A service registry must stop returning instances that have disappeared, while still allowing live instances to renew their leases and temporarily leave traffic without unregistering.
Design a ServiceRegistry class:
ServiceRegistry(int leaseTtl) creates an empty registry with a fixed lease duration.addInstance(service, instanceId, zone, now) adds a ready instance and returns false when that active instance id already exists.heartbeat(instanceId, now) renews a live instance from now.setReady(instanceId, ready, now) changes whether a live instance may receive traffic without renewing its lease.deregister(instanceId, now) removes a live instance immediately.discover(service, preferredZone, now) returns eligible instance ids.
Times within one object are nondecreasing. Before every operation, expire all entries satisfying:
An expired instance cannot be revived by a heartbeat, readiness change, or deregistration. Its id may be registered again as a new entry. Active instance ids are globally unique across services.
Discovery includes only live, ready instances of the requested service. Return preferred-zone ids first, followed by other zones, with each group sorted lexicographically.
Example 1:
p1 is preferred while it is ready. Its readiness update removes it from discovery but does not renew or delete its registration.
Example 2:
The renewal at time 8 keeps the instance live through times below 18. It expires exactly at time 18.
Constraints
1 <= leaseTtl <= 10^9- Names and ids contain
1 to 40 printable non-space characters. 0 <= now <= 10^9, and times are nondecreasing within one object.- At most
500 live registrations and 10^4 total operations exist per object.
Build a Lease-Based Service Registrymedium