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Olga Maciaszek-Sharma
2020-12-18 17:58:35 +01:00
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@@ -1118,15 +1118,38 @@ public class MyConfiguration {
One type of bean that it may be useful to register using <<custom-loadbalancer-configuration,Custom LoadBalancer configuration>> is `LoadBalancerLifecycle`.
The LoadBalancerLifecycle beans provide callback methods, named `onStart(Request<RC> request)` and `onComplete(CompletionContext<RES, T> completionContext)`, that you should implement to specify what actions should take place before and after load-balancing.
The `LoadBalancerLifecycle` beans provide callback methods, named `onStart(Request<RC> request)`, `onStartRequest(Request<RC> request, Response<T> lbResponse)` and `onComplete(CompletionContext<RES, T, RC> completionContext)`, that you should implement to specify what actions should take place before and after load-balancing.
`onStart(Request<RC> request)` takes a `Request` object as a parameter. It contains data that is used to select an appropriate instance, including the downstream client request and <<spring-cloud-loadbalancer-hints,hint>>. On the other hand, a `CompletionContext` object is provided to the `onComplete(CompletionContext<RES, T> completionContext)` method. It contains the LoadBalancer `Response`, including the selected service instance, the `Status` of the request executed against that service instance and (if available) the response returned to the downstream client, and (if an exception has occurred) the corresponding `Throwable`.
`onStart(Request<RC> request)` takes a `Request` object as a parameter. It contains data that is used to select an appropriate instance, including the downstream client request and <<spring-cloud-loadbalancer-hints,hint>>. `onStartRequest` also takes the `Request` object and, additionally, the `Response<T>` object as parameters. On the other hand, a `CompletionContext` object is provided to the `onComplete(CompletionContext<RES, T, RC> completionContext)` method. It contains the LoadBalancer `Response`, including the selected service instance, the `Status` of the request executed against that service instance and (if available) the response returned to the downstream client, and (if an exception has occurred) the corresponding `Throwable`.
The `supports(Class requestContextClass, Class responseClass,
Class serverTypeClass)` method can be used to determine whether the processor in question handles objects of provided types. If not overridden by the user, it returns `true`.
NOTE: In the preceding method calls, `RC` means `RequestContext` type, `RES` means client response type, and `T` means returned server type.
[[loadbalancer-micrometer-stats-lifecycle]]
=== Spring Cloud LoadBalancer Statistics
We provide a `LoadBalancerLifecycle` bean called `MicrometerStatsLoadBalancerLifecycle`, which uses Micrometer to provide statistics for load-balanced calls.
In order to get this bean added to your application context,
set the value of the `spring.cloud.loadbalancer.stats.micrometer.enabled` to `true` and have a `MeterRegistry` available (for example, by adding https://docs.spring.io/spring-boot/docs/current/reference/html/production-ready-features.html[Spring Boot Actuator] to your project).
`MicrometerStatsLoadBalancerLifecycle` registers the following meters in `MeterRegistry`:
* `loadbalancer.requests.active`: A gauge that allows you to monitor the number of currently active requests for any service instance (service instance data available via tags);
* `loadbalancer.requests.success`: A timer that measures the time of execution of any load-balanced requests that have ended in passing a response on to the underlying client;
* `loadbalancer.requests.failed`: A timer that measures the time of execution of any load-balanced requests that have ended with an exception;
* `loadbalancer.requests.discard`: A counter that measures the number of discarded load-balanced requests, i.e. requests where a service instance to run the request on has not been retrieved by the LoadBalancer.
Additional information regarding the service instances, request data, and response data is added to metrics via tags whenever available.
NOTE: For some implementations, such as `BlockingLoadBalancerClient`, request and response data might not be available, as we establish generic types from arguments and might not be able to determine the types and read the data.
NOTE: The meters are registered in the registry when at least one record is added for a given meter.
TIP: You can further configure the behavior of those metrics (for example, add https://micrometer.io/docs/concepts#_histograms_and_percentiles[publishing percentiles and histograms]) by https://docs.spring.io/spring-boot/docs/current/reference/html/production-ready-features.html#production-ready-metrics-per-meter-properties[adding `MeterFilters`].
== Spring Cloud Circuit Breaker
include::spring-cloud-circuitbreaker.adoc[leveloffset=+1]