Docker - getting started (very basics)

Docker-Overview

Docker makes much easier to deploy applications. It helps to resolve one main problem - “works in my machine problem”. 

Getting started

• Download docker from here for your OS: 

• https://www.docker.com/community-edition#/download

• Install the docker DMG if Mac.

• Login to docker once it is installed. 

• Open terminal and execute the following: 
• Docker -version
• Docker run hello-world
• Docker run —name deiveehello hello-world
• Docker run -it —name mylinuc-container ubuntu bash

For a hands on video - click here

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Some basic docker commands

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Docker images // lists all images

Docker ps // lists all process

Docker run —help

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Running a docker using simple ubuntu image

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docker ps -a -f status=exited -q

docker rm $(docker ps -a -f status=exited -q)

docker run -it --name my-linuc-container-1 ubuntu bash

docker run -it --name my-linux-container1 --rm -v /Users/deiveehannallazhagappan/Documents/volumes/project1:/my-data ubuntu bash

Cd my-data

Touch aa.txt

Ls

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Creating image from a local docker file.

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• Create a docker file with the following content.

FROM ubuntu

CMD echo "Hello Deivee"

• Run the following command. 

docker $docker build -t deivee-tracker-image .

Sending build context to Docker daemon  2.048kB

Step 1/2 : FROM ubuntu

 ---> f975c5035748

Step 2/2 : CMD echo "Hello Deivee"

 ---> Running in 10c68c4eb454

Removing intermediate container 10c68c4eb454

 ---> b235e94e39b4

Successfully built b235e94e39b4

Successfully tagged deivee-tracker-image:latest

docker $docker images

REPOSITORY             TAG                 IMAGE ID            CREATED              SIZE

deivee-tracker-image   latest              b235e94e39b4        About a minute ago   112MB

ubuntu                 latest              f975c5035748        4 weeks ago          112MB

hello-world            latest              f2a91732366c        4 months ago         1.85kB

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Run the docker image

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docker $docker run deivee-tracker-image

Hello Deivee

docker $docker ps -a

CONTAINER ID        IMAGE                  COMMAND                   CREATED             STATUS                      PORTS               NAMES

9a65c141ec46        deivee-tracker-image   "/bin/sh -c 'echo \"H…"   5 seconds ago       Exited (0) 4 seconds ago                        optimistic_stonebraker

0e922f16f866        ubuntu                 "bash"                    12 minutes ago      Exited (0) 11 minutes ago                       tracker

be1311055d15        ubuntu                 "bash"                    23 minutes ago      Created                                         my-linux-container

77447d4d6c02        hello-world            "--name deiveehello"      12 hours ago        Created                                         elastic_wozniak

For a more hands on video on getting started with Docker, click here.
https://www.youtube.com/watch?v=hfL0USkCmZ0&t=305s

Java 8 - new important features

Java 8 has included a lot of new features, this post will explain a few important features. 

1. Lamda Expressions. 
2. Functional Interfaces. 
3. Streams
4. Nashorn

Other features. 

• Date and time api changes. 
• Foreach. 

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Lamda expressions

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Lamda expression is a function with no name and with implementation. 

A basic expression format would be..

(x, y) -> x + y

Where (x, y) are the function input parameters. And x+y is the statement executed by the function and returned. 

Example: 

FileFilter filterLamda = (File pathName) -> pathName.getName().endsWith(".png");

File dir = new File("/Users/deiveehannallazhagappan/workspace/xplore-java/supporting");

File[] files = dir.listFiles(filterLamda);

for (File f: files) {

    System.out.println("f = " + f);

}

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Functional Interfaces

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Functional interfaces are interfaces that have only one abstract method in it. 

Example: 

@FunctionalInterface

public interface TestFuncInterface {

    public void testmethod();

default void testdefaultmethod(){

         System.out.println(“default method“);

     }

}

Lamda expressions can be used to represent the instance of a functional interface. 

Note: 

• You can add default methods .

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Streams

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Streams are new feature introduced in Java 8 to simplify the logic required to process data - filtering, transforming data etc., 

For example, the below example does the following

• Creates a new array list from 1-30
• Creates a stream of integers. 
• Filters the list by extracting only no.s divisible by 3 and converts them into a integer array. 

Stream example: 

List<Integer> list = new ArrayList<Integer>();

for(int i = 1; i< 30; i++){

    list.add(i);

}

Stream<Integer> stream = list.stream();

Integer[] evenNumbersArr = stream.filter(i -> i%3 == 0).toArray(Integer[]::new);

System.out.print(evenNumbersArr);

Why streams: reduce complexity, less code. 

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Nashorn

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Nashorn is a javascript engine which allows the java applications to interact with the JS code. 

ScriptEngineManager sem = new ScriptEngineManager();

ScriptEngine engine = sem.getEngineByName("nashorn");

engine.eval("print('deiveehan')");

You can also execute an external script instead of using inline js code. 

engine.eval(new FileReader("/Users/deiveehannallazhagappan/workspace/xplore-java/supporting/js/deiveescript.js"));

You will get the output of the js code when you run the java application. 

Refreshing - Git basics

This post explains some of the basics of git (a simple refresher post to GIT commands).

Git clone <git url> download a project from git remote repository

init

add <file> or .

commit -m <commit message> (Commit files to local repository)

status (list all new and modified files)

diff (Shows files modified)

fetch: fetches the remote repo into the local repo, but does not merge

pull: does and fetch and also does the merge into the local repo. 

Remote: lists the remote

git remote

git remote -v

Log: logs all changes

git log

git log —all

git log —all —oneline —decorate —graph

SCENARIOS:

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# Local folder to Git remote. 

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Steps to commit an already existing local project to git. 

git init

git add README.md

Git commit -m “Initial commit”

Create a repository in git and get the 

git remote add origin git@github.com:deiveehan/<reponame.git>

Git push -u origin master. 

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# Create a branch from command line.

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git branch —list (shows all the branches). 

git checkout -b develop (creates a local branch called develop)

change a file

perform git add and commit to the local code.

git push —set-upstream origin develop

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# Switching branches.

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Git branch (shows local branches)

Git checkout develop

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# Merging with parent branch (say develop)

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Master

• Develop
• A

commit A changes to local repository

git checkout develop

git merge A

git push

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# Deleting remote branch

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git branch -d A (Delete references of local branch)

git push origin -d A (delete remote branch)

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