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.

Taking backup zip from multi-module Java project

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I like to keep an archive of my code on a monthly basis. I wrote a small bash script to create zip out of my multi module Java projects. It gets the job done and can be improved to include resources and test folders as well. As of now I am only interested in the Java code zip backup.

!/bin/bash
 if [ -d "combined" ]; then
     echo "Removing existing zip files in combined .."
     rm combined/*.zip
 else
     echo "Creating combined folder.."
     mkdir combined
 fi
 for d in */ ; do
     if [ -d "$d/src/main/java" ]; then
         var="$(echo $d | sed 's/.$//')"
         echo "Processing $var .."
         cd $d/src/main/java
         zip -r ../../../../combined/$var.zip com
         cd ../../../..
     else
         echo "Ignoring .. $d"
     fi
 done

ssh_exchange_identification: read: Connection reset by peer

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I recently upgraded my Mac Desktop and I noticed a strange problem that I was not able to SSH into my desktop from my laptop. I ultimately found out that the SSH setup that came with MacOS was having some issue as when I did ssh user@localhost on the desktop I got the same error:

ssh_exchange_identification: read: Connection reset by peer

I ended up tailing the system log using the following command:

sudo tail -f /var/log/system.log

I observed the following entries in the log whenever a SSH was attempted. 

com.apple.xpc.launchd[1] (com.openssh.sshd.[UUID][NUM]): Service exited with abnormal code: 1

It was clear that there was setup issue with the SSH that came with default MacOS installation. So I decided to spawn a separate SSH instance and watch it’s log:

sudo /usr/sbin/sshd -d -p 2222

This command showed up a lot of issues related to file permissions.

Permissions 0644 for '/etc/ssh/ssh_host_dsa_key' are too open.
Permissions 0644 for '/etc/ssh/ssh_host_ecdsa_key' are too open.
Permissions 0644 for '/etc/ssh/ssh_host_ed25519_key' are too open.

I fixed these permission issues by changing their permission to 400:

sudo chmod 400 /etc/ssh/ssh_host_dsa_key
sudo chmod 400 /etc/ssh/ssh_host_ecdsa_key
sudo chmod 400 /etc/ssh/ssh_host_ed25519_key

After this change the following command succeeded and I was able to do successful SSH connection to port 2222.

sudo /usr/sbin/sshd -d -p 2222

So I killed this process and decided to restart SSH:

sudo launchctl unload /System/Library/LaunchDaemons/ssh.plist 
sudo lsof -i:22
echo $?
sudo launchctl load /System/Library/LaunchDaemons/ssh.plist 

Once SSHD was restarted I could successfully do logins using ssh user@localhost from Desktop as well as remote login via SSH from my laptop. 

Prettify JSON on Terminal

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I love using curl command on my Mac terminal to debug my REST endpoints. However the REST call JSON output used to come in a blob of text which required further formatting in an Editor like Visual Studio Code. To allay this problem I ended up installing “jsonpp” using homebrew.

brew install jsonpp

So now I just pipe the output of my curl command to the jsonpp program and I get a fully formatted JSON.

$ curl http://localhost:8080/test | jsonpp
{
"year": 2018,
"month": 2,
"worked": 18,
"leaves": 2
}

 

 

Curl Command New Line Post Output

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I like to use curl instead of UI tools like Postman for debugging my RESTful web services traffic whenever possible. I however didn’t like my output being messed up by the bash prompt being suffixed to the output. Something like the following:

$ curl -H "$auth_token" http://localhost:8080/xyz/abc-efg
["-","A","B","C","D","E"]$

So basically what I needed was to have a new line forced after the curl output. A quick search on internet yielded this article. So I executed the following command on my terminal.

$ echo '-w "\n"' >> ~/.curlrc

After doing this when I execute the same curl command I get the following output.

$ curl -H "$auth_token" http://localhost:8080/xyz/abc-efg
["-","A","B","C","D","E"]
$

So now the bash prompt is actually coming on a new line by default!

Validating Signature in PDF documents in Acrobat Reader

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I received a digitally signed document from a trusted source. However when I proceeded to take a print it came out with “Signature Not Verified” in place of the signature field. This was not going to work so I did some googling and found out this link. It basically allowed me to validate the signature and take a printout with “Signature Valid” in place of the digital signature.