static boolean isUsingGemFireDefaultConfig() {
    Configuration configuration = getConfiguration();

    StrSubstitutor strSubstitutor = configuration.getStrSubstitutor();
    StrLookup variableResolver = strSubstitutor.getVariableResolver();

    String value = variableResolver.lookup(GEODE_DEFAULT_PROPERTY);

    return "true".equals(value);
  }
Name of variable that is set to "true" in log4j2.xml to indicate that it is the default geode
config xml.
geode-log4j/src/main/java/org/apache/geode/logging/log4j/internal/impl/Log4jLoggingProvider.java