Add health indicator for Hystrix

[wjam]

The health of the Hystrix breakers should be reported as part of the health actuator; see http://java.dzone.com/articles/hystrix-and-spring-boots for an example.

[cdupuis]

Very nice idea. Thanks for creating this.

[spencergibb]

I would not recommend using out of service if circuit breakers are open. That is the point of Hystrix that the service does not go out of service.

[dsyer]

Also there are already a bunch of metrics (in /metrics) from Hystrix, so if anyone wants to create a health indicator from them it should be easy (as long as per Spencer's comment) the status is UP by default when the circuit is open.

[cdupuis]

@spencergibb if the circuit is open, doesn't that mean the backend service is OUT_OF_SERVICE? That shouldn't indicate the caller is OUT_OF_SERVICE.

Therefore setting the entry for the backend service to OUT_OF_SERVICE in the result of the HealthIndicator would be fine, wouldn't it?

[cdupuis]

To illustrate: A -> Hystrix -> B

Now if the Hystrix circuit to B is open the result of a call to /health on A could return the following:

{
  "status" : "UP",
  "B" : {
    "status" : "OUT_OF_SERVICE"
    }
  }
}

or instead of using OUT_OF_SERVICE introduce a new CIRCUIT_OPEN status.

[dsyer]

That makes sense. It's just the caller (the aggregate status) that should remain "UP".

[dsyer]

There are some crossed wires here as well though. Hystrix itself is not aware of services (that's Ribbon, which confusingly has its own circuit breaker, and publishes metrics to gauge.servo.ZoneStats_CircuitBreakerTrippedCountetc.). But the Hystrix circuits are also visible (e.g. in the customers appgauge.hystrix.HystrixCommand.StoreIntegration.getStoresByLocationLink.rollingCountShortCircuited=2`).

[cdupuis]

This is now available in d715ec5.