Package org.apache.curator.framework.state

Class CircuitBreakingConnectionStateListener

java.lang.Object
org.apache.curator.framework.state.CircuitBreakingConnectionStateListener
All Implemented Interfaces:
ConnectionStateListener
public class CircuitBreakingConnectionStateListener extends Object implements ConnectionStateListener

A proxy for connection state listeners that adds circuit breaking behavior. During network outages ZooKeeper can become very noisy sending connection/disconnection events in rapid succession. Curator recipes respond to these messages by resetting state, etc. E.g. LeaderLatch must delete its lock node and try to recreate it in order to try to re-obtain leadership, etc.

This noisy herding can be avoided by using the circuit breaking listener. When it receives ConnectionState.SUSPENDED, the circuit becomes "open" (based on the provided RetryPolicy) and will ignore future connection state changes until RetryPolicy timeout has elapsed. Note: however, if the connection goes from ConnectionState.SUSPENDED to ConnectionState.LOST the first LOST state is sent.

When the circuit is closed, all connection state changes are forwarded to the managed listener. When the first disconnected state is received, the circuit becomes open. The state change that caused the circuit to open is sent to the managed listener and the RetryPolicy will be used to get a delay amount. While the delay is active, the circuit breaker will store state changes but will not forward them to the managed listener (except, however, the first time the state changes from SUSPENDED to LOST). When the delay elapses, if the connection has been restored, the circuit closes and forwards the new state to the managed listener. If the connection has not been restored, the RetryPolicy is checked again. If the RetryPolicy indicates another retry is allowed the process repeats. If, however, the RetryPolicy indicates that retries are exhausted then the circuit closes - if the current state is different than the state that caused the circuit to open it is forwarded to the managed listener.

NOTE: You should not use this listener directly. Instead, set ConnectionStateListenerManagerFactory.circuitBreaking(org.apache.curator.RetryPolicy) in the CuratorFrameworkFactory.Builder.connectionStateListenerManagerFactory(ConnectionStateListenerManagerFactory).

E.g. 

 ConnectionStateListenerManagerFactory factory = ConnectionStateListenerManagerFactory.circuitBreaking(...retry policy for circuit breaking...);
 CuratorFramework client = CuratorFrameworkFactory.builder()
     .connectionStateListenerManagerFactory(factory)
     ... etc ...
     .build();
 // all connection state listeners set for "client" will get circuit breaking behavior

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