MethodBuilder
is a collection of APIs for client configuration at
a higher level than the Finagle 6 APIs while improving upon the deprecated
ClientBuilder.
MethodBuilder
is a collection of APIs for client configuration at
a higher level than the Finagle 6 APIs while improving upon the deprecated
ClientBuilder. MethodBuilder
provides:
All of these can be customized per method (or endpoint) while sharing a single
underlying Finagle client. Concretely, a single service might offer both
getOneTweet
as well as deleteTweets
, whilst each having
wildly different characteristics. The get is idempotent and has a tight latency
distribution while the delete is not idempotent and has a wide latency
distribution. If users want different configurations, without MethodBuilder
they must create separate Finagle clients for each grouping. While long-lived
clients in Finagle are not expensive, they are not free. They create
duplicate metrics and waste heap, file descriptors, and CPU.
Given an example IDL:
exception AnException { 1: i32 errorCode } service SomeService { i32 TheMethod( 1: i32 input ) throws ( 1: AnException ex1, ) }
This gives you a Service
that has timeouts and retries on
AnException
when the errorCode
is 0
:
import com.twitter.conversions.DurationOps._ import com.twitter.finagle.ThriftMux import com.twitter.finagle.service.{ReqRep, ResponseClass} import com.twitter.util.Throw val client: ThriftMux.Client = ??? val svc: Service[TheMethod.Args, TheMethod.SuccessType] = client.methodBuilder("inet!example.com:5555") .withTimeoutPerRequest(50.milliseconds) .withTimeoutTotal(100.milliseconds) .withRetryForClassifier { case ReqRep(_, Throw(AnException(errCode))) if errCode == 0 => ResponseClass.RetryableFailure } .newServiceIface("the_method") .theMethod
Defaults to using the StackClient's configuration.
An example of setting a per-request timeout of 50 milliseconds and a total timeout of 100 milliseconds:
import com.twitter.conversions.DurationOps._ import com.twitter.finagle.thriftmux.MethodBuilder val builder: MethodBuilder = ??? builder .withTimeoutPerRequest(50.milliseconds) .withTimeoutTotal(100.milliseconds)
Retries are intended to help clients improve success rate by trying failed requests additional times. Care must be taken by developers to only retry when it is known to be safe to issue the request multiple times. This is because the client cannot always be sure what the backend service has done. An example of a request that is safe to retry would be a read-only request.
Defaults to using the client's ResponseClassifier to retry failures marked as retryable. See withRetryForClassifier for details.
An example of configuring classifiers for ChannelClosed and Timeout exceptions:
import com.twitter.finagle.service.ResponseClassifier._ import com.twitter.finagle.thriftmux.MethodBuilder val builder: MethodBuilder = ??? builder .withRetryForClassifier(RetryOnChannelClosed.orElse(RetryOnTimeout))
A com.twitter.finagle.service.RetryBudget is used to prevent retries from overwhelming
the backend service. The budget is shared across clients created from
an initial MethodBuilder
. As such, even if the retry rules
deem the request retryable, it may not be retried if there is insufficient
budget.
Finagle will automatically retry failures that are known to be safe to retry via com.twitter.finagle.service.RequeueFilter. This includes WriteExceptions and retryable nacks. As these should have already been retried, we avoid retrying them again by ignoring them at this layer.
Additional information regarding retries can be found in the user guide.
The classifier is also used to determine the logical success metrics of the method. Logical here means after any retries are run. For example should a request result in retryable failure on the first attempt, but succeed upon retry, this is exposed through metrics as a success. Logical success rate metrics are scoped to "clnt/your_client_label/method_name/logical" and get "success" and "requests" counters along with a "request_latency_ms" stat.
Unsuccessful requests are logged at com.twitter.logging.Level.DEBUG
level.
Further details, including the request and response, are available at
TRACE
level.
The user guide.
com.twitter.finagle.ThriftMux.Client.methodBuilder to construct instances.