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§Additional configuration

There are a number of different types of configuration that you can configure in production. The three mains types are:

Each of these types have different methods to configure them.

§General configuration

Play has a number of configurable settings. You can configure database connection URLs, the application secret, the HTTP port, SSL configuration, and so on.

Most of Play’s configuration is defined in various .conf files, which use the HOCON format. The main configuration file that you’ll use is the application.conf file. You can find this file at conf/application.conf within your project. The application.conf file is loaded from the classpath at runtime (or you can override where it is loaded from). There can only be one application.conf per project.

Other .conf files are loaded too. Libraries define default settings in reference.conf files. These files are stored in the libraries’ JARs—one reference.conf per JAR—and aggregated together at runtime. The reference.conf files provide defaults; they are overridden by any settings defined in the application.conf file.

Play’s configuration can also be defined using system properties and environment variables. This can be handy when settings change between environments; you can use the application.conf for common settings, but use system properties and environment variables to change settings when you run the application in different environments.

System properties override settings in application.conf, and application.conf overrides the default settings in the various reference.conf files.

You can override runtime configuration in several ways. This can be handy when settings vary between environments; you can changing the configuration dynamically for each environment. Here are your choices for runtime configuration:

§Specifying an alternate configuration file

The default is to load the application.conf file from the classpath. You can specify an alternative configuration file if needed:

§Using -Dconfig.resource

This will search for an alternative configuration file in the application classpath (you usually provide these alternative configuration files into your application conf/ directory before packaging). Play will look into conf/ so you don’t have to add conf/.

$ /path/to/bin/<project-name> -Dconfig.resource=prod.conf

§Using -Dconfig.file

You can also specify another local configuration file not packaged into the application artifacts:

$ /path/to/bin/<project-name> -Dconfig.file=/opt/conf/prod.conf

Note that you can always reference the original configuration file in a new prod.conf file using the include directive, such as:

include "application.conf"

§Overriding configuration with system properties

Sometimes you don’t want to specify another complete configuration file, but just override a bunch of specific keys. You can do that by specifying then as Java System properties:

$ /path/to/bin/<project-name> -Dplay.crypto.secret=abcdefghijk -Ddb.default.password=toto

§Specifying the HTTP server address and port using system properties

You can provide both HTTP port and address easily using system properties. The default is to listen on port 9000 at the address (all addresses).

$ /path/to/bin/<project-name> -Dhttp.port=1234 -Dhttp.address=

§Changing the path of RUNNING_PID

It is possible to change the path to the file that contains the process id of the started application. Normally this file is placed in the root directory of your play project, however it is advised that you put it somewhere where it will be automatically cleared on restart, such as /var/run:

$ /path/to/bin/<project-name> -Dpidfile.path=/var/run/

Make sure that the directory exists and that the user that runs the Play application has write permission for it.

Using this file, you can stop your application using the kill command, for example:

$ kill $(cat /var/run/

To prevent Play from creating it’s own PID, you can set the path to /dev/null in your application.conf file:

pidfile.path = "/dev/null"

§Using environment variables

You can also reference environment variables from your application.conf file:

my.key = defaultvalue
my.key = ${?MY_KEY_ENV}

Here, the override field my.key = ${?MY_KEY_ENV} simply vanishes if there’s no value for MY_KEY_ENV, but if you set an environment variable MY_KEY_ENV for example, it would be used.

Because you can reference variables from within other variables, ensure you don’t name your environmental variable the same as the field name.

For example:

MY_TOKEN = foo
MY_TOKEN = ${?MY_TOKEN} # Will reference the previous line, NOT your environmentally set variable

§Server configuration options

Play’s default HTTP server implementation is Netty, and this provides a large number of ways to tune and configure the server, including the size of parser buffers, whether keep alive is used, and so on.

A full list of server configuration options, including defaults, can be seen here:

play.server {

  # The server provider class name
  provider = "play.core.server.NettyServerProvider"

  netty {

    # The number of event loop threads. 0 means let Netty decide, which by default will select 2 times the number of
    # available processors.
    eventLoopThreads = 0

    # The maximum length of the initial line. This effectively restricts the maximum length of a URL that the server will
    # accept, the initial line consists of the method (3-7 characters), the URL, and the HTTP version (8 characters),
    # including typical whitespace, the maximum URL length will be this number - 18.
    maxInitialLineLength = 4096

    # The maximum length of the HTTP headers. The most common effect of this is a restriction in cookie length, including
    # number of cookies and size of cookie values.
    maxHeaderSize = 8192

    # The maximum length of body bytes that Netty will read into memory at a time.
    # This is used in many ways.  Note that this setting has no relation to HTTP chunked transfer encoding - Netty will
    # read "chunks", that is, byte buffers worth of content at a time and pass it to Play, regardless of whether the body
    # is using HTTP chunked transfer encoding.  A single HTTP chunk could span multiple Netty chunks if it exceeds this.
    # A body that is not HTTP chunked will span multiple Netty chunks if it exceeds this or if no content length is
    # specified. This only controls the maximum length of the Netty chunk byte buffers.
    maxChunkSize = 8192

    # Whether the Netty wire should be logged
    log.wire = false

    # The transport to use, either jdk or native.
    # Native socket transport has higher performance and produces less garbage but are only available on linux 
    transport = "jdk"

    # Netty options. Possible keys here are defined by:
    # Options that pertain to the listening server socket are defined at the top level, options for the sockets associated
    # with received client connections are prefixed with child.*
    option {

      # Set the size of the backlog of TCP connections.  The default and exact meaning of this parameter is JDK specific.
      # SO_BACKLOG = 100

      child {
        # Set whether connections should use TCP keep alive
        # SO_KEEPALIVE = false

        # Set whether the TCP no delay flag is set
        # TCP_NODELAY = false



§Logging configuration

Logging can be configured by creating a logback configuration file. This can be used by your application through the following means:

§Bundling a custom logback configuration file with your application

Create an alternative logback config file called logback.xml and copy that to <app>/conf

You can also specify another logback configuration file via a System property. Please note that if the configuration file is not specified then play will use the default logback.xml that comes with play in the production mode. This means that any log level settings in application.conf file will be overridden. As a good practice always specify your logback.xml.

§Using -Dlogger.resource

Specify another logback configuration file to be loaded from the classpath:

$ /path/to/bin/<project-name> -Dlogger.resource=conf/prod-logger.xml

§Using -Dlogger.file

Specify another logback configuration file to be loaded from the file system:

$ /path/to/bin/<project-name> -Dlogger.file=/opt/prod/prod-logger.xml

§Using -Dlogger.url

Specify another logback configuration file to be loaded from an URL:

$ /path/to/bin/<project-name> -Dlogger.url=

§JVM configuration

You can specify any JVM arguments to the application startup script. Otherwise the default JVM settings will be used:

$ /path/to/bin/<project-name> -J-Xms128M -J-Xmx512m -J-server

Next: Setting up a front end HTTP server