MAC

Installation

• Homebrew
• brew install putty
• MacPorts
• port install putty
•  

Putty

• puttygen privatekey.ppk -O private-openssh -o privatekey.pem

Linux

Unix vs Linux

• Unix developed in mid-1970 for multi-user, multi-tasking
• Mostly used by SUN and their operating system is Solaris, HP-UX, AIX 
• Supports fewer file systems
  
• Linux in 1991 by Linus Torvalds
• Linux is mostly free
• Open source
• Used mostly by Developer communities, or companies(REDhad, Centos, Debian and many)
• Can be installed on variety of computer hardware, mobiles, tablets, video games, super computers, main frames
• Can be installed on any hardware that is running by Intel & AMD processor

Oracle Virtual Box

1. Free and Open source Hypervisor for x86 computers developed by Oracle
   

Different Linux distributions

• 200+ OS derived from linux like.. Redhat, Ubuntu, Fedora, suse, Debian, Cent os, 
  

• Client
• Windows
• Cygwin 
• mac/Linux client
  
• ssh -V
• Client Server architechture
• ssh client on client system & ssh daemon on Server
• commands
• (sudo) yum -y install nano
• nano /etc/ssh/sshd_config
• edit line #PermitRootLogin yes to no
  
• systemctl restart sshd
• Navigation commands
• ~   short cut for home directory
• write file
• echo > a.txt
• touch b.txt   to create empty file
  
• running as admin
  
• sudo <command>   run single command as administrator
  
• sudo su    to become administrator
• Install new package
• yum install java        yum is package manager for Centos systems
  
• java -version
• Bash & Shell
• Shell is a processor to process what ever we type in terminal(bash, ksh, fish..)
• Bash is a default processor
• Bash script
• #!/bin/bash                -> so say use bash shell
  for i in 1 2 3 4 5; do
  echo "Hello $i";
  sleep 2;
  done;
• bash <script name>
• Background process
• & at the end of command
• stopping background process
• ps aux
• kill -9 <pid>
• start HTTP server
• sudo python -m SimpleHTTPServer 80
• Environment Variables
• env    to list all env variables
• echo $PATH
• export  - adds new environment variable
•  export abc="asdfasdf"
  
• Strings
• "   -> interpolating variables
  
• '   -> preserving strings exactly
  
• `  -> interpolating command output
• echo "today is `date`"
• Linux commands demistified
• linux commands are executables
• which <command> gives the location

SSH Fundamentals

• Interactive ssh
• ssh user@[hostname/ipaddress]
• long lived processes
• start process and keep it running after terminating ssh session
  
• nohup <command>
• It separates process from terminatl
• non-interactive ssh
• run multiple commands at a time
• ssh user@[hostname/ipaddress]  <command>

Creating Server Alias

• ~/.ssh/config add following
  Host [server_nickname]
  hostname [Server IP address]
  user [username]

How SSH works

• SSH daemon listens at port 22
• ECDSA is unique signature of server which can't be tampered. ESDSA is sent to client
• Encrypted communication channel gets created between both parties
• Client sends authentication details on encrypted channel
• Server verified 
• communication channel gets established. 

Uploading files(SCP)- uses ssh internally

• upload
• scp [local source path] user@[hostname/ipaddress]:[server_target_path]
•  download
•  
• scp user@[hostname/ipaddress]:[server_source_path]  [local target path] 

SFTP - ssh file transfer protocol

•  download cyberduck

SSH Key Authentication

• Avoid typing password
• More secure
• Problem with passwd authentication
• Secret information is sent over communication channel which can compromise security
• Process
• Generate public and private key (ssh key pair)
• Upload public key on server
• Tell client to use SSH authentication
• Private & Public key
• AssyPublic key can be distributed
• Private key to be kept confidential
• Data encrypted with public key can only be decrypted with private key
• Private key cannot be figured out from public key
• Public key can be figured/derived out from Private key
•  Generate ssh keys
• ssh-keygen -t rsa -b 4086 -C "just comments"
• Connect to server ~/.ssh/authorized_keys file
• copy content of public key to authorized_keys on a new line
• Test ssh keys
• ssh -i [privatekey] [user]@[server]

Amazon EC2

• sudo su -    to become a root user
  
• Dir structure
• /   ->ROOT directory similar to  C:\ in windows
  
• /root -> home directory for root user- similar to C:\Document and Setting\Administrator
  
• /home  -> home directory for other users- similar to C:\Document and Setting\username
• /usr -> softwares are installed- similar to c:\program files
• /bin -> commands used by all users
  
• /sbin -> commands used by super user(root)
  
•  /var -> container variable data like logs, mails..
• Basic commands
• User Management
• Super or root user -> most powerful & admin user
• /root   is home directory with shell /bin/bash
  
• Sytem user ->Created by applications or softwares
• /var/ftp  is home directory with shell /sbin/no login
  
• Normal user ->
• /home/<user> is home directory with shell /bin/bash
• user creation
• useradd <option> <name>
• UID & GID will be assigned to user
• Software Management
• yum for REDHAT
• yum install <package>
• yum remove 
• yum update
• yum info
• yum list
• yum install wget
• Networking
• hostname    ->servername
• init 6   or reboot -> restart system
• ping  -> to check if target is available or not
• wget -> download files/packages
• ifconfig -> to get ipaddress of your system
  
• telnet ->to check if a particular port is used or not
  
• curl ->access appln as from browser
  
• port numbers
• ftp - 21
  
• ssh -22
  
• telnet - 23
  
• smtp - 25
  
• dns - 53
  
• http - 80
  
• https - 443
• ports usage
• netstat -tulpn
• Services(systemctl)
• Service
• Controls starting and stopping of services
• service <name> <status | start | stop | reload | restart>
• yum install httpd   -> command to install http
  • service httpd status
  • service httpd start
  • telnet localhost 80
  • curl localhost
• chkconfig
• Check availability of service
• chkconfig --list
• chkconfig <service> <on | off> -> to make service available/unavailable after restart(boot time)
  

SSH(Secure shell)

• Method for secure remote login from one computer to another. 
• Provides alternative options for authentication
• Protects communications security and integrity with strong encryption
• port - 22
• Daemon - sshd
• conf file - /etc/ssh/sshd_config
•  HTTP
  
  • port - 80
  • Daemon - httpd
  • conf file - /etc/httpd/conf/httpd_config
  • default file - /var/www/html 
   

Process Management

• ps -ef  -> list of processes which are running in system
  
• kill -9 -> kill a process or service
• jobs -> gives list of jobs getting executed
  
• fg & %<job id> -> run process in foreground
  
• bg -> run in background
  
• top -> list top 20 process which are consuming more cpu

Archiving

• gzip
• Create compressed file 
• gzip <file>  -> file.gz gets created
  
• gunzip
•  gunzip <file.gz>
  
• tar
• extract tar file
• works on directories
• tar -cvf <directory> dir1.tar directory1
• tar -xvf  dir1.tar   ->  tar is a file
  
• gzip dir1.tar ->dir1.gz
• tar -xvzf dir1.gz  to extrat tar & directories -> does 2 steps

CronTab

• daemon called crond
• job scheduling
• crontab -l
• List crons
  
• crontab -e
• Min  Hr Day_Of_Month Month  Day_of_week  <command>
  
• Execute job at 8.30 in mornring
• 30 8 * * * 
• Execute job at 2 pm every saturday
• 0 14 * * 6
• Execute job at 12am on Jul1st
• 00 00 1 6 *
• Execute job at 3.30pm every month 25th
• 30 15 25 * *

Link files

• Softlink
• shortcut file
• ln -s <source file> <dest file>
• used to create short cut of shell script at /usr/local/bin/hello
  
• Harklink
• Backup file
• ln <source file> <dest file>

Windows to Linux

• Mobaxterm
• winscp

Copy from LINUX to LINUX server

• scp

Spring

• To build enterprise java applications
• simpler & light weight
• Spring 4 Key Features
• Inversion of Control
• Dependency injection
• Spring AOP
• Spring MVC
• Spring 5 new features
• Spring WebFlux

Spring Framework

• Goals
• Light weight java development with pojos
• Dependency injection for loose coupling
• Declarative programming with AOP(Aspect Oriented Programming)
• Minimize boiler plate java code
• Core Container
• Beans
• Core
• SpEL
• Context
• Infrastructure
• AOP
• Aspects
• Instrumentation
• Messaging
• Data access Layer
• JDBC
• ORM -> Object relation mapping
  
• Transactions
• OXM
• JMS
• Web Layer
• Servlet
• Websocket
• web
• portlet
• Test layer
• Unit
• integration
• Mock

Spring Projects

•     Only use what you need
• Spring Cloud, Spring Data
• Spring Batch, Spring Security
• Spring for Android, Spring for web flow
• Spring for Webservices, Spring for LDAP
• Spring Boot, Spring Social

Dev Env setup

• Tomcat8.5 + Eclipse 
• Create Project
• Create a new folder lib in the project
  
• Download spring-framework-5.0.2-Release-dist.zip
• Add jar to the lib folder in the project
  
• Project properties -> java build path -> libraries -> classpath -> add jars -> select jars from lib folder
• Now referenced libraries should show the jars added

Spring Inversion of Control

• Design process of externalizing of construction and management of Objects

Spring Container

• Primary functions 
• Create and manage Objects(Inversion of control) - Object Factory
  
• Inject Objects dependencies (Dependency management) -
  
• Configuration
• XML configuration (legacy)
• Java annotations(modern)
• Java source code(modern)

Spring development process

• Configure spring beans in config file
  
• applicationContext.xml -> define beans with bean ID & fully qualified class name
• Create Spring container
• This is generally known as ApplicationContext
• ClassPathXmlApplicationContext context = new  ClassPathXmlApplicationContext("applicationContext.xml");
• Retrieve beans from container
• Coach coach = context.getBean("myCoach",MyCoach.class);
  

Spring Dependency Injection

• Dependency is same as helper objects
  
• Injection Types
• Constructor Injection
• Setter Injection
• Development process - constructor injection
  
• Create Dependency Interface & class that implements it
• Create Constructor in your class with parameter as Dependency Interface type
• Spring bean container/context
• Define Dendency bean
• Define regular bean and inject Dependency-bean as Constructor-arg
• Development process - setter injection

Bean Scopes

• Singleton
• for stateless beans
  
• prototype
• new object for each request
• for statefull bean
  
• request
•  
• session
• global-session
  

Configuration with Annotations(XML Component scan)

• XML configuration can be too verbose for big projects
• Scanning for component classes
• Spring scans classes for special annotations
• They automatically register them in container
• Development process
• Enable component scanning in spring config file
• provide the base package for  component scan in config file
  
• add @Component annotation to java class
• retrieve bean  from spring container using context.getBean(<beanID>,Bean.class)
  
• autoWiring
• Spring looks for class that matches the property(class/interface) and injects it automatically.
• Injection types
• Construction
• @Autowired on top of constructor
  
• Setter
• Field

Java Configuration

• Development process
• Annotate java class with @ComponentScan & @Configuration

Spring MVC

• webpages to layout UI components
• Spring beans(Controller, services)
  
• Spring configuration(xm, annotations or java)
• Controller
• @Controller which inherits from Component
• @RequestMapping -> controller method
  
• Model
• It is container of application data
• Form Tags

AOP(Aspect Oriented Programming).

• It is module/code for cross cutting concenrs
• Technique based on concept of Aspect
• Aspect encapsulates cross-cutting logic
• It can be reused at multiple locations
• same aspect can be applied based on configuration
• Benefits
• Code lies in one class and not scattered
• code reuse and easy to change
• Business code is clean
• Configurable
• Use cases
• Logging, security, transactions
• audit logging
• exception handling
• API Management
• analytics/metrics
• Disadvantages
• Too many aspects - hard to follow app flow
• minor perf cost for aspect execution
• Terminology
• Aspect - It is module/code for cross cutting concerns
• Advice -What action is taken and when it should be applied
• BeforeAdvice..........
• Joint Point - When to apply code during program execution
  
• Pointcut-
• Weaving 
• Connecting aspects to target objects to create an advised object
• types of weaving
• Compile time, load time or run time
• Frameworks
• SpringAOP, AspectJ
• SpringAOP advantages
  
• Simpler than SpectJ
• users Proxy pattern
• can migrate to AspectJ when using @Aspect annotation
• Spring AOP disadvantages
• supports only method-level joint points
• can apply aspects to beans created by Spring app context
• minor perf impact due to runtime aspect

Spring Security

• HTTP Basic Authentication
• builtin dialog from browser
  
• Default login form
• Spring provides default form
  
• Custom login form

Spring REST

• JSON
• Databinding 
• process of converting json data into java pojo and vice versa
  
• spring uses jackson project behind the scene
• Json data sent to spring controller will be automatically converted to pojo
• java object returned from rest  controller will be converted to JSON
• HTTP Request Message
• Request line
• Header variables
• Message Body
• REST Controller
• Exception Handler
• ResponseEntity is a wrapper on HTTP response object
• 
  

Spring JDBC

• Spring simplifies the way we use java technologies
• JDBC 
• Developers write lot of code which is repeated across classes in application
  Connection, Statement, setParameters,
• handle checked exceptions
  
• SpringJDBC
• Simplifies jdbc by creating JDBCTemplate
• it is combination of JDBC + Template design pattern
• Template carries common or boiler plate code and reduces amount of developers work
  
• JDBCTemplate depends on javax.sql.DataSource
• Steps to use JDBCTemplate
• config.xml
• create/configure bean dataSource for class DriverManagerDataSource providing driverClassName, url, user, pwd
  
• create/configure bean jdbcTemplate for class JDBCTemplate passing dataSource from above step
  
• jdbcTemplat.update(sql, <params to sql>);
  
• Query
• RowMapper
• Interace in Spring framework which needs to be implemented
• It maps resultset into Object of class that we create
• mapRow() to be implemented
•  
  
• config.xml
  

Spring Boot

• Challenges addressed
• what maven arche type to be used
• what maven dependencies to be used
• configuration file
• what server to be used
• Spring boot 
• easier to get started with Spring development
• minimize amount of manual configuration
• auto config based on props file and jar class path
• embedded server
• Overall- It is self-contained unit
  
• Spring initializer
• create starter project, select dependencies,
  
• https://start.spring.io/
•  Creates Maven/gradle project
• Import project into IDE
• One can run the app from command line and IDE
• java -jar <jar name>
  
• Source code generated by spring boot initializer
• import org.springframework.boot.autoconfigure.SpringBootApplication
  @SpringBootApplication  -> This is composed of other annotations
  
• The annotation composed of @EnableAutoConfiguration
  @ComponentScan
  @Configuration
• SpringApplication.run
• Creates application context, register all beans
• starts embedded tomcat server
• application.properties for Custom properties
  
• Change default port
  server.port=8181
• Properties defined here can be referenced in using
  @Value("${<property name>}")
  private String var1
• Spring boot dev tools
• Automatically restart application when code is changed
• simply add dependency spring-boot-devtools
• Spring boot Actuator
• Exposes end points to monitor application
• Easily get dev ops functionality out of box
• simply add dependency spring-boot-starter-actuator
• ../health
  ../info
• Run from Command line
• java -jar <application.jar>
• mvnw:spring-boot:run

SpringBoot - Datasource configuration for Hibernate 

• application.properties
• spring.datasource.url
• spring.datasource.username
• spring.datasource.password
• Spring boot will automatically create beans for DataSource and EntityManager
•  
  

Prometheus

• The Prometheus monitoring system and time series database
• To monitor workloads
• open source monitoring solution
• Scape data/metrics using http end points
• All data is stored as TimeSeries
• Every time series is identified by metric name and a set of key-value pairs, called labels
• 
  
• Types of metrics
• Counter
• Value that only goes up
  
• Gauge
• Numeric value that can go up and down(like cpu load)
  
• Histogram
• Sample observations(request duration, response sizes)
  
• Summary
• PromQL
• Provides builtin operators and functions
• expressions over time-series vectors
• Querying metrics
• Instant Vector
• single sample for each time series - all sharing the same time stamp
• eg: node_cpu_seconds_total
  
• Range Vector
• range of data points over time for each time series
• eg: node_cpu_seconds_total[5min]
• Scalar
• Simple numeric floating point value
• Service discovery
• Automatic detection of devices and services offered by these devices on a computer network
• Exporters
• Export third party metrics  to Prometheus metrics

Alerting

• Alerting rules
• Rules live in Prometheus server config
•  
• Alert manager