What I Learned Studying EKS Cluster Upgrades (Beyond Just "Click Upgrade")

I'm fairly new to SRE/DevOps, and one of the topics I recently spent time studying properly was EKS cluster upgrades . My first instinct, like most people starting out, was: "it's just a version bump, click upgrade in the console, done." That's basically what most beginner blog posts say too. But the more I read and the more I dug into real-world postmortems and discussions, the more I realized — the actual Kubernetes control plane upgrade is the easy part. Almost everything that can go wrong seems to happen around it, not because of it. Sharing what I learned here, mainly for my own notes, but hoping it's useful for anyone else early in their journey too. Learning #1: There's No "Undo" Button This was the first thing that surprised me. I assumed upgrades work like most software — if something breaks, you roll back. But with EKS, you cannot downgrade the control plane version once you upgrade it. So the plan can't be "upgrade, and if it breaks, revert." It has to be "test enough beforehand that breaking isn't really an option," and if something does go wrong, the fix is always moving forward, not backward. That single fact changes how you're supposed to approach the whole thing — testing has to happen before the button is clicked, not after. Learning #2: APIs Get Deprecated, and It's Usually Not Your Own Code That Breaks Kubernetes removes old API versions on a schedule. I already knew this conceptually, but what I didn't realize is that the risk usually isn't your own YAML files — it's the Helm charts and third-party tools you installed a while back and forgot about , which might still be using an older API version internally. There are tools built exactly for catching this before it becomes a problem: pluto detect-helm -owide pluto detect-files -d ./manifests kubent (kube-no-trouble) does something similar. I hadn't heard of either tool before researching this, and it made me realize how much of "being good at Kubernetes" is really just knowing which small tools e