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§Configuring the Akka HTTP server backend

By default, Play uses the Akka HTTP server backend.

Like the rest of Play, the Akka HTTP server backend is configured with Typesafe Config.

# Copyright (C) Lightbend Inc. <https://www.lightbend.com>

# Configuration for Play's AkkaHttpServer
play {

  server {
    # The server provider class name
    provider = "play.core.server.AkkaHttpServerProvider"

    akka {
      # How long to wait when binding to the listening socket
      bindTimeout = 5 seconds

      # How long a request takes until it times out. Set to null or "infinite" to disable the timeout.
      requestTimeout = infinite

      # Enables/disables automatic handling of HEAD requests.
      # If this setting is enabled the server dispatches HEAD requests as GET
      # requests to the application and automatically strips off all message
      # bodies from outgoing responses.
      # Note that, even when this setting is off the server will never send
      # out message bodies on responses to HEAD requests.
      transparent-head-requests = off

      # If this setting is empty the server only accepts requests that carry a
      # non-empty `Host` header. Otherwise it responds with `400 Bad Request`.
      # Set to a non-empty value to be used in lieu of a missing or empty `Host`
      # header to make the server accept such requests.
      # Note that the server will never accept HTTP/1.1 request without a `Host`
      # header, i.e. this setting only affects HTTP/1.1 requests with an empty
      # `Host` header as well as HTTP/1.0 requests.
      # Examples: `www.spray.io` or `example.com:8080`
      default-host-header = ""

      # The default value of the `Server` header to produce if no
      # explicit `Server`-header was included in a response.
      # If this value is null and no header was included in
      # the request, no `Server` header will be rendered at all.
      server-header = null
      server-header = ${?play.server.server-header}

      # Configures the processing mode when encountering illegal characters in
      # header value of response.
      #
      # Supported mode:
      # `error`  : default mode, throw an ParsingException and terminate the processing
      # `warn`   : ignore the illegal characters in response header value and log a warning message
      # `ignore` : just ignore the illegal characters in response header value
      illegal-response-header-value-processing-mode = warn

      # This setting is set in `akka.http.server.parsing.max-content-length`
      # Play uses the concept of a `BodyParser` to enforce this limit, so we override it to infinite.
      max-content-length = infinite

      # This setting is set in `akka.http.server.parsing.max-header-value-length`
      # and it limits the length of HTTP header values.
      max-header-value-length = 8k


      # Enables/disables inclusion of an Tls-Session-Info header in parsed
      # messages over Tls transports (i.e., HttpRequest on server side and
      # HttpResponse on client side).
      #
      # See Akka HTTP `akka.http.server.parsing.tls-session-info-header` for
      # more information about how this works.
      tls-session-info-header = on

    }
  }

}

The configurations above are specific to Akka HTTP server backend, but other more generic configurations are also available:

# Copyright (C) Lightbend Inc. <https://www.lightbend.com>

play {

  server {

    # The root directory for the Play server instance. This value can
    # be set by providing a path as the first argument to the Play server
    # launcher script. See `ServerConfig.loadConfiguration`.
    dir = ${?user.dir}

    # HTTP configuration
    http {
      # The HTTP port of the server. Use a value of "disabled" if the server
      # shouldn't bind an HTTP port.
      port = 9000
      port = ${?PLAY_HTTP_PORT}
      port = ${?http.port}

      # The interface address to bind to.
      address = "0.0.0.0"
      address = ${?PLAY_HTTP_ADDRESS}
      address = ${?http.address}

      # The idle timeout for an open connection after which it will be closed
      # Set to null or "infinite" to disable the timeout, but notice that this
      # is not encouraged since timeout are important mechanisms to protect your
      # servers from malicious attacks or programming mistakes.
      idleTimeout = 75 seconds
    }

    # HTTPS configuration
    https {

      # The HTTPS port of the server.
      port = ${?PLAY_HTTPS_PORT}
      port = ${?https.port}

      # The interface address to bind to
      address = "0.0.0.0"
      address = ${?PLAY_HTTPS_ADDRESS}
      address = ${?https.address}

      # The idle timeout for an open connection after which it will be closed
      # Set to null or "infinite" to disable the timeout, but notice that this
      # is not encouraged since timeout are important mechanisms to protect your
      # servers from malicious attacks or programming mistakes.
      idleTimeout = ${play.server.http.idleTimeout}

      # The SSL engine provider
      engineProvider = "play.core.server.ssl.DefaultSSLEngineProvider"
      engineProvider = ${?play.http.sslengineprovider}

      # HTTPS keystore configuration, used by the default SSL engine provider
      keyStore {
        # The path to the keystore
        path = ${?https.keyStore}

        # The type of the keystore
        type = "JKS"
        type = ${?https.keyStoreType}

        # The password for the keystore
        password = ""
        password = ${?https.keyStorePassword}

        # The algorithm to use. If not set, uses the platform default algorithm.
        algorithm = ${?https.keyStoreAlgorithm}
      }

      # HTTPS truststore configuration
      trustStore {

        # If true, does not do CA verification on client side certificates
        noCaVerification = false
      }

      # Whether JSSE want client auth mode should be used. This means, the server
      # will request a client certificate, but won't fail if one isn't provided.
      wantClientAuth = false

      # Whether JSSE need client auth mode should be used. This means, the server
      # will request a client certificate, and will fail and terminate the session
      # if one isn't provided.
      needClientAuth = false
    }

    # The path to the process id file created by the server when it runs.
    # If set to "/dev/null" then no pid file will be created.
    pidfile.path = ${play.server.dir}/RUNNING_PID
    pidfile.path = ${?pidfile.path}

    websocket {
      # Maximum allowable frame payload length. Setting this value to your application's
      # requirement may reduce denial of service attacks using long data frames.
      frame.maxLength = 64k
      frame.maxLength = ${?websocket.frame.maxLength}
    }

    debug {
      # If set to true this will attach an attribute to each request containing debug information. If the application
      # fails to load (e.g. due to a compile issue in dev mode), then this configuration value is ignored and the debug
      # information is always attached.
      #
      # Note: This configuration option is not part of Play's public API and is subject to change without the usual
      # deprecation cycle.
      addDebugInfoToRequests = false
    }
  }

  editor = ${?PLAY_EDITOR}

}

You can read more about the configuration settings in the Akka HTTP documentation.

Note: Akka HTTP has a number of timeouts configurations that you can use to protect your application from attacks or programming mistakes. The Akka HTTP Server in Play will automatically recognize all these Akka configurations. For example, if you have idle-timeout and request-timeout configurations like below:

akka.http.server.idle-timeout = 20s
akka.http.server.request-timeout = 30s

They will be automatically recognized. Keep in mind that Play configurations listed above will override the Akka ones.

There is also a separate configuration file for the HTTP/2 support in Akka HTTP, if you have enabled the `AkkaHttp2Support` plugin:

# Copyright (C) Lightbend Inc. <https://www.lightbend.com>

# Determines whether HTTP2 is enabled.
play.server.akka.http2 {
  enabled = true
  enabled = ${?http2.enabled}
  alwaysForInsecure = false  # @ApiMayChange
  alwaysForInsecure = ${?http2.alwaysForInsecure}
}

Note: In dev mode, when you use the run command, your application.conf settings will not be picked up by the server. This is because in dev mode the server starts before the application classpath is available. There are several other options you’ll need to use instead.

§Direct Akka HTTP configuration

If you need direct access to Akka HTTP’s ServerSettings and ParserSettings objects you can do this by extending Play’s AkkaHttpServer class with your own. The AkkaHttpServer class has several protected methods which can be overridden to change how Play configures its Akka HTTP backend.

Note that writing your own server class is advanced usage. Usually you can do all the configuration you need through normal configuration settings.

The code below shows an example of a custom server which modifies some Akka HTTP settings. Below the server class is a ServerProvider class which acts as a factory for the custom server.

package server

import java.util.Random
import play.core.server.AkkaHttpServer
import play.core.server.AkkaHttpServerProvider
import play.core.server.ServerProvider
import akka.http.scaladsl.ConnectionContext
import akka.http.scaladsl.model.HttpMethod
import akka.http.scaladsl.settings.ParserSettings
import akka.http.scaladsl.settings.ServerSettings

/** A custom Akka HTTP server with advanced configuration. */
class CustomAkkaHttpServer(context: AkkaHttpServer.Context) extends AkkaHttpServer(context) {
  protected override def createParserSettings(): ParserSettings = {
    val defaultSettings: ParserSettings =
      super.createParserSettings()
    defaultSettings.withCustomMethods(HttpMethod.custom("TICKLE"))
  }
  protected override def createServerSettings(
      port: Int,
      connectionContext: ConnectionContext,
      secure: Boolean
  ): ServerSettings = {
    val defaultSettings: ServerSettings =
      super.createServerSettings(port, connectionContext, secure)
    defaultSettings.withWebsocketRandomFactory(() => new Random())
  }
}

/** A factory that instantiates a CustomAkkaHttpServer. */
class CustomAkkaHttpServerProvider extends ServerProvider {
  def createServer(context: ServerProvider.Context) = {
    val serverContext = AkkaHttpServer.Context.fromServerProviderContext(context)
    new CustomAkkaHttpServer(serverContext)
  }
}

Once you’ve written a custom server and ServerProvider class you’ll need to tell Play about them by setting the play.server.provider configuration option to the full name of your ServerProvider class.

For example, adding the following settings to your build.sbt and application.conf will tell Play to use your new server for both the sbt run task and when your application is deployed.

build.sbt:

PlayKeys.devSettings += "play.server.provider" -> "server.CustomAkkaHttpServerProvider"

application.conf:

play.server.provider = server.CustomAkkaHttpServerProvider

Next: Configuring Netty Server Backend

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