Lessons learned in 2016

by Jannik Arndt


Do not fix your code.

Rather understand why nothing kept you from creating this bug. Make your code so easy that this bug would have been obvious the first time.


Automate early.

You know, CI/CD. Or just clean-up-scripts. Or a complete infrastructure-as-code. Remember: A script to setup something is the best documentation!


A function must not do more than one thing.

If a function name contains “and” there’s still work to do. Build small pieces.


Side effects are the root of all evil.

If you need side effects (like database or file outputs), let it be the only thing a function does.


It’s all about data.

Business logic is just a concept to change data.


A system is defined by its input and output.

Every description of anything should focus on these two things first.


I was quite surprised at how difficult it is to get absolutely razor sharp images out of a very good (high-end-consumer/semi-pro) DSLR camera, namely the Nikon D7100. So I made the test: What settings in terms of aperture, shutter speed and ISO yield the sharpest landscape image?

If you write Scala in a Java-centric environment, chances are you might wind up with a Maven project, defined in a pom.xml. While this can work, it brings a few extra caveats if you want to submit your project to Maven Central (aka Sonatype OSSRH). Step 1: Claim your Group ID When you first publish something to the Sonatype OSSRH, you have to create a JIRA account and then create a ticket for a new project.

Storing case classes in a MongoDB database is incredibly easy, once you know how. The same goes for java.time classes such as ZonedDateTime, LocalDate or Duration.

This example uses the official Mongo Scala Driver in version 2.x and the bsoncodec project by Ralph Schaer.

This post contains the absolut essence from the Terraform Getting Started Guide: https://www.terraform.io/intro/getting-started/install.html

Ever wondered where bad code comes from?

“This story is done”

“Shouldn’t someone review it first?”

“Oh, yeah … erm … I’ll do a quick refactoring first and then…”

…when that other person is on holiday!

Some ideas seem great at first but turn out to be incredibly bad in hindsight. I reviewed such an idea today.

I tried to create a single image that contains all the most important git commands:

The Problem

You’re a corporation. Your IT department is old, slow and can’t innovate. Your competitor however can. So you try what every corporation tries: Two-speed IT.

Last week one of our programs failed looking up an airplane by its registration. That’s not a surprise, since ac regs are a horrible identifier. They change all the time. Also there is almost no naming rule at all. Wikipedia states

When painted on the fuselage, the prefix and suffix are usually separated by a dash (for example, YR-BMA). When entered in a flight plan, the dash is omitted (for example, YRBMA). In some countries that use a number suffix rather than letters, like the United States (N), South Korea (HL), and Japan (JA), the prefix and suffix are connected without a dash.

My favourite animal: The Beluga!

TL;DR: You don’t. We eventually gave up on it.

My personal lessons-learned:

  • Pentaho Kettle (or “Community Edition”, CE, i.e. the open-source core) is a great product for one-time data transfer or on-demand data transfer, but not for resilient, scheduled jobs.
  • The “Enterprise Edition” (EE) adds scheduling that doesn’t work reliably, and a very powerless server.
  • Kerberos is a bitch.


You have a denormalized table and want to extract a column into a dimension table.


You have to keep the ids.


You use an Oracle database.

I cannot believe that googleing “talend does not work” does not find anything helpful. With this entry I try to fill that void in the internet.


Do not fix your code.

Rather understand why nothing kept you from creating this bug. Make your code so easy that this bug would have been obvious the first time.

Being the IT-guy aka personal first-level-support™ for way more people than I am comfortable with, I have held quite a few mobile phones in my hand and stared into the abyss that is their home screen. The home screen is the modern view into someone’s soul. In a post-privacy-world it is probably one of the most private things we have, since it is utterly worthless to someone who does not interact with it on an hourly basis and has grown to live with whatever way the apps are scattered around the screen.

(via I Love Programming)

Thank goodness, we don’t do production.

Since I bought my personal domain name around 2003, I went through several web-solutions, using static html pages, php pages, a custom designed php cms, finally Wordpress and now, as of yesterday, I am back to static html. The 2016-flavour however, which is another attempt of separation of presentation and content (a concept I highly endorse as a LaTeX user).