DevOps Prerequisite (Part 3): Application basics (NodeJs & Python)

I general we have compiled and interpreted languages

For compiled codes, it's first developed, then compiled and then run. They don't work in different system.

For interpreted ones, it is developed and then run

But it does compile into bytecode and run in the process "run" . We don't have extra compiler stage rather it is done in the "run" step.

This is how a python code gets executed

we write a code which is compiled to a bytecode and then the interpreter translate that to machine code which the computer understand.

With the use of Python VM, we can compile our byte codes very easily

Java
This is how we can install java in our linux based systems

Now we can see a word "jdk". What's that?

JDK is a tool which consists of all tools required to develop , build and run the codes of java

For example, to develop java codes, jdb, javadoc etc are used.

You can see the list of tools installed within jdk directory

It's kept in the /bin file though

Lab

Let's install Java 20 inside /opt folder
sudo curl https://download.java.net/java/GA/jdk20/bdc68b4b9cbc4ebcb30745c85038d91d/36/GPL/openjdk-20_linux-x64_bin.tar.gz --output /opt/openjdk-20_linux-x64_bin.tar.gz

sudo used for administrative access, curl for the download and the original download link is "https://download.............." and then we saved the result to /opt folder in the name of "openjdk-20_linux-64_bin.tar.gz"

So, we installed the compressed file (.gz)

Now, let's uncompress

sudo tar -xf /opt/openjdk-20_linux-x64_bin.tar.gz -C /opt/
tar is used to decompress and used the folder location /opt/opejdk_... and saved the files in /opt folder

Once done, we can check these files available in the folder

Now, it's installed as it's decompressed. We can check the version by going into the jdk-20 folder's bin folder

How to build in Java?

This is how a typical compiling file (MyClass.class) might look

But a typical file might have dependencies and other class files to compile

Which we can compress using a jar command.

Here jar cf is followed by jar file name and all class files and dependencies we need to compress

The informationabout the jar file is saved in META-INF folder

Using the javadoc we can then document our java file so that others can read that

SO, as a whole we can manually compile , package and document our MyClass file

But there are tools for java (Maven, Gradle, ANT) which can do these process for us

For example, using the ANT we can provide the compiliting (javac), documentation (javadoc), package (jar) them

here you can see for compiling we have
<javac srcdir='/app/src" destdir='/app/build"
Here srcdir is the source folder where our code is and we have to compile that to /app/build folder

For documentation,

For packaging using jar,

For Maven, it's almost the same

And for Gradle,

NodeJs
Earlier we had this as a website using HTML and CSS:

But now we have this one:

JavaScript (Js) made this difference.

Here NodeJs is server site JavaScript environment

This is how we can install nodeJs in centos:

NPM (Node Package Manager)

So, nodejs and npm is not same but npm manages nodes .

Modules

Python

Versions:

This is how this code works:

PIP (Python package manager)

Installing something using pip does this:

Here we have 2 python versions enabled here and we found out that currently pip is enabled on version 2.
So, if we install this flask package, we will create this file under this.

Checking paths :

Importing python packages in to codes:

Run required all files using a txt file or manually.

You can manually installed dedicated versions too.

You can also upgrade and delete them.

Moreover, these are other ways to run python (.py) files.