HTTP Server Warmup

There may be occasions where we want to exercise specific code paths before accepting traffic to the server (e.g., for triggering JIT in the JVM). We can do this via server warmup.

Warmup

Finatra provides a warmup lifecycle callback function which will be executed in the correct phase of server startup, i.e, before the server’s external HTTP port(s) are bound and thus before the TwitterServer Lifecycle Management /health endpoint responds with OK.

See here for more information on the lifecycle of a Finatra server.

To perform warmup, simply override this callback method and implement your logic. E.g.,

import DoEverythingModule
import ExampleController
import ExampleFilter
import ExampleWarmupHandler
import MalformedURLExceptionMapper
import com.twitter.finatra.http.HttpServer
import com.twitter.finatra.http.filters.{CommonFilters, LoggingMDCFilter, TraceIdMDCFilter}
import com.twitter.finatra.http.routing.HttpRouter

object ExampleServerMain extends ExampleServer

class ExampleServer extends HttpServer {

  override val modules = Seq(
    DoEverythingModule)

  override def configureHttp(router: HttpRouter): Unit = {
    router
      .filter[LoggingMDCFilter[Request, Response]]
      .filter[TraceIdMDCFilter[Request, Response]]
      .filter[CommonFilters]
      .add[ExampleFilter, ExampleController]
      .exceptionMapper[MalformedURLExceptionMapper]
  }

  override protected def warmup(): Unit = {
    // YOUR WARMUP LOGIC HERE <----------------------------------------------
  }

c.t.finatra.http.routing.HttpWarmup

Finatra provides a utility, c.t.finatra.http.routing.HttpWarmup which will route requests to correct service implementation configured by the HttpRouter.

The most common way to use the c.t.finatra.http.routing.HttpWarmup is via a constructor-arg to an implementation of a c.t.inject.utils.Handler.

The Finatra c.t.inject.serverTwitterServer provides a #handle[T <: Handler: Manifest] utility which simply instantiates a given c.t.inject.utils.Handler via the injector and invokes its #handle() function.

Combining the above, if we wanted to run an initial call through our HTTP service we could create the following handler:

import com.twitter.finatra.http.routing.HttpWarmup
import com.twitter.finatra.httpclient.RequestBuilder._
import com.twitter.inject.utils.Handler
import javax.inject.Inject

class ExampleWarmupHandler @Inject()(
  warmup: HttpWarmup)
  extends Handler {

  override def handle(): Unit = {
    try {
      warmup.send(
        get("/ping"))
    } catch {
      case e: Throwable =>
        // Here we don't want a warmup failure to prevent server start-up --
        // this is important if your service will call downstream services
        // during warmup that could be temporarily down or unavailable.
        // We don't want that unavailability to cause our server to fail
        // warm-up and thus prevent the server from starting. So we simply
        // log the error message here.
        error(e.getMessage, e)
    }
    info("Warm-up done.")
  }
}

The handler above simply tries to hit the /ping endpoint of the server.

Warning

As noted above, be careful about exceptions which occur from calling endpoints on your service during warmup. Exceptions which escape the handler will potentially stop your server from starting and thus, you most likely do not want an exception from a warmup call to propagate out of the handler.

You would then run this handler in the warmup() lifecycle callback. E.g.,

import DoEverythingModule
import ExampleController
import ExampleFilter
import ExampleWarmupHandler
import MalformedURLExceptionMapper
import com.twitter.finatra.http.HttpServer
import com.twitter.finatra.http.filters.{CommonFilters, LoggingMDCFilter, TraceIdMDCFilter}
import com.twitter.finatra.http.routing.HttpRouter

object ExampleServerMain extends ExampleServer

class ExampleServer extends HttpServer {

  override val modules = Seq(
    DoEverythingModule)

  override def configureHttp(router: HttpRouter): Unit = {
    router
      .filter[LoggingMDCFilter[Request, Response]]
      .filter[TraceIdMDCFilter[Request, Response]]
      .filter[CommonFilters]
      .add[ExampleFilter, ExampleController]
      .exceptionMapper[MalformedURLExceptionMapper]
  }

  override protected def warmup(): Unit = {
    handle[ExampleWarmupHandler]() <----------------------------------------------
  }
}

More information

For more information, we encourage you to take a look at the full finatra/examples in the github source.