An Inescapable Hell of Networking

Sep 23, 2022, by Ryan Heywood

Note: The choices I've made are my own and are solely due to how I want to learn more about the involved technology. Kubernetes is not the "answer to everything", but it is the answer to "what do I think would be fun to learn?". The most important thing, is that it WAS fun to learn. I enjoy learning, and I enjoyed learning all the information that I'm going to talk about in this article. In addition, the points that I make in this article are absolutely not a reason to ever attack someone personally, and even though I disagree with the decisions made, it is never right to contact those people with harmful intent.

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If you've interacted with the Cloud Native Computing Foundation, you may be familiar with the CNCF Landscape. Beware - opening that link might crash your computer because of how many assets it has to load. Most of these projects have something to do with Kubernetes, container orchestration, and almost all of them in some way interact with what we call Amazon's computers "The Cloud™". The fundamental design of The Cloud™ is that you can run things on someone else's computer, therefore you aren't responsible for when the computer goes offline. This is excellent, as you can typically pick and choose your provider based on how likely it is their infrastructure is going to catch on fire compared to yours.

However, this leads to what is (technically!) the source of many issues in modern day technology: computers need to be able to talk to each other. To do so, they need to involve components such as switches, routers, NATs, and more. For a specific infrastructure setup (Kubernetes), this involves a component called the Container Network Interface. It is a standardized interface for programs that run alongside your cluster, configure routes to and from your containers, and (most critically for this article) can be used to configure a NetworkPolicy resource type. Additionally, because it is an interface, it can be replaced with any component I choose to use. Therefore, we'll evaluate and determine which of Flannel, Cilium, and Calico are ideal for setting up networking.

A NetworkPolicy is a resource type in Kubernetes that can configure in OSI Layer 3 (i.e. IP & Port) whether or not a resource can connect to another resource. Therefore, it's the responsibility of the network routing component (the CNI) to decide whether or not the resource can perform that connection. Unfortunately, Flannel, one of the aforementioned CNI candidates, does not support NetworkPolicy resource types. Because of that, it is no longer a valid candidate for the Kubernetes cluster, and we have begun our descent, entering the first level of hell.

That leaves us with two options, Cilium and Calico. The cloud provider that I'm currently using, DigitalOcean, has a managed Kubernetes infrastructure which came with Cilium preconfigured. This made it an ideal candidate for when I wanted to test out CNIs in my new cluster. I tried deploying Cilium to the cluster, but I was unable to get it working. Even after going to a DigitalOcean managed cluster and pulling the config directly from there, I was no better off, and we have plunged further, into the second level of hell. After that, Calico seemed like our last chance and potential savior.

Since we're now left with Calico, I think it's a good time for a story. Over a year before publishing this post, I was working with a company called Beeper. I was there to help move their old Kubernetes setup (managed by Kubesail) to a self-managed cluster on Hetzner. This was actually my first time setting up a Kubernetes cluster from scratch, so I had to make the incredibly important decision of choosing a CNI out of the gate. I decided to go with Calico because it looked like it was the easiest to deploy. It went almost seamlessly and I was able to deploy it with Wireguard integration, which means traffic was encrypted (and therefore private and secure) between nodes.

Since then, Calico seems to have moved to a new form of deployment. While previously it was possible to just grab a manifest and throw it into a new cluster, the system they use now is incredibly complicated. In fact, during my first attempt at deploying Calico, I was unable to get it to successfully deploy the fundamental resource it needs to run because the size of the file was too large. After I was able to fix that issue (I used kubectl --server-side=true), I was able to deploy the Installation resource and set up the CNI, but a while after that, I was Spartan-kicked into the third level of hell as the Installation appeared to have deleted itself and the network became unavailable.

When I found this out, I was in a meeting with some friends, while I hoped to get some work done. On Thursdays, some of the Hashbang community joins a video call as we talk about some things that have happened in the past week, and I've recently taken to doing some work while talking with my friends. This is helpful as sometimes they can help me debug things, and in return sometimes I will help them debug things. The first thing I did that Thursday after joining the call was to pull up k9s and check out my nodes, only to see they were reporting the NetworkUnavailable status. I checked the Typha (Calico) Operator and noticed that it had lost the Installation resource, which meant it could no longer deploy resources to the cluster. At this point, I decided I would try to find a way to work around the Installation resource. Still on the call, I was able to talk with a friend who was also running Calico in one of his clusters, who mentioned that he had used the Helm templates as an alternative to deploying the CNI. This seemed like a good plan and, given I didn't want to be stuck in hell forever, I decided to start working on something similar.

Progress was slow over the past week, but today I had joined the meeting with a fresh pair of eyes and a determination to finally drag myself out of this mess. While normally I would use terminal applications to navigate a local copy of the project I was using, during the last meeting I was given a link to something directly in the repository - the aforementioned Helm chart, stuffed into an internal directory, never to be seen again. Going back to my local repository, I noticed that there were newer tags available than what I was using, so I quickly updated to a new version of the repository, and noticed something sent from the angels to pull me up from hell: the latest tag had moved the Helm chart from the internal location to an easily accessible charts directory.

Using the tool khelm, I was able to render a Helm chart of the Calico project with some reasonably sane defaults: use BPF, deploy some additional components in case I'll use them later, and use Calico without any additional layer such as Flannel. With the resulting YAML file, I was able to yoink out individual parts and put them into their own reasonably named collection of resources in the Kustomization I had created for the project. After that, I was able to build the Calico manifests locally and deploy to the Kubernetes cluster. The results were less than ideal: as a DaemonSet had been left in CrashLoopBackoff and all the other pods were stuck Pending, I noticed two essential missing value in the Calico ConfigMap: a hostname and port pair. Because the BPF interoperability affected the way kube-proxy worked, the CNI pods were not able to route to the Kubernetes server, and had to be configured with a manual address.

This leads to probably my least favorite component of the system I've designed. While most of the resources can be deployed without hardcoding any kind of option, and most options can be reused between clusters, there's no good way that I saw to create a ConfigMap component that could hold the connection information for my cluster. I instead had to hack a kubeconfig file out of my Talos configuration - removing the ability to easily merge it later - and use a null resource to provision the ConfigMap. However, once it was all completed, the cluster was once again rebuilt. Loading up k9s -c nodes, I was able to see a list of Nodes reporting that they were Ready, which meant that the CNI was up and correctly working.

And so I ascend from hell. For now.

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