pekko/akka-docs/general/configuration.rst

.. _configuration:

Configuration
=============

.. sidebar:: Contents

   .. contents:: :local:


Specifying the configuration file
---------------------------------

If you don't specify a configuration file then Akka uses default values, corresponding to the reference 
configuration files that you see below. You can specify your own configuration file to override any 
property in the reference config. You only have to define the properties that differ from the default 
configuration.

By default the ``ConfigFactory.load`` method is used, which will load all ``application.conf`` (and 
``application.json`` and ``application.properties``) from the root of the classpath, if they exists.
It uses ``ConfigFactory.defaultOverrides``, i.e. system properties, before falling back to 
application and reference configuration.

Note that *all* ``application.{conf,json,properties}`` classpath resources, from all directories and
jar files, are loaded and merged. Therefore it is a good practice to define separate sub-trees in the 
configuration for each actor system, and grab the specific configuration when instantiating the ActorSystem.

::
  
  myapp1 {  
    akka.loglevel = WARNING
  }
  myapp2 {  
    akka.loglevel = ERROR
  }

.. code-block:: scala

  val app1 = ActorSystem("MyApp1", ConfigFactory.load.getConfig("myapp1"))
  val app2 = ActorSystem("MyApp2", ConfigFactory.load.getConfig("myapp2"))

If the system properties ``config.resource``, ``config.file``, or ``config.url`` are set, then the
classpath resource, file, or URL specified in those properties will be used rather than the default
``application.{conf,json,properties}`` classpath resources. Note that classpath resource names start
with ``/``. ``-Dconfig.resource=/dev.conf`` will load the ``dev.conf`` from the root of the classpath.

You may also specify and parse the configuration programmatically in other ways when instantiating 
the ``ActorSystem``.

.. includecode:: code/akka/docs/config/ConfigDocSpec.scala
   :include: imports,custom-config

The ``ConfigFactory`` provides several methods to parse the configuration from various sources.

Defining the configuration file
-------------------------------

Each Akka module has a reference configuration file with the default values.

*akka-actor:*

.. literalinclude:: ../../akka-actor/src/main/resources/reference.conf
   :language: none

*akka-remote:*

.. literalinclude:: ../../akka-remote/src/main/resources/reference.conf
   :language: none
   
*akka-testkit:*

.. literalinclude:: ../../akka-testkit/src/main/resources/reference.conf
   :language: none

*akka-beanstalk-mailbox:*

.. literalinclude:: ../../akka-durable-mailboxes/akka-beanstalk-mailbox/src/main/resources/reference.conf
   :language: none

*akka-file-mailbox:*

.. literalinclude:: ../../akka-durable-mailboxes/akka-file-mailbox/src/main/resources/reference.conf
   :language: none

*akka-mongo-mailbox:*

.. literalinclude:: ../../akka-durable-mailboxes/akka-mongo-mailbox/src/main/resources/reference.conf
   :language: none

*akka-redis-mailbox:*

.. literalinclude:: ../../akka-durable-mailboxes/akka-redis-mailbox/src/main/resources/reference.conf
   :language: none

*akka-zookeeper-mailbox:*

.. literalinclude:: ../../akka-durable-mailboxes/akka-zookeeper-mailbox/src/main/resources/reference.conf
   :language: none

A custom ``application.conf`` might look like this::

  # In this file you can override any option defined in the reference files.
  # Copy in parts of the reference files and modify as you please.

  akka {
    event-handlers = ["akka.event.slf4j.Slf4jEventHandler"]
    loglevel        = DEBUG  # Options: ERROR, WARNING, INFO, DEBUG
                             # this level is used by the configured loggers (see "event-handlers") as soon
                             # as they have been started; before that, see "stdout-loglevel"
    stdout-loglevel = DEBUG  # Loglevel for the very basic logger activated during AkkaApplication startup

    # Comma separated list of the enabled modules.
    enabled-modules = ["camel", "remote"]

    # These boot classes are loaded (and created) automatically when the Akka Microkernel boots up
    #     Can be used to bootstrap your application(s)
    #     Should be the FQN (Fully Qualified Name) of the boot class which needs to have a default constructor
    boot = ["sample.camel.Boot",
            "sample.myservice.Boot"]

    actor {
      default-dispatcher {
        throughput = 10  # Throughput for default Dispatcher, set to 1 for as fair as possible
      }
    }

    remote {
      server {
        port = 2562    # The port clients should connect to. Default is 2552 (AKKA)
      }
    }
  }


Config file format
------------------

The configuration file syntax is described in the `HOCON <https://github.com/havocp/config/blob/master/HOCON.md>`_
specification. Note that it supports three formats; conf, json, and properties. 


Including files
---------------

Sometimes it can be useful to include another configuration file, for example if you have one ``application.conf`` with all
environment independent settings and then override some settings for specific environments.

Specifying system property with ``-Dconfig.resource=/dev.conf`` will load the ``dev.conf`` file, which includes the ``application.conf``  

dev.conf:

::

  include "application"

  akka {
    loglevel = "DEBUG"
  }

More advanced include and substitution mechanisms are explained in the `HOCON <https://github.com/havocp/config/blob/master/HOCON.md>`_
specification.


.. _-Dakka.logConfigOnStart:

Logging of Configuration
------------------------

If the system or config property ``akka.logConfigOnStart`` is set to ``on``, then the 
complete configuration at INFO level when the actor system is started. This is useful 
when you are uncertain of what configuration is used.