Flevo CFD

Ultimate Guide to Tunneling in Linux

Fri, 23 Aug 2024 09:03:53 +0200

There are cases where your machine does not have access to the destination server, or you don’t want to expose the destination server to the internet. In these cases, you can use a relay server to tunnel the traffic to the destination server.

A relay server simply forwards the incoming traffic to the destination server and forwards the response back to the client.

For the sake of this article, we want to relay openvpn traffic from machine A to machine B.

Links of the Month - August

Fri, 09 Aug 2024 16:23:10 +0200

tldr

I can’t live without tldr. It shows you the most common commands of a program.

Forgot how to use tar? Just type tldr tar and you will see the most common commands.

Squoosh

Compress your images with this tool. It supports multiple formats and you can see the output in real time.

bmon

Network bandwidth monitor. It shows the traffic in real time. don’t forget to run with sudo to see all the interfaces.

Dream

Mon, 01 Jul 2024 23:18:57 +0200

Last night I woke up at midnight. A thought woke me up. When I became conscious, the thought became clear.

“Someday you will be gone. You will disappear from existence. What’s the big deal about doing what you want?”

One day will be my/your last day. What a sharp, transparent, and honest fact that is, isn’t it? And yet we do the same BS things day in and day out.

The Path

Sat, 22 Jun 2024 22:59:29 +0200

I know what makes me happy. I know what I need to do, but I don’t. I can’t.

What’s this belief inside me that stops me from doing things?

This belief definitely did good for me, maybe when I was a kid or until high school, but not anymore.

I don’t want it anymore. I just don’t want it. I’m sick of it. How am I supposed to cut it off?

Failure

Thu, 06 Jun 2024 22:42:51 +0200

Bad days are inevitable. But hold on. Why do you call them bad? Because things didn’t go well? You didn’t get what you wanted? It was bizarre? It was an awkward situation? Someone disrespected you?

Let’s flip the story. What would you gain if things went the way you wanted? Would you learn anything in that case?

From which situations do you learn something? It’s most likely the bad ones.

Progress

Tue, 04 Jun 2024 20:31:08 +0200

Last year at this time, I started playing squash. My level has grown by 2.5 points. My position in the club was 60, and now it’s 23.

You can see my performance diagram in the club games. It’s not like a straight line with a positive slope, is it? It’s not like movies where you master any skill in 3 months.

In the beginning, when I missed a shot, I would beat myself up. “You’re stupid. You suck. You’ll never learn.” But as time passed, I figured out that it’s just a skill. There’s nothing wrong with me. It’s just a matter of practice. Some people learn faster? Good for them! What does it matter to you how quickly you learn it?

You Are Me

Thu, 30 May 2024 18:43:27 +0200

There’s a principle that suggests nothing is about you in the context of human interactions.

When someone doesn’t treat you well, it’s not about you. Don’t take anything personally.

Behave and treat everyone like you’re behaving and treating yourself.

You take out the garbage and see someone at the door. Look at them in a way you’re looking at yourself. Say hi in a way you’re greeting yourself.

Words don’t matter, do they? “Oh, I don’t speak their language; I never can communicate with them.” Really! Do you believe the nonsense you just said?

If I .... then I'll ...

Wed, 29 May 2024 20:49:04 +0200

I’m fine, I’m good. How can I not be?

Listening to house music with my new sound system. What more do I need? I don’t need anything, no one does. You already have what you need, don’t you?

You think acquiring things, moving to another location will satisfy your needs, but guess what, it doesn’t.

I’m not saying you shouldn’t get things or go traveling. I’m saying you should not condition your mood to anything external (if you already live in a peaceful environment and your basic physical needs are satisfied).

Give Me Love

Mon, 27 May 2024 17:07:20 +0200

What if you could give yourself the love you always wanted?

Can you imagine how much energy it pumps into your brain when someone tells you “You are so smart,” “You are so weird,” “You are so funny,” “I’m sure you’ll be successful someday,” or “You {what the f you want to hear or get approval for}”?

I tell you what you want. Please be happy about tomorrow, about waking up. I’ll tell you anything you want.

Cachew + m&m = the SHIT

Sat, 25 May 2024 20:53:06 +0200

I don’t know why I’m publishing this stuff.

I’m sick of my life. I’m not doing anything fun anymore. I used to, but not since I moved to another country and got stable in life.

I just don’t want to play the fool, challenging myself.

I love breaking norms in society, speaking my mind in formal corporate meetings, and taking down the boss.

Pointing out the white (or pink) elephant in the room cheers me up. It makes me smile while sitting on the metro, looking at the station sign.

A Roommate and Brain Booster Pills

Wed, 22 May 2024 18:57:22 +0200

I’ve got a roommate. He’s a young fella who was born in the Netherlands, but he doesn’t think he’s Dutch!

I bought the house a few months ago. Money was tight, so I thought, why wouldn’t I rent out a room? It wasn’t my only reason. I was a bit lonely. Not a bit, but a lot! I just wanted some company.

His girlfriend came over a few nights ago. They had quite a lot of fun (if you know what I mean!). I was a bit jealous. Not a bit, but a lot! Usually, people in these situations think about their ex(es), but how can I? (If you know what I mean!)

Handle Timezones in Django Rest Framework

Wed, 22 May 2024 17:59:46 +0200

What is Timezone?

A timezone is a designate area on the globe that has the same standard time. Timezones are usually defined by the number of hours that they are offset from Coordinated Universal Time (UTC).

For example “22:10:00 UTC+2” means that the time is 22:10:00 in the timezone that is 2 hours ahead of UTC.

GMT stands for Greenwich Mean Time. It is the time at the Royal Observatory in Greenwich, London. GMT is the same as UTC.

ADHD

Wed, 22 May 2024 13:06:01 +0200

I think I have ADHD. I can’t sit still for a long time. I kind of feel like this guy in the video below.

Your browser does not support the video tag.

Cross-Site Request Forgery (CSRF): A Simple Explanation

Sun, 21 Apr 2024 17:16:24 +0200

Cross-Site Request Forgery (CSRF) is a type of attack that occurs when a malicious website tricks a user into submitting a request to a website that they are authenticated to. The attacker can use this request to perform actions on the website on behalf of the user, such as changing their password, deleting data, etc.

Since the browser automatically sends cookies with every request to a website, the request will be authenticated using the user’s cookies. This means that the website will treat the request as if it came from the user, even though it was initiated by the attacker.

Cross-Origin Resource Sharing (CORS): What is it? How does it work?

Sun, 21 Apr 2024 11:28:40 +0200

CORS is a security mechanism that allows web applications to make cross-origin requests.

Cross-origin requests are requests that are made from one domain to another domain.

By default, web browsers prevent cross-origin requests for security reasons. However, CORS allows web applications to make cross-origin requests by adding specific headers to the HTTP response.

CORS relaxes the same-origin policy to enable web applications interact with each other in a secure manner, while not protecting web applications from specific attacks.

Upload files to AWS S3 using Presigned URLs in Python

Tue, 16 Apr 2024 17:33:42 +0200

Object storage is the ideal solution for handling large amount of unstructured data that don’t change that often (are static). it’s relatively fast, cheap and easy to scale.

In object storage systems, files are called objects. a unique identifer is assigned to each object which is the object name. there’s no hirearchy like a file storage in your operating system has. you just need to know the object name to retrieve it.

Do You Think Python Can Run Two Tasks simultaneously?

Sat, 16 Mar 2024 21:55:57 +0100

In this post, I want to talk about parallel programming, but before that, I need to define a few terms.

Types of tasks

Sync

A sync task is dependent on another task, meaning it needs to synchronize with that task and wait for it to finish before it starts its own work. For example, consider the task of moving to a room. it consists of two tasks of opening the door and going into the room. if you don’t open the door you can’t get into it (there’re other ways but just take it as an example).

Decorators in Python

Wed, 14 Feb 2024 21:50:57 +0100

Decorator is a function that returns another function. the goal of decorators is to add logic to existing functions. common use cases could be log the output, check the permissions before running the function and …

Take the following code as an example

def log(func):
 def wrapper(*args, **kwargs):
 print(f"executing {func} with arguments {args} {kwargs}")
 return func(*args, **kwargs)
 return wrapper


def test():
 print("hello")

test = log(test)

The log function is a decorator. it takes a function as an argument and returns another function. the returned function is the one that will be executed when we call test. the wrapper function is the one that will be executed when we call test. it logs the arguments and the function name before executing the function.

Mutable and Immutable Variables and Namespaces in Python

Thu, 08 Feb 2024 21:26:48 +0100

Namespace is a place where a variable is stored. There are four namespaces in Python as local, nested (or enclosing), global and built-in.

What type of programming language is Python?

Is it an interpreted or compiled language? there’s an assumption that Python is an interpreted language meaning an interpreter (like CPython which is the dominant interpreter in the ecosystem) runs the code line by line.

It’s versus compiled language which a compiler compiles the entire program into machine code. I don’t want to get into comparing them.

Configure Nginx with uWSGI

Sun, 04 Feb 2024 18:58:33 +0100

Ningx and uWSGI are powerful tools on their category. Nginx is a web server and reverse-proxy that can serve static files, change the request, cache content, apply rate limiting and lots of features. on the other hand uWSGI is an application server. it runs a web application, when a request comes in handles it and passes the response.

There’s a specification called WSGI (Web Server Gateway Interface) which describes how web servers and Python web applications should communicate with each other. uWSGI has its own protocol called uwsgi which implmenets WSGI.

Streaming Data with SSE Protocol in Python

Sun, 28 Jan 2024 20:42:45 +0100

HTTP Server Push or HTTP Streaming is a communication between the server and the user where the user only needs to establish a connection, and after that, data is sent to them without the need for the user to make requests.

There are several protocols for streaming data

HTTP Long Pulling or Hanging GET

In Long Pulling, when the user sends a request, the server checks if there is new data to send. If there is, it sends the data, and the connection closes, similar to a regular request. If there is no new data, it keeps the connection open until new data is ready, then sends it, and closes the connection.

How Read Environment Variables in Single Page Applications

Sun, 07 Jan 2024 17:47:58 +0100

Recetly I’ve been working on adding Sentry to our UI which is a Single Page Application. We’re using systemd and podman to run our services.

to initialize Sentry we need some configuration which needs to be passed at the runtime but the SPA is a static javascript codebase which can not have access to environment variables.

To tackle it I came across a few solutions.

#1

We can use placeholders in the Sentry initialization code and replace them with actual values in the service file.

High Availability on Heroku

Tue, 02 Jan 2024 09:40:25 +0330

Our integration APIs are hosted on Heroku. these are the APIs that are consumed by our partners. there’s only one active instance per each API. that sounds like a single point of failure, doesn’t it? we planned to increase the number of servers to two in order to make them high available.

What is Heroku

Heroku is a Platform as a Service (PAAS). they provide you the hardware and software and you just need to write the code

Quick Debugging of Programs in Linux

Mon, 01 Jan 2024 20:29:22 +0100

In Linux, to inspect what a program is doing, which files it is accessing, etc., and overall, to debug it to identify where the issue lies, you can use GDB (GNU Debugger) and strace.

The following command is generally used for launching your program

gdb -ex r --args {program name} {program argument} {program argument} ...

For example

gdb -ex r --args python3.6 main.py
gdb -ex r --args mysql -uroot -proot

Here, -ex executes a GDB command, and we specify r to run the program until it encounters an error or a breakpoint.

Find Public IP Address of your System

Mon, 01 Jan 2024 20:26:33 +0100

The following websites show your system’s Public IP

The other way is to use Cloudflare DNS

dig +short txt ch whoami.cloudflare @1.0.0.1

How we Obtained 500 Thousand Domains Whois Information in 10 Days using Python and Tor

Wed, 13 Dec 2023 18:27:00 +0100

Before reading, take a look at Do you know the difference between Registrar, Registry, and Registrant? to have a better understanding of this post.

In my latest project, I had to retrieve Whois information for a total of 500 thousand domains with various TLDs.

When I fetched Whois information for some domains, I realized it didn’t provide complete information. That’s when I became familiar with the concepts of thick Whois and thin Whois.

Do you know what Registrar, Registry, and Registrant are?

Tue, 12 Dec 2023 20:07:53 +0100

Today, I want to talk about the differences between Registry, Registrar, and Registrant.

A domain consists of several parts, and the part we are dealing with today is the extension or TLD (Top Level Domain) of the domain.

TLDs are divided into two groups

gTLD (generic TLD)

These are extensions with three or more characters, such as com, net, org, asia, rocks, etc.

ccTLD (country code TLD)

These are country-specific extensions, such as ca, tr, ir, etc.

Photos

Sat, 09 Dec 2023 12:42:44 +0100

Running Processes in Python with the Subprocess Module

Tue, 05 Dec 2023 23:10:49 +0100

To execute processes in Python, you can use the os.system and subprocess modules. In this post, we will become familiar with the subprocess module.

Take a look at this example

from subprocess import Popen

process = Popen(['ls', '-l'])
process.communicate()

The above code executes ls -l command in the operating system.

Popen initiates the execution of the command, but it does not wait for the process to finish. This is where the communicate method comes in, which waits for the process to complete.

What is PYTHONPATH

Mon, 04 Dec 2023 20:06:52 +0100

The PYTHONPATH is a variable in Python that the interpreter uses to locate modules by searching through the paths specified in sys.path.

sys.path is a list that includes, in order

The directory of the script (if applicable).
Paths specified in the environmental variable PYTHONPATH.
Other paths depending on the Python installation on your system.

So, when you import a module, Python searches through these paths in order to find the module.

Linux Shared Libraries

Wed, 29 Nov 2023 15:49:15 +0100

Libraries are ready-made codes that programs utilize, eliminating the need for programmers to implement them.

In Linux, these files are called Shared Libraries or Shared Objects with the extension so (in Windows, the extension is dll).

Program developers have two ways to use their desired libraries

Embed them directly in their code, known as Static Linking.

Request them from the operating system, known as Dynamic Linking. Due to the increase in program size and other issues, Dynamic Linking is usually preferred. In this post we’re looking into them.

Bash Sartup Files

Sat, 25 Nov 2023 18:56:52 +0100

Shell is a tool through which we can execute a series of commands in a new operating system. There are several shells, such as sh, bash, zsh, and fish shell.

In this text, we want to see what files bash loads when we open the terminal. With this knowledge, we can place our custom variables or scripts in appropriate files so that they are identified or executed whenever bash starts.

Concurrent Processing with xargs and parallel

Wed, 22 Nov 2023 20:01:32 +0100

You might have encountered situations where you needed to execute an operation or a program on multiple files.

The first potential issue is that the program may only accept one file as input, such as mv which takes only one input and produces one output.

Now, assuming our program accepts a list of files, the second potential issue is that it might process the files sequentially rather than concurrently, like the tar compression program.