Author Archives: cyberaka

About cyberaka

I am an experienced Senior Solution Architect with proven history of designing robust and highly available Java based solutions. I am skilled in architecting designing and developing scalable, highly available, fault tolerant and concurrent systems which can serve high volume traffic. I have hands on experience in designing RESTful MicroServices architecture using Spring Boot, Spring Cloud, MongoDB, Java 8, Redis and Kafka. I like TDD (JUnit), BDD (Cucumber) and DDD based development as required for my projects. I have used AWS primarily for cloud based deployment and I like developing cloud enabled POC as a hobby in my spare time. I have deigned and developed CI/CD pipeline using Jenkins and leveraged Docker, Kubernetes for containerizing and deploying some of my applications. I am highly experienced in creating high performing technical teams from scratch. As an ex-entrepreneur I am very much involved in the business side of the IT industry. I love interacting with clients to understand their requirements and get the job done.

Setting up MySQL docker instance

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In order to setup a fully functional MySQL server via docker I use the following consolidated command:

docker run \
--detach \
--name=mysql \
--env="MYSQL_ROOT_PASSWORD=abcd1234" \
--publish 6603:3306 \
--volume=~/Docker/mysql/conf.d:/etc/mysql/conf.d \
--volume=~/Docker/mysql/mysql-datadir:/var/lib/mysql \
mysql

The advantage of the above approach is that the configuration files can be defined under ~/Docker/mysql/conf.d folder on my system and it will be picked up whenever I bootup this instance. The second thing is that all information written by this instance will be stored outside of VM in the path ~/Docker/mysql/mysql-datadir on my system. So In case this VM goes away due to some unexplained reasons I can still bootup another docker instance of MySQL and point it to this data directory.

Maven: Installing / adding local jar into your local maven repository

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I needed to install a local jar file into my laptop’s local maven repository and found this article. I used this approach to install this jar file in my repo:

mvn install:install-file -Dfile=my-model-1.2.1.jar -DgroupId=com.cyberaka.my.package -DartifactId=my-model -Dversion=1.2.1 -Dpackaging=jar -DgeneratePom=true

This duly added the local jar file under appropriate group id and artifact id inside my maven repository and I was able to refer to this dependency through my project’s pom.

 

Using NGINX for Proxy Pass

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Lets say I have two servers running on my laptop
1. http://localhost:3000 – This is the UI
2. http://localhost:4000 – This is the web services API

So now I need to setup something like this:
1. http://localhost/ – This should point to UI
2. http://localhost/api/ – This should point to web services API

To set this up I have used NGINX and added this section in the “server” section of the nginx.conf file. On my Mac system this file is located at: /usr/local/etc/nginx/nginx.conf

location /api/ {
proxy_set_header X-Forwarded-Host $host;
proxy_set_header X-Forwarded-Server $host;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_pass http://localhost:4000/;
}

location / {
proxy_set_header X-Forwarded-Host $host;
proxy_set_header X-Forwarded-Server $host;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_pass http://localhost:3000/;
}

To reload NGINX I use the “-s reload” parameter for nginx. On my Mac I execute this command:
/usr/local/Cellar/nginx/1.10.0/bin/nginx -s reload

User input in shell script

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I needed to write a small shell script which would allow me to make some decision based on user choices. I needed the user to specify Yes, No or Cancel for an operation. The following piece of hack does the job well.

#! /bin/bash

# define constants
declare -r TRUE=0
declare -r FALSE=1

user_choice() {
local str="$@"
while true
do
# Prompt user, and read command line argument
read -p "$str " answer

# Handle the input we were given
case $answer in
[yY]* ) return $TRUE;;

[nN]* ) return $FALSE;;

[cC]* ) exit;;

* ) echo "Y - Yes, N - No, C - Cancel. Please choose valid option.";;
esac
done
}

if user_choice "Execute Job 1? "; then
echo "Executing Job 1.."
fi
if user_choice "Execute Job 2? "; then
echo "Executing Job 2.."
fi

The following links were referred to achieve this little script:
http://linuxcommand.org/wss0090.php
https://bash.cyberciti.biz/guide/Returning_from_a_function
http://alvinalexander.com/linux-unix/shell-script-how-prompt-read-user-input-bash

Measuring UTF-8 character size

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Lets say I type something in Hindi and the outcome is listed below:

तीन व्याकितियों की औसत आयु ३३ वर्ष है.

In Hex View it will look like:

e0 a4 a4 e0 a5 80 e0 a4 a8 20 e0 a4 b5 e0 a5 8d e0 a4 af e0 a4 be e0 a4 95 e0 a4 bf e0 a4 a4 e0 a4 bf e0 a4 af e0 a5 8b e0 a4 82 20 e0 a4 95 e0 a5 80 20 e0 a4 94 e0 a4 b8 e0 a4 a4 20 e0 a4 86 e0 a4 af e0 a5 81 20 e0 a5 a9 e0 a5 a9 20 e0 a4 b5 e0 a4 b0 e0 a5 8d e0 a4 b7 20 e0 a4 b9 e0 a5 88 2e e0 a4 85 e0 a4 97 e0 a4 b0 20 e0 a4 89 e0 a4 a8 e0 a4 95 e0 a5 80 20 e0 a4 86 e0 a4 af e0 a5 81 20 e0 a5 a8 3a e0 a5 a9 3a e0 a5 aa 20 e0 a4 95 e0 a5 87 20 e0 a4 85 e0 a4 a8 e0 a5 81 e0 a4 aa e0 a4 be e0 a4 a4 20 e0 a4 ae e0 a5 87 e0 a4 82 20 e0 a4 b9 e0 a5 8b 2c e0 a4 a4 e0 a5 8b e0 a4 b9 20 e0 a4 89 e0 a4 a8 e0 a4 ae e0 a5 87 20 e0 a4 b8 e0 a5 87 20 e0 a4 b8 e0 a4 ac e0 a4 b8 e0 a5 87 20 e0 a4 ac e0 a5 9c e0 a5 87 20 e0 a4 95 e0 a5 80 20 e0 a4 86 e0 a4 af e0 a5 81 20 e0 a4 95 e0 a4 bf e0 a4 af e0 a5 8d e0 a4 a4 e0 a4 a8 e0 a5 87 20 e0 a4 b5 e0 a4 b0 e0 a5 8d e0 a4 b7 20 e0 a4 b9 e0 a5 8b e0 a4 97 e0 a5 80 3f

The main thing to notice here is that every hindi character is starting with the byte “E0”. This is basically a code point which identifies the code size of the UTF-8 character. The following table appropriate highlights it:

Binary    Hex          Comments
0xxxxxxx  0x00..0x7F   Only byte of a 1-byte character encoding
10xxxxxx  0x80..0xBF   Continuation bytes (1-3 continuation bytes)
110xxxxx  0xC0..0xDF   First byte of a 2-byte character encoding
1110xxxx  0xE0..0xEF   First byte of a 3-byte character encoding
11110xxx  0xF0..0xF4   First byte of a 4-byte character encoding

Reference: https://stackoverflow.com/questions/5290182/how-many-bytes-does-one-unicode-character-take/33349765#33349765

 

Embedding images directly into HTML

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I needed to email an HTML report and I was not happy with the fact that we have to create zip file containing the HTML, Images etc. I knew it was possible to embed base64 data directly into HTML I started looking for some PoC. My search took me to an online base64 encoder and decoder. This gave me the idea to convert the external image files into base64 string and embed it directly into HTML. On some search I landed up Apache Commons Codec Library which contains a Base64 class which can be used to covert an input stream into a base64 string.