Logback configuration files are automatically reloaded when scan="true" is set. This is implemented using ReconfigureOnChangeFilter. The actually re-configuration happens in ReconfiguringThread which always creates a new default JoranConfigurator.

This is works as long as the initial JoranConfigurator hasn't been extended to support additional substitution properties.

// create our customized configurator
final JoranConfigurator configurator = new JoranConfigurator() {
   @Override
   protected void addImplicitRules(final Interpreter interpreter) {
      super.addImplicitRules(interpreter);
      // set some properties for log file substitution
      if (null != instanceLogfileDirectory) {
         interpreter.getInterpretationContext().addSubstitutionProperty("my.property", calculateMyPropertyValue());
      }
   }
};

It should somehow be possible to inherit the custom substitution properties into the new JoranConfigurator. Otherwise they are lost on re-configuration.