Harvest Java Heap Dumps in constrained environments

Creating and analyzing Heap Dumps is a standard for analyzing memory issues with JVM based programs. To do this, you have to: create the Heap Dump (duh!) move the data to your computer actually analyze the data Each of these steps has it's own challenges though the first two seem trivial at first sight. Creating the Heap Dump The main challenge in Heap Dump creation I faced in today's production environments is that only essential software is installed in order to keep containers and the potential attack surface small. [Read More]
java  jvm  heap  gc 

Fixing the problem of too many tabs

Tab mayhem and windows inflation How many browser tabs are open on your browser right now? Too many to count? Let me guess: Rows and rows of tabs belonging to different research tasks that you want to pick up later. The occasional tab on social network. That store you still have a cart open with that thing you maybe want to buy. Some are still relevant but many are not. [Read More]

Why does MaxRAMPercentage stop working at heaps of ~ 30 GB?

The other day at work a Clojure program on a machine with 100 GB ran into OutOfMemory errors. A quick look at the metrics showed that the heap was only at about 30 GB though. Checking the JVM flags I found a configuration that is commonplace: -XX:MaxRAMPercentage=80 So one would assume that the JVM could have sized the heap much larger than it actually did. Thanks to docker this behavior can be observed quite easily by doing a few tests like this one: [Read More]
jvm  heap  memory 

Create downtimes with Instance Refresh for EC2 Auto Scaling

When AWS launched Instance Refresh for EC2 Auto Scaling last year my colleagues and me were delighted: Should we be able to retire our half baked and mostly working lambda for restarting ec2 instances and hand this over to AWS Auto Scaling? I think we were not the only ones looking forward to this: Auto Scaling groups is an extremely popular option of the most popular AWS service (EC2) of the biggest cloud provider in the world. [Read More]
aws  ec2 

Do you ever forget to push your git commits?

The title of this post is a rhetorical question. At least I think it is. Or I like to think it is. What I can say with certainty is that I forgot my fair share of pushes. 😅 Sometimes I was the one tripping over my own mistake (Why is that commit not live? Ah, because the pipeline did not run. Because I did not push. facepalm). Sometimes my colleagues had to find out. [Read More]
git  linux 

Notifications for failed cron jobs

Every few years when I setup a new computer I stumble over the same question: "How do I get notified of failed cron jobs again?". It is pretty simple, but as I tripped over it again today, here is a little write-up so I do not have to google this again. Or potentially I will and then hopefully this post will turn up in the search results.😉 As cron is an old program from the days where the server use case was the predominant one, it will send emails with the output it's jobs will produce. [Read More]
cron  linux 

Create virtualenvs in project directories

It's quite handy to create the virtual environment aka venv for a python project in the project folder itself. This means: No huge .virtualenvs folder in your home directory with a lot of envs which you will never use again (The one on this computer is 1.2 GB big although I do not work with many Python projects at all(!)). If you are done with a project and delete all local files, the corresponding environment will be gone with it. [Read More]

Why does poetry not use the specified Python version?

TL;DR: There is only one way to install poetry proper and that is with the installer script provided by the project itself. I was sweating for the better part of an afternoon with a colleague about this. I had installed poetry, the new star in the python tooling world and it kept using the global version of Python instead the one for the project at hand, though poetry's own pyproject. [Read More]

Missing system modules in Python

I got to work on a Python code-base in the last days and have been struggling to get to a stable development environment. I learned some lessons along the way. Here is one of them, as it seems to be rather common and causes headaches for many people (a simple search has a whopping half a million hits on Google). The error ModuleNotFoundError: No module named '_lzma' [Read More]