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The new service performs failure detection by periodically pinging endpoints. The set of pinged endpoints can be dynamically extended and shrinked. To learn about liveness of endpoints, user of the service registers a listener and chooses a threshold - a duration of time which has to pass since the last successful ping in order to mark an endpoint as dead. When an endpoint responds it's immediately marked as alive. Endpoints are identified using abstract integer identifiers. The method of performing a ping is a dependency of the service provided by the user through the `pinger` interface. The implementation of `pinger` is responsible for translating the abstract endpoint IDs to 'real' addresses. For example, production implementation may map endpoint IDs to IP addresses and use TCP/IP to perform the ping, while a test/simulation implementation may use a simulated network that also operates on abstract identifiers. Similarly, the method of measuring time is a dependency provided by the user using the `clock` interface. The service operates on abstract time intervals and timepoints. So, for example, in a production implementation time can be measured using a stopwatch, while in test/simulation we can use a logical clock. The service distributes work across different shards. When an endpoint is added to the set of detected endpoints, the service will choose a shard with the smallest amount of workers and create a worker that is responsible for periodically pinging this endpoint on that shard and sending notifications to listeners. Endpoints can be added or removed only through the shard 0 instance of the service and shard 0 is responsible for coordinating the endpoint workers. Listeners can be registered on any shard.