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Networking on Willem's Blog

Linking Lemmid Store with kitchens

Integrating with external systems that you don't control

June 12, 2020
Designing backend servers to connect with external services is challenging as you need to take into account unreliability and unpredictability.

As part of the food ordering app I am building, I needed to design a reliable way to link the app to external systems. These external systems are beyond my direct control and include different checkout registers, kitchen management systems and ticket printers. Read along for more on designing for the unknown and unreliable.

Traffic shaping using iptables and tc

Limiting outbound network bandwidth per client IP-address

Apr. 1, 2020
This month I responded to an automated alert indicating excessive bandwidth usage on a server, requiring me to apply traffic shaping to mitigate the traffic.

Last month I received an automated alert indicating excessive bandwidth usage, usually a sign of trouble. When this happens, you should follow a standard incident procedure, trying to isolate the source of the traffic before shutting it down. The cause of this incident was not what I expected however... requiring a different kind of mitigation than a simple blockade.

Your own addressbook and calendar cloud

Share contacts, agendas and tasks with CardDAV/CalDAV

Feb. 28, 2020
You can setup a CardDAV/CalDAV server to manage your own contacts, addressbook, agenda and task data and share it between your devices.

If you use different devices and computers to get things done, you might want to synchronise contacts, agendas and tasks. You can use any of the 'big cloud' services for this, like Apple iCloud, Microsoft Office 365 and Google Gmail. But, if you prefer not to share your addressbook and calendar with big American companies, you can do it yourself.

Building a professional 72TB NAS

Configuration and installation of an HPE ProLiant DL380 server

Nov. 22, 2019
This month I installed a professional HPE ProLiant DL380p server in a datacenter in Amsterdam, read this post to see how this was done!

Over the past few years I have been moving my data and work from local computers (mostly laptops) into the cloud. Cloud computing is done by servers in a datacenter, powerful computers that do the hard work. As my company grew, I needed more capacity. It was time to add some power to my cloud!

Fighting backscatter spam at server level

Configure Postfix to block spam before it enters the server

Sep. 10, 2019
Deal with backscatter spam by implementing a stringent SMTP delivery policy at MTA level.

This month I had to deal with backscatter spam, affecting one of the mail servers I manage. As server engineer I make sure that servers don't send spam and that incoming email gets filtered. Despite all good efforts, this server kept being blacklisted for sending spam to iCloud, Office 365 and Google Gmail for Business (G Suite). Read along to find out how what caused this and how to fix this.

Dig for dummies

Explaining an highly useful network tool

May 24, 2019
Learn how to use the dig command to query domain name servers to find the source of network problems, IP-addresses, hostnames, mail servers and related info.

When you're building websites, apps or email services you may run into domain names and their configurations. When everything is working as it should, most of this is invisible. But when troubleshooting a domain name configuration, it may be necessary to dig a little deeper... read along to learn how!

WordPress: 10 tips to secure your website

Keep hackers out of the world's most popular content management system

Mar. 31, 2019
A lot of people use WordPress to manage their website. Prevent your site from being hacked using this blog post.

A lot of people use WordPress to manage their website, therefore it's no surprise people ask me to have a look at their site's security. As ethical hacker, I encounter WordPress in different shapes, sizes and states. Some of them are really badly protected against hacks. Prevent your site from being hacked using these 10 practical tips.

Understanding the security concerns in shared hosting

Considering open ports and unused network facing services

Feb. 28, 2019
People pay me to hack them, provided I'll explain how I did it. Read along to learn how hackers use security holes to hack your app, webshop or website!

People pay me to hack them, provided I'll explain how it was done, so future hacks can be prevented. As security consultant, I scan for weaknesses in my clients' apps, webshops and websites. Very often a hack starts by exploiting a security hole that is visible remotely. Read along to learn how hackers find security holes and what you can do to secure them.

Is the Apple Watch the modern tool watch?

Testing the Apple Watch's usefulness in real life

Nov. 2, 2018
I tested the Apple Watch during my work in Frankfurt this week where I had to go inside an internet data centre.

This week I went to Frankfurt for business. I had to perform maintenance to servers in a data centre. This seemed like a great opportunity to test the Apple Watch's usefulness in real life (other than health and fitness). I wondered, is the Apple Watch the modern tool watch?

Optimising images for the web and performance

Reduce filesize with jpegoptim, optipng, pngcrush and pngquant

Sep. 26, 2018
Make your website faster by optimising the images. This posts explains how you can do this.

One way to make your website faster is to make it smaller. Not with tiny fonts, but with less bytes! More than half the weight of an average website is because of images. Yet very few people optimise their images for the web and performance, time to find out how much bytes you can safe!

Google Analytics vs AWStats

Understanding web traffic statistics software

Aug. 20, 2018
Comparing Google Analytics with AWStats to find out where they differ and which is better.

This month I have been working on website statistics, tracking traffic using different technologies. Some of my customers use Google Analytics, others use AWStats, and some use both. Which is better is often debated, but few people really understand the differences. Time to shed some light on the magic of web statistics.

Helping people with free software

Installing Debian GNU/Linux on an old laptop

July 20, 2018
This week I helped a man with repairing and reinstalling his computer with Debian GNU/Linux.

This week a man brought his laptop to the community centre where I help people with computer problems as volunteer. The old laptop wouldn't start anymore and had to be reinstalled. Instead of Windows, I installed a free operating system. I think it is important to tell you how and why I did it.

Cyber security: 5 easy tips to protect your server against hackers

Server hardening best practices for Windows and Linux

Mar. 10, 2018
These 5 practical cyber security measures will improve the safety of server, website and data.

This week one of my clients was hacked and asked me for emergency assistance to help secure their server infrastructure. It was a web server that ran WordPress websites on Apache (with PHP/MySQL), including a few webshops with customer data. This hack could easily have been prevented with the following best practices, is your server secure?

Clouds below my floor

Building a little datacenter in my basement

Aug. 31, 2017
Building a little datacenter in my basement utilising a very fast internet connection.

At my home I have this crazy fast optical internet connection. It is a 600MB up and down fibre connection which directly arrives in my home (no copper cables involved). It's like a private internet highway. Reason enough to find out if I could do something to make better use of all this speedy fiber galore...

The day I killed my LAN

Turned off my local network and went 4G only

July 31, 2017
I killed my office LAN and went 4G only. Saves a lot of clutter, energy and money.

Today I called my provider to quit my office's ADSL internet subscription, I don't need it anymore. I have turned off my local area network and switched my workflow onto mobile internet only. The simplicity and savings actually surprised me so much, that I made blog post for it.

iPad Pro as primary computer

testing iOS as primairy development platform

Aug. 15, 2016
Is the time right to use an iPad as primary development platform to get some real work done?

The lack of physical clutter, distracting branding, or blinking LED's makes the iPad Pro a textbook example of minimal design. My despiction of distraction explains my interest in using the iPad Pro as only computer to test if it is up to the task. Is Apple's latest effort on iOS enough to enable it to do serious development work?

Building the blog... in style!

Developing on a 20-year old computer with 16MB RAM and Windows 98

June 23, 2016
Find out if it is possible to turn a computer from the 90s into a modern development machine.

One must be a bit crazy to come up with the idea to build a blog (as in: actual programming) on an old 486 laptop with just 16MB RAM. I happen to be that crazy: I took my very first laptop from the 90s and decided to find out if it was possible to turn it into a development machine.

All blog posts
Contagious effect of an hacked website (red indicating trouble)
Contagious effect of an hacked website (red indicating trouble)
Digital technology and social change (by Martin Hilbert, University of California)
Digital technology and social change (by Martin Hilbert, University of California)
Server hardware inside a rack in the data centre
Server hardware inside a rack in the data centre
The world on your wrist - using Apple Maps in downtown Frankfurt
The world on your wrist - using Apple Maps in downtown Frankfurt
Implementing stringent SMTP restrictions in Postfix - annotated screenshot from main.cf
Implementing stringent SMTP restrictions in Postfix - annotated screenshot from main.cf
The error message was right, quite literally: the boot device is missing!
The error message was right, quite literally: the boot device is missing!
Averaging 3.4 milliseconds in pinging Google. That's fast, datacenter fast.
Averaging 3.4 milliseconds in pinging Google. That's fast, datacenter fast.
MacBook connected to the server in the datacenter through VMWare ESXi - installing GRUB boot loader on a virtual Debian GNU/Linux server
MacBook connected to the server in the datacenter through VMWare ESXi - installing GRUB boot loader on a virtual Debian GNU/Linux server
Typical slide on pace-cme.org
Typical slide on pace-cme.org
Keep in mind that help is available - I know my way around servers and cyber security
Keep in mind that help is available - I know my way around servers and cyber security
Using dig to get information about the SPF-records for a domain name, google.com
Using dig to get information about the SPF-records for a domain name, google.com
Bandwidth graph with unusual spike indicating that something is wrong - you don't need to be Sherlock Holmes to find it
Bandwidth graph with unusual spike indicating that something is wrong - you don't need to be Sherlock Holmes to find it
Feeling old already, my trustworthy old local area network (LAN)
Feeling old already, my trustworthy old local area network (LAN)
Once a hacker knows what software your website uses, its easy to lookup known security holes using databases like cvedetails.com
Once a hacker knows what software your website uses, its easy to lookup known security holes using databases like cvedetails.com
Charging and listening to music simultaniously using an Apple Lightning dock
Charging and listening to music simultaniously using an Apple Lightning dock
Leaking personal user information from the WordPress REST API
Leaking personal user information from the WordPress REST API
... apparently it needed a little encouragement from its modern cousins...
... apparently it needed a little encouragement from its modern cousins...
Bitmap images are like chessboards, where the pixels are squares
Bitmap images are like chessboards, where the pixels are squares

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