code: public FileAppender<ILoggingEvent> configureGlobalFileLog(Props props, RootLoggerConfig config, String logPattern) {
      LoggerContext ctx = getRootContext();
      Logger rootLogger = ctx.getLogger(ROOT_LOGGER_NAME);
      FileAppender<ILoggingEvent> fileAppender = newFileAppender(ctx, props, config, logPattern);
      rootLogger.addAppender(fileAppender);
      return fileAppender;
    }
docs: Make logback configuration for a process to push all its logs to a log file.
  <p>
  <ul>
  <li>the file's name will use the prefix defined in {@link RootLoggerConfig#getProcessId()#getLogFilenamePrefix()}.</li>
  <li>the file will follow the rotation policy defined in property {@link #ROLLING_POLICY_PROPERTY} and
  the max number of files defined in property {@link #MAX_FILES_PROPERTY}</li>
  <li>the logs will follow the specified log pattern</li>
  </ul>
  </p>
  
  @see #buildLogPattern(RootLoggerConfig)