Bare-metal Kubernetes, Part VIII: Containerizing our Work Environment

Setting up Kubernetes once is not that hard to get right. Where things usually start to go wrong is when the cluster is left to its own devices for extended periods of time.

All of a sudden you're dealing with certificates expiring rendering your nodes unreachable, and your workstation's package manager has dutifully updated all your cli tools to new versions causing subtle, or even not-so-sublte, incompatibilities with the cluster or your workloads.

To get out ahead of some of these issues, and to get a good overview of the sprawling ecosystem of tools we're using at the moment, I've decided to compile all of them into a singular docker image, which can be upgraded as we go.

Series Index

Complete source code for the live cluster is available @github/MathiasPius/kronform

Picking a Base

I used to be a bit of an Alpine Linux fanatic. I still am, but I used to too. I have however mellowed out a bit, and the trauma of dealing with all manner of OpenSSL, musl, and DNS-related issues over the years, has meant that lately I've been reaching for debian's slim container image whenever I've needed something to just work.

Theoretically debian:bookworm-slim's 74MB image size means that it's an order of magnitude larger than alpine:latest's meagre 7.33MB, but 74MB is still nothing, and if you're diligent about pinning & pruning, that 74MB is stored exactly once, so who cares?!

FROM debian:bookworm-slim AS installer

Structuring our Stages

Luckily for us, most of the tools we use are available as static binaries, which means we don't have to deal with convoluted installation processes, and instead can just download the file and be on our way. For this, we'll still need at least one tool: curl (and also ca-certificates so we can use https)

RUN apt-get update \
    && apt-get -y install --no-install-recommends ca-certificates curl \
    && apt-get clean

We'll need somewhere to put the files. We could install them directly into /usr/local/bin for example, but we don't really need curl in our final image, so instead of trying to uninstall the package once we're done, we'll just rewind the clock and use an entirely separate stage!

This way we can just copy over our downloaded files from our installer stage, and leave curl behind.

The advantage of this is that tools we add in the future might not be so simple to install, or may even require building from source! In that case, we can clutter up the installer stage with toolchains, makefiles, libraries, and what have you, and still be able to build a small and shippable final image, without all the cruft.

Just to make copying from one stage to another easier down the road, we'll put all the binaries in a single directory: /tools:

RUN mkdir /tools
WORKDIR /tools

Collecting Binaries

With most of the prep done, it's time to actually get some tools. Let's start with kubectl an absolute necessity for any Kubernetes administrator.

Checking the current version of our Kubernetes cluster shows that we're on v1.27.4:

[mpd@ish] $ kubectl version --short
Client Version: v1.27.4
Kustomize Version: v5.0.1
Server Version: v1.27.4

The kubectl binary can be downloaded directly from

But of course we won't be staying on that version for long. 1.27.5 and 1.28.1 has just been released, so we will likely be migrating sooner rather than later. To make this easier, and to make it very easy to see which version of each is included from the Dockerfile alone, we'll use ARGs to define the version:


RUN curl -L -o kubectl${KUBECTL_VERSION}/bin/linux/amd64/kubectl \
    && chmod u+x kubectl

Here we're downloading the binary directly, and marking it as executable for the owner. For other tools (such as flux), we'll have to extract the binary from a tar.gz archive:


RUN curl -L -o flux.tar.gz${FLUX_VERSION}/flux_${FLUX_VERSION}_linux_amd64.tar.gz \
    && tar -xf flux.tar.gz \
    && rm flux.tar.gz \
    && chmod u+x flux

We repeat the above procedure for talosctl, yq, sops.

Workspace Stage

With all our binaries rolled up into a nice little docker image, we can start configuring a separate stage which will be the one we will actually reach for, whenever we need to interact with the cluster.

Once again, we start from debian slim

FROM debian:bookworm-slim AS workspace

Running as root is of course considered haram. Perhaps more importantly, our repository will be cloned onto our workstation itself and then mounted into the running container, which means that the files will, nine times out of ten, be owned by our the default UID 1000. If we used a root container, any files we created inside the container would automatically be owned by root, meaning if we exported a yaml manifest or kubectl cp (copied) a file from a container onto disk while inside our container, we would have to elevate privileged to access it outside of the container. Apart from the the security implications, this is just plain tedious!

We'll configure a user with the clever name user inside the container with UID and GID 1000. That way the owner id will be identical inside and outside of the container, and we can transition ourselves and files seamlessly between them.

ARG UID=1000
ARG GID=1000

RUN groupadd -g ${GID} user
RUN useradd -M -s /bin/bash -u ${UID} -g ${GID} user

Once again we're using ARG, so we can set it once (and change it, if I/you/we happen to be 1001 for example) and reuse the ID in the directives to follow.

As mentioned, we'll be mounting the repository inside the container, so we'll need a directory. I've chosen /data for no particular reason.

RUN mkdir /data && chown user:user /data

Next, copy the binaries over from our installer stage and set the owner:

COPY --chown=user:user --from=installer /tools/* /usr/local/bin/

Finally, assume the identity of this mysterious user when we docker run the container:


Keys to the Kingdom

Now, since we're using SOPS with GPG to manage secrets in our repository, we'll need to install GPG inside the container, as well as a text editor of some sort in case we want to ever make changes while inside.


RUN apt-get update \
    && apt-get -y install --no-install-recommends gpg $EDITOR \
    && apt-get clean

We'll get two birds stoned at once here by defining the EDITOR environment variable while we're at it. This way when we want to edit encrypted files inside of our container using sops myfile.yaml, it'll default to using our selected editor. Neat!

Entering the Workspace

With our Dockerfile (final version available here) setup, it's time to build and see if everything works as intended.

[mpd@ish]$ docker build -t tools:latest tools/

The Dockerfile we've been writing is located at tools/Dockerfile

No big surprises, but we need to do some thinking when running the container.

First of all we'll need our repository code available. At least in its encrypted form:

[mpd@ish]$ docker run -it --rm -v $(pwd):/data tools:latest

Okay, that part didn't require much thinking, but this next part will: We'll need some way of accessing our GPG keys inside of the container. By far the easiest way to do this, is to mount our own $HOME/.gnupg directory inside the container, and then less intuitively, mounting /run/user/$UID as well. This will make the gnupg agent's unix sockets available to the sops/gpg inside the container, effectively exposing the gpg environment from our workstation.

Of course /run/user/$UID contains a lot more than just GPG sockets, so it would of course be to be able to just mount /run/user/$UID/gnupg and limit the exposure, but quite frankly... I can't figure out how to make this work.

I initially tried mounting just /run/user/$UID/gnupg which intuitively should work, but sops throws back a GPG-related error alluding to /home/user/.gnupg/secring.gpg not existing, which is fair... Except that clearly appears to be some kind of error of last resort, since mounting the entire /run/user/$UID directory does work, yet produces no secring.gpg file.

I won't go as far as to endorse mounting the whole directory, but the container we're mounting this directory into is about as lean as they come. There's a bare minimum of packages, and a handful of binaries. The odds of a vulnerability existing in software which is able to leverage this directory mount into some kind exploit is limited, even in the scope of our workstation.

The risk of it happening within our barebones container? Astronomical.

docker run -it --rm                       \
    -v $(pwd):/data                       \
    -v /run/user/1000/:/run/user/1000/:ro \
    -v $HOME/.gnupg:/home/user/.gnupg:ro  \

A bit of a mouthful. At this stage I'd suggest either throwing this blurb into a script file so you don't have to wear out your up-arrow key

Incorporating our Credentials

Up until now I've of course been using the kubectl and talosctl binaries installed on my host operating system, which meant installing our kubeconfig and talosconfig files in my local home directory so they could find them. Since everything is moving into the container now, those credential files have to move too.

The obvious thing to do, is to just mount the ~/.kube and ~/.talos directories directly, but this exposes all our Talos/Kubernetes clusters to the container, not just the one we're operating on, and we have to mount multiple directories.

Since talosconfig and kubeconfig already exist in an encrypted state in the repository, and we now have gpg & sops configured within the container, a much cleaner approach would be to simply decrypt on the fly and install ephemeral kube and talos configuration files inside the container.

This is easily achievable, by overriding the default bash entrypoint of the debian bookworm image.

First, create our decryption script tools/

#!/usr/bin/env bash

mkdir /home/user/.talos
sops -d --input-type=yaml --output-type=yaml talosconfig > /home/user/.talos/config

mkdir /home/user/.kube
sops -d --input-type=yaml --output-type=yaml kubeconfig > /home/user/.kube/config

# Start the shell

In all its simplicity, the script just decrypts and installs our configs, then hands over the reigns to bash. Sops can work with arbitrary data, so the --input-type and --output-type options are necessary, to let it now that the passed in files aren't fully encrypted, but actually just contain partially encrypted yaml. Usually sops is smart enough to figure this out on its own, but since there's no yaml extension on either of the files it needs a little help.

Next, we need to obviously copy this script into the container image, and instruct Docker to execute it as the first thing:

COPY --chown=user:user --chmod=0700 /usr/bin/local/entrypoint
ENTRYPOINT ["/usr/bin/local/entrypoint"]

Now we won't even need to keep our credentials around on our machines. Sweet!

Painless Updating

With all that in place, let's take our container for a spin!

The latest version of Talos is 1.5.1, putting us a couple of versions behind, and ditto for Kubernetes. Let's start with Talos.

Upgrading Talos

Luckily upgrading from 1.4.7 to 1.5.1 requires no special attention or at least none that affect us, however the only supported upgrade path by Talos between minor versions is from latest patch to latest patch. This means that in order to arrive at 1.5.1, we have to take a detour to 1.4.8, requiring a two-phase upgrade of 1.4.7 -> 1.4.8 -> 1.5.1

Let's get to it!

We start by upgrading the version of talos installed in our container to the version we want to run. This isn't strictly necessary to do at this point, since the talosctl upgrade command simply takes an container image and doesn't much care if the version we're installing is behind or ahead, but by upgrading our local version first the default image to upgrade to will automatically be our target version, meaning we won't accidentally fat-finger the procedure and initiate a rollback.

Change the version in our Dockerfile:


Once rebuilt, we enter our container. I've written a justfile for making it a little easier for myself. If you're not familiar with Just, you should be able to glean what's going on from the link.

[mpd@ish] $ just tools
docker run -it --rm                         \
    -v $(pwd):/data                         \
    -v /run/user/1000/:/run/user/1000/:ro   \
    -v $HOME/.gnupg:/home/user/.gnupg:ro    \
user@104e7ee67743:/data$ # And we're in!

Presented with our very anonymous "user" terminal, we'll kick off the upgrade procedure. Taking care to include the --preserve option, so as to not repeat the massive blunder that was The First Incident.

user@104e7ee67743:/data$ talosctl -n upgrade --preserve

We don't have to include the --image option here, since it defaults to the version of our talosctl, which is already 1.4.8

Talos does its thing, cordoning the node, upgrading Talos and booting into its upgraded version.

Let's see if everything is working as intended. Listing all our nodes, shows that the one node has indeed been upgraded:

user@104e7ee67743:/data$ kubectl get nodes -o wide
n1     Ready    v1.27.4   Talos (v1.4.8)   6.1.44-talos # <-- this one
n2     Ready    v1.27.4    Talos (v1.4.7)   6.1.41-talos
n3     Ready    v1.27.4      Talos (v1.4.7)   6.1.41-talos

Out of an abundance of caution, I also quickly log into the Ceph dashboard to check that all OSDs have recovered.

Next, we upgrade the remaining two nodes. Making sure that the cluster is healthy between each upgrade.

user@104e7ee67743:/data$ kubectl get nodes -o wide
n1     Ready    v1.27.4   Talos (v1.4.8)   6.1.44-talos
n2     Ready    v1.27.4    Talos (v1.4.8)   6.1.44-talos
n3     Ready    v1.27.4      Talos (v1.4.8)   6.1.44-talos

So far so good! Now at 1.4.8 across the board and no worse for wear we repeat the procedure, but this time wth 1.5.1:


And yadda, yadda, yadda...

user@e2029f39cf11:/data$ kubectl get nodes -o wide
n1     Ready    v1.27.4   Talos (v1.5.1)   6.1.46-talos
n2     Ready    v1.27.4    Talos (v1.5.1)   6.1.46-talos
n3     Ready    v1.27.4      Talos (v1.5.1)   6.1.46-talos

We're on 1.5.1! At this point I manually edited the machineconfigs of each Talos node to 1.5.1, just so they wouldn't have to start from scratch at the the initial 1.4.6 in case of a potential rebuild in the future.

Next up, Kubernetes!

Upgrading Kubernetes

Before upgrading Kubernetes, even between minor versions, you should always check out the list of deprecations and changes, to see if it might interfere with any of your workloads!

As it turns out, the version of Cilium we're running (1.13.6) doesn't even support Kubernetes 1.28, nor does even the latest stable version! Kubernetes 1.28 support is only available in Cilium 1.15 which is a pre-release version, so we'll have to settle for 1.27.5 for now.

No matter, a patch upgrade is still an upgrade.

Since talosctl will be doing the upgrading for us and we've already updated it, we're technically already set, but like before it'd be great to be able to interact with the cluster directly after the upgrade from within the container with a known-compatible client, so let's upgrade kubectl right away:


We rebuild the container once again and jump into it. This time we have to specify the target version, since talos 1.5.1 by default assumes 1.28.0 is desired. We also do a dry run just as an extra precaution:

user@5fe767daf694:/data$ talosctl -n upgrade-k8s --dry-run --to 1.27.5

Satisfied that this won't unleash hell on earth, we snip the --dry-run and go again:

user@5fe767daf694:/data$ talosctl -n upgrade-k8s --to 1.27.5

Although we're explicitly selecting node here, the upgrade-k8s command will automatically upgrade the entire cluster, one piece at a time.

Once complete, make sure everything is in order:

user@5fe767daf694:/data$ kubectl get nodes -o wide
n1     Ready    v1.27.5   Talos (v1.5.1)   6.1.46-talos
n2     Ready    v1.27.5    Talos (v1.5.1)   6.1.46-talos
n3     Ready    v1.27.5      Talos (v1.5.1)   6.1.46-talos

v1.27.5 across the board, and all nodes ready. Looking good!

Finally, we update our local copies of the machineconfigs for our nodes, in case we need to recreate them, using the handy machineconfigs/ script, and commit the new ones to git.


This post went on a little longer than originally intended, but ended up providing (I would say) a good explanation of not only how to containerize a Kubernetes-related work environment, but also a pretty decent demonstration of why, as exemplified by the extremely short section dedicated to the upgrade procedure.

This post was initially inspired by a reader who ran into problems following a previous post, because I had completely failed to document which version of each of the tools I was using, and not knowing there were multiple wildly different yq.

If nothing else, this post and the accompanying code changes in the GitHub repository, should provide a definitive reference, for anyone else trying to follow along at home :)