Simon Krenger

Due to COVID-19, like many others I am currently working from home and as a result I took the chance to update my home office. Working with a small laptop screen for months is not optimal, so I went the ultrawide route and got myself a Dell U3818DW monitor.

Since I did not find a lot of information about running this monitor with Linux, here is a quick overview. To summarize, everything works out-of-the-box.

With OpenShift 4, Red Hat introduced Red Hat Enterprise Linux CoreOS. It is a very minimalistic operating system, focused on running container workload.

This new minimalism comes with some challenges. There are no more RPM packages and most of the tools we know and love are missing! Luckily, there is the Red Hat supplied toolbox container that contains all the necessary tools and is nicely integrated.

So to start the toolbox, use oc debug node/<nodename>. This will start a privileged container on the node you specify, mount the host filesystem on /host and drop you into a shell:

$ oc debug node/worker-0.lab.openshift.krenger.ch
Starting pod/worker-0labopenshiftkrengerch-debug ...
To use host binaries, run `chroot /host`
If you don't see a command prompt, try pressing enter.
sh-4.2# chroot /host
sh-4.4# toolbox
Container started successfully. To exit, type 'exit'.
sh-4.2#

Now we are running in the toolbox container on our CoreOS host with all the tools we know at our disposal, for example sosreport:

sh-4.2# sosreport

Running sosreport will generate a sosreport in /host/var/tmp/, which means it will be accessible in /var/tmp/ on the CoreOS host itself.

For OpenShift 4, the upgrade paths are kept in the cincinnati-graph-data repository as YAML files and then exposed via an API.

There is a Red Hat Solution describing how this data can be queried via api.openshift.com and how you can use this data in your automation:

$ curl -sH 'Accept:application/json' 'https://api.openshift.com/api/upgrades_info/v1/graph?channel=fast-4.2&arch=amd64' | jq .

While this data is quite helpful for automation (the Solution also describes helpful queries), it is not very nice to look at the raw data. If you are looking for a graphical presentation of that data, you should check out this wonderful website that is maintained by a Red Hat colleague with hourly generated data: www.ocp-upgrade.net

So here is another one from the trenches.

More than once one of our OpenShift Container Platform customers approached us and said something along the lines of: “Help, I cannot see the X-Forwarded-For header in my application, our OpenShift Router is probably configured incorrectly!”.

In such cases, it is often a good idea to check what is really being forwarded to the Pods in the cluster. For this, I typically use my simonkrenger/echoenv container to print the headers received by the application. In many cases, it turns out that the application affected is a Spring Boot application and the header is passed correctly to the Pod itself. But the Spring Boot application does not show the header anyway.

We have observed a behaviour of Spring Boot that leads to the X-Forwarded-For header not being passed to the application, as it is consumed by Spring Boot. In the application.properties of a Spring Boot application, the following setting controls this:

server.use-forward-headers: true

This configuration leads to the header being consumed by Spring Boot and the header not being available in the application. See also the relevant sections in Spring documentation. Good to know.

Kubernetes uses etcd as the persistent store for API data. As etcd is a distributed key-value store, we can also use command line tools to query this store. The examples in this post are for OpenShift 3.x.

Apart from just using get, there is also the possibility to perform the following actions on certain keys:

• put to write to a key – unless you know what you are doing, don’t touch the Kubernetes data in etcd, as this will manifest in very strange Kubernetes behaviour.
• del to delete a key – also, this may break your Kubernetes cluster by introducing inconsistencies.
• watch to keep a watch on an object. This is very helpful to track changes on a certain object.

The get action is probably the most helpful functionality for in-depth API debugging directly within etcd.

Tanuki has released a new version of their wrapper today (this has to be some kind of speed record for the new release here!). In this post, I provide the compiled version 3.5.43 of the Java Service Wrapper for Windows x64.

Working for Red Hat certainly has its perks. One of them being that I have access to all the content from Red Hat University and I am able to take Red Hat exams for free. With these perks come of course some expectations. Customers expect a Red Hat TAM to be knowledgeable on a wide range of Red Hat products, even if they are not directly related to the function of the TAM.

The most common certifications for System Administrators and also for new TAMs are the Red Hat Certified System Administrator (RHCSA) and the Red Hat Certified Engineer (RHCE). So after passing my RHCSA exam in December 2019, I passed the exam EX294V8 to become a Red Hat Certified Engineer (RHCE) in mid-February. The next step is obviously to become a Red Hat Certified Architect (RHCA), in my case focussed on Cloud technologies such as OpenShift and Containerisation.

To prepare for the RHCE, I used Red Hat University Online courses (RH294) and also prepared using Tomas Nevars Ansible Sample Exam. As others have already noted, the RHCE for RHEL8 is a pure Ansible exam, so knowing your Ansible playbooks in and out will help you with the exam. The above courses and sample exam are great preparations for the exam itself.

For editing YAML, be it for OpenShift / Kubernetes or Ansible, having your editor set up right can help to avoid common mistakes. So here is the minimalistic config in my ~/.vimrc to make working with YAML files easier. I am sure there are even more plugins or settings available, but this minimal set of commands works fine for me:

set ts=2
set sts=2
set sw=2
set expandtab

syntax on
filetype indent plugin on

set ruler

Tanuki has released a new version of their wrapper in late January. In this post, I provide version 3.5.42 of the Java Service Wrapper for Windows x64.

As always, I don’t guarantee anything, so please note:

Some time ago, I had a curious case of very slow DNS resolution in a container on OpenShift. The symptoms were as follows:

• In the PHP application in the container, DNS resolution was very slow with a 5 second delay before the lookup was resolved
• In the container itself, DNS resolution for curl was very slow, with a 5 second timeout before the lookup was resolved
• However, using dig in the container itself, DNS resolution was instant
• Also, on the worker node, the DNS resolution was instant (using both dig and curl)

TL;DR: Since glibc 2.10, glibc performs IPv4 and IPv6 lookups in parallel. When IPv6 fails, there is a 5 second timeout in many cases before the lookup is returned. Disable IPv6 DNS lookups by setting “single-request” in “resolv.conf” or disable the IPv6 stack completely.