===========
Logging
===========

=> The process of storing application execution details into a file is called as Logging.

=> Log messages will help us in understanding run-time behaviour of the application.

=> Using log messages we can find root cause of the exception in the code.

=====================
Logging Architecture
=====================

1) Logger

2) Layout

3) Appender

=> Logger is a class which is providing methods to generate log messages.

2) Layout represents log message structure.

3) Appender represents destination to store log messages.

	Ex: ConsoleAppender, FileAppender
	
=====================
Logging Frameworks
=====================

1) Log4J
2) Log4J2
3) Logback
4) Logstash

Note: In SpringBoot we will get "logback" by default.

================
What is SLF4J ?
================

=> Simple logging facade for Java

=> IT is an API that supports several logging frameworks available in the market.

=> If we use SLF4J in project then can we can configure any logging framework at the time of deployment.

============
Log Levels
============

=> We have several log levels

	TRACE > DEBUG -> INFO > WARN > ERROR
	
=> When we set one log level from that level all higher level log methods will be executed.

Note : In SpringBoot the default log level is INFO.	We can change that in application.properties file 

		logging.level.root=DEBUG
		logging.file.name=app.log
	
=> For every log level, Logger class provided method to generate log msg.

Note: Logger class methods we can use like below.


@Service
@Slf4j
public class UserService {

	// private Logger log = LoggerFactory.getLogger(UserService.class);

	public void saveUser() {
		log.trace("This is trace msg");
		log.debug("This is debug msg");
		log.info("This is info msg");
		log.warn("This is warn msg");
		log.error("This is error msg");
	}

}

@Service
@Slf4j
public class ReportService {

	public void generateReport() {
		log.info("method started");
		try {
			int i = 10 / 0;
		} catch (Exception e) {
			// e.printStackTrace();
			log.error(e.getMessage());
		}
		log.info("method ended");
	}
}
==================================================

====================
RollingFileAppender
====================

1) Time based rolling

2) Size based rolling  


=> Time based rolling means every day new log file will be created with timestamp.

=> Size based rolling means after given limit reached then new log file will be created.

=========================
What is logback.xml ?
=========================

=> logback.xml is used to customize logging in our application.

=> In logback.xml we will configure below components

	1) Rolling File Appender with policy

	2) Log Msg Pattern

	3) Log Level

=> We will keep logback.xml under "src/main/resources" folder	

-------------------- logback.xml --------------------------------

<configuration>

	<appender name="RollingFile"
		class="ch.qos.logback.core.rolling.RollingFileAppender">
		<file>ashokit.log</file>
		<encoder>
			<pattern>%d [%thread] %-5level %-50logger{40} - %msg%n</pattern>
		</encoder>
		<rollingPolicy
			class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">
			<fileNamePattern>ashokit-%d{yyyy-MM-dd}.%i.log</fileNamePattern>
			<maxFileSize>1GB</maxFileSize>
			<maxHistory>30</maxHistory>		
		</rollingPolicy>
	</appender>	
	<root level="INFO">
		<appender-ref ref="RollingFile" />
	</root>
	
</configuration>

------------------------------------------------------------

================
Log Monitoring
================

=> The process of getting log msgs from log file is called as Log Monitoring.

=> To monitor log msgs we can use several tools 

		a) Putty
		b) MobaXterm
		c) WinScp
		d) ELK / EFK  (Free)
		e) Splunk (Commercial)		
		

=> Putty, MobaXterm and WinScp tools are used to connect from windows to linux machines.

=> ELK and Splunk tools will provide user interface to monitor logs of our application.


============
Assignment
============

=> Setup ELK stack in windows machine to monitor logs of our springboot application.

@@ Reference Video : https://youtu.be/n2HHAvpn6Jo?si=wcK0VTo71OBC96o_



=========
Summary
=========

1) What is Logging

2) Why Logging

3) Logging Architecture

4) Log Levels

5) Logging in SpringBoot

6) Rolling Policies

7) SL4J Vs Log4J

8) Log Monitoring

		- Putty
		- WinScp
		- ELK
		- SPlunk