Upgrading k8s cluster to 1.13.6

Upgrading k8s cluster to 1.13.6

Since I last posted, I’ve been focusing almost all of my “fun coding” time on contributing to the Kubernetes code base. You can see my contributions on my Github. I’ve been particularly focusing on the components of the code base owned by sig/node. It’s been rewarding and a great learning experience… but it does mean I haven’t been focusing on adding features to my personal Kubernetes cluster. And since that’s what I mainly blogged about, it also means I’ve been blogging less. While I hope to blog more about my k8s contributions in the future, I currently feel I should be 100% focused on writing and reviewing code.

However, while I’m not actively developing on my Kubernetes cluster, I still need to ensure I’m using a supported version without any known security issues. In this blog post, I outlined my schedule for upgrading my cluster and also promised to blog about the process. So I’m back posting :)

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In this blog post, I’ll talk about my experience upgrading my Kubernetes cluster from 1.12.7 to 1.13.6.

Upgrade schedule

In the aforementioned previous blog post, we outlined our cluster upgrade policy as the following:

If there is a patch release to address a security vulnerability, we will apply it immediately… Otherwise, we will check at the start of each month for if there is a new patch release for our minor version, and will apply it if so. On a quarterly cadence, we will check if there is a new minor version release, and update if necessary to ensure we are using one of the three latest minor versions.

Currently, our cluster is running 1.12.7. Recently, k8s announced CVE-2019-11246, which impacts all 1.12.x clusters below 1.12.9. So we need to upgrade to at least 1.12.9.

However, with release of of k8s 1.15 this week, 1.12 is moving out of support window (i.e. 1.12.10 will be the last patch release). As a result, we decided to upgrade to 1.13.x. We need to upgrade to 1.13.6 to get the fix for the previously mentioned CVE.

As a reminder, because we use kops to manage our cluster, Kops support for different minor versions dictates which minor versions we can use. Kops 1.13 is in beta, and I feel comfortable using it to deploy our cluster. However, Kops 1.14 is still in alpha, so I’m not yet comfortable using it, and thus we’re blocked from upgrading all the way to 1.14.x. So 1.13.6 it is!

Upgrade experience

Overall, the upgrade experience was smooth! At this point, the 1.13.x release has been out for a long time and is pretty stable. Furthermore, the new functionality added in 1.13 does not have a substantial impact on the applications running on our cluster nor on the way we manage our cluster.

In the past when we ran kops rolling-upgrade, we’ve had issues with stale DNS records causing workers to try and contact the old master instead of the new master. To address these issues, we doubled both the timeouts we wait after terminating a machine and the amount of time we allow kops to attempt verification. This migration did not experience DNS staleness issues, although we can’t be positive it was because of the increased timeouts and not a kops bugfix.

Overall, a smooth migration!

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Future plans

While I don’t have any concrete plans, I’m thinking about no longer using Kops to deploy my cluster, and instead using Kubeadm and Packer/Terraform to build/deploy machines. My work with sig/node has lead to the desire for less abstractions between the k8s cluster and myself. Also, if I was using kubeadm, I’d be able to use newer versions of k8s, without needing to wait for the accompanying kops release, which typically lags a minor version or two behind. Like I said, I have no concrete plans, but I’m thinking about it. If I do decide to make this change, I will certainly blog about it :)

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