningless and should be rejected.
Add heartbeats:
heartbeat(service, instance_id, now): if the instance is registered, update its last-seen to now and return True; otherwise return False.Press Run Tests or ⌘↩ to check your solution.