Configuring Kamon

Kamon uses the Typesafe Config library to manage all that can be configured inside Kamon, as many projects in the JVM world are doing already. This library brings clear and predictable practices for defining application and library settings that can be easily understood and extended. If you are already familiar with this library, you can just jump into the next section.

The Typesafe Config’s standard behavior is very straightforward and we will resume it for you: When you create a configuration object using ConfigFactory.load(), it will read the available configurations from a few predefined places and have them ready for you, so that whenever you want to read a configuration setting they will be looked up in the following order:

  • JVM System Properties.
  • All application.conf files in your classpath.
  • All application.json files in your classpath.
  • All files in your classpath.
  • All reference.conf files in your classpath.

Normally, each library that uses the Typesafe Config library for configuration purposes will ship with a reference.conf file containing sensible default values for all the settings that can be configured and the user will provide “overrides” to those values primarily via your own application.conf file or via system properties. Probably an image of the common lookup priorities will settle quickly in your mind:

These configuration files are usually written using the HOCON notation. All Kamon modules that need configuration ship with a reference.conf file where default settings are contained and you are free to override any of those values by supplying your owns in your application.conf file. Whenever we refer to a configuration setting throughout the docs, we are certainly referring to a setting available in a module’s reference.conf file that you can override at your wish.

This resume is just a very high level overview of what the Typesafe Config library can do for you, please refer to their documentation to learn how to slice and dice with configuration settings and make the best possible profit out of it.

Providing a Custom Config Object

If you need to prevent Kamon from using the standard behavior of calling ConfigFactory.load(), there is an additional overload of the Kamon.start(..) method that accepts a configuration object to be used instead. This is how you would provide such a custom configuration object:

object CustomConfiguration {
  val customConfig = ConfigFactory.load("custom-config")
  val codeConfig = ConfigFactory.parseString(
    "kamon.metric.track-unmatched-entities = no")

  // Kamon gets initialized with the provided configuration rather
  // than calling ConfigFactory.load() itself.

  // This application wont terminate unless you shutdown Kamon.
public class CustomConfiguration {
  public static void main(String[] args) {
    final Config customConfig = ConfigFactory.load("custom-config");
    final Config codeConfig = ConfigFactory.parseString(
      "kamon.metric.track-unmatched-entities = no");

    // Kamon gets initialized with the provided configuration rather
    // than calling ConfigFactory.load() itself.

    // This application wont terminate unless you shutdown Kamon.

Please note that when you provide your own Config object, Kamon will use that and only that object as a configuration settings source. You must ensure that the Config object you are supplying contains both your custom settings and all the reference settings available in the classpath. Most APIs in the typesafe-config’s ConfigFactory class already take care of that but if that isn’t the case for you then simply adding a .withFallback(ConfigFactory.defaultReference()) to your configuration object you can ensure that everything Kamon needs is in place.

Special Considerations for Akka and Spray

Kamon core components use Akka internally for several purposes and some modules make use of Spray as well, but all of this happens in a internal actor system created by Kamon for it’s own usage. If your application is using Akka or Spray, you probably don’t want all the settings applied to your application’s actor system to be applied to Kamon’s actor system as well, that’s why we have a special treatment of configuration settings for the akka.* and spray.* patterns.

When Kamon’s internal actor system is created we strip away all the akka.* and spray.* configuration settings available (either from standard behavior or from a provided Config object) and we add all the configuration settings available under the kamon.internal-config to the resulting Config object before supplying it to the internal actor system. By doing this, any customizations you do to Akka or Spray for your application wont affect Kamon’s behavior, but still you can provide custom settings for Kamon’s internal actor system if you want to.

For example, if you wish to change the log level and the parallelism factor for the default dispatcher in Kamon’s internal actor system, you would need to provide something like this in your configuration file:

kamon.internal-config {
  akka {
    loglevel = DEBUG

    actor.default-dispatcher {
      fork-join-executor.parallelism-factor = 1.0