This post is born out of a real-world experience. While deploying a CoreDNS dashboard in Grafana to monitor OpenShift DNS servers, I discovered several quirks that not only impact performance but also explain some puzzling application behaviors driven by Java’s DNS implementation. Let’s dive in. DNS Service Discovery in Kubernetes To understand the basics of what is DNS and his invention, I recommend an interview with Paul Mockapetris. This post focuses on how it is implemented in Kubernetes/OpenShift and how Java resolution interacts.

This article shows how to use a private ipa-server to provide certificates to kubernetes applications. There is a very good post on the subject about how to configure Identity Manager (ipa-server in RHEL) by Josep Font. A developer subscription for RHEL at no cost can be used, or CentOS Stream can be used for playing with the latest ipa-server version. Another really good post about Cert-manager integration is done by another two colleagues, Jose Angel de Bustos and Jorge Tudela.

After several years working in the container space, I still hear in a lot of sessions and meetings that Kubernetes is not meant for running stateful applications. Of course, stateless apps are a lot more easier, less challenging and disposable than stateful apps. But in the end, almost every useful application depends on data. Kubernetes is a great choice to scale up/down apps and adapt them to demand, but if a database/broker/other-stateful-app cannot scale similarly, we can guess where the bottleneck and the limits would be.