How can I configure system properties or logback configuration variables from typesafe config?

Question

I have variables with defaults in my logback.xml configuration file, and I would like to be able to optionally set these variables from my typesafe config app

Answer 1

I chose to programmatically configure logback having typesafe config. It turned out to be easy.

def enableRemoteLogging(config: Config) = {
    val ctx = LoggerFactory.getILoggerFactory.asInstanceOf[LoggerContext]

    val gelf = new GelfAppender
    gelf.setGraylog2ServerHost(config.getString("logging.remote.server"))
    gelf.setUseLoggerName(true)
    gelf.setUseThreadName(true)
    gelf.setUseMarker(true)
    gelf.setIncludeFullMDC(true)
    gelf.setContext(ctx)
    gelf.start()

    LoggerFactory.getLogger(Logger.ROOT_LOGGER_NAME)
      .asInstanceOf[ch.qos.logback.classic.Logger]
      .addAppender(gelf)
  }

Answer 2

I'm not familiar with Logback, but a normal Akka application ships with default settings in its reference.conf, and you override these settings in an application.conf. It sounds like you want to add a third layer of configuration, which is certainly your right!

The easiest way I can see is to change your application.conf to include your foo.conf rather than the other way around. That way Akka will load the application.conf, which will then load foo.conf.

But that may not work if you need a differently-named conf file for each JAR distribution. In which case I recommend you look into Merging Config Trees to programmatically load and combine configuration. Actually, Reading configuration from a custom location in the Akka Configuration docs is almost exactly what you want, except you will want to load myConfig from a classpath resource rather than by parsing a string (see the Typesafe Config docs to find out how to do that).

Regarding the Logback configuration, like I said, I don't know Logback. But you can read values out an Typesafe configuration like so, and you can set the Logback root logger level like so.

Answer 3

You can use the PropertyDefiner interface that logback provides. Non trivial scaffolding but allows you to configure using XML instead of within your application. E.g.:

package com.myapp;

import ch.qos.logback.core.PropertyDefinerBase;
import com.typesafe.config.ConfigFactory;

public class TypesafeConfigPropertyDefiner extends PropertyDefinerBase {

    private String propertyName;

    @Override
    public String getPropertyValue() {
        return ConfigFactory.load().getString( propertyName );
    }

    public void setPropertyName( String propertyName ) {
        this.propertyName = propertyName;
    }
}

Then, in your logback.xml file:

<configuration>
    <define name="loglevel" class="com.myapp.TypesafeConfigPropertyDefiner">
        <propertyName>myapp.logging.loglevel</propertyName>
    </define>
    <root level="${loglevel}">
       ...
    </root>
</configuration>

Now, the above logback.xml file will read myapp.logging.loglevel from your typesafe config file (e.g. application.conf).