<Appenders>
	<Firehose name="firehose">
    	<PatternLayout pattern="%m%n" />
		<DeliveryStreamName>YourFirehoseName</DeliveryStreamName>
        <!-- optional, defaults to ap-northeast-1 -->
		<Region>ap-northeast-1</Region>
        <!-- optional, defaults to UTF-8 -->
        <Encoding>UTF-8</Encoding>
        <!-- optional, defaults to 3 -->
        <MaxRetries>3</MaxRetries>
        <!-- optional, buffer size(KB), 5 ~ 1000, defaults to 1000 -->
        <BufferSize>1000</BufferSize>
        <!-- optional, max delay time(Min.), between every firehose-put calls, 1 ~ 60, defaults to 5 -->
        <MaxPutRecordDelay>5</MaxPutRecordDelay>
	</Firehose>
</Appenders>

• Messages from Logger will be buffered first, the appender makes a put request to Firehose only BufferSize or MaxPutRecordDelay is reached.
• The maximum size of a record sent to Firehose is 1000 KB, if a single one message from Logger exceeds 1000 KB will be discarded. Not implementing an oversize message split to multiple records because I hope a message will not be dismantled when firehose write to S3.
• You may add the log4j-web module in web projects, see [https://logging.apache.org/log4j/2.x/manual/webapp.html]
• If projects use log4j 1.2, you need Log4j 1.2 Bridge, see [https://logging.apache.org/log4j/2.x/log4j-1.2-api/index.html]
• AWS-SDK runs com.amazonaws.http.IdleConnectionReaper in background, it doesn't shutdown automatically. Following code represents how a web project shutdown IdleConnectionReaper without add AWS-SDK jar to your deployment:

@WebListener
public class CleanUpListener implements ServletContextListener {
    @Override
    public void contextDestroyed(final ServletContextEvent sce) {
        try {
            Class.forName("com.amazonaws.http.IdleConnectionReaper").getMethod("shutdown").invoke(null);
        } catch (final Exception e) {}
        
        // or if you import AWS-SDK already, simply call
        // com.amazonaws.http.IdleConnectionReaper.shutdown();
    }
    ...
}

Just remove @WebListener annotation from above code and add a listener element to web.xml

<listener>
        <listener-class>CleanUpListener</listener-class>
</listener>