I've been sketching out the architecture of a basic Kubernetes system with local path providers and Flannel to grasp how everything fits together. It seems like there are a ton of "containers" running even for basic functionalities, like how kube-proxy manages the host's ip-table. I'm curious: these containers don't seem to be the typical Docker containers with a full OS, since even a lightweight OS would add too much overhead for such simple tasks. Can anyone break down what exactly the containers in a pod are? Are they similar to AWS Lambda or Azure Functions, which consist of small pieces of code executing quickly? I thought those also come with a ready-to-deploy container and an OS, so what's the difference?
7 Answers
While I'm no expert, diving into how namespace isolation works in containers can help. Containers can isolate various aspects like network and filesystems, which allows them to share some resources while maintaining a level of independence. For example, a Go binary might only need one file to run since it's statically linked, while something like Nginx requires more components. Think of Lambda and Azure Functions as similar to one-off containers—they start, do their job, and exit.
The containers inside a pod are really just that—containers that run packaged applications. For instance, in the case of kube-proxy, the application is specifically designed to make network changes on the host.
Kubernetes components often use distroless images or even just an empty image, which means they don't include a full OS. Instead, they might only have a statically linked binary, which is super lightweight—no unnecessary overhead here!
To put it simply, containers are about process isolation. They create a kind of barrier allowing each process to have its own space without interference. This means they can look like independent systems. Most real-world programs do need some dependencies, but if you build your app carefully, you can have just the app in the container without bloated OS files. Distroless images can help you keep things minimal depending on your programming language.
For visualizing and generating Kubernetes configurations, you might want to check out this tool: https://kube-composer.com. It’s a handy resource!
Interestingly, while Docker was traditionally used for running containers, Kubernetes has shifted to using containerd now to help avoid the lock-in issues that came with Docker.
I think it's key to understand how container images are built. Unlike VMs, containers share the host's kernel, meaning they don't operate like traditional OS environments. The size of container images matters, and those used in Kubernetes are optimized for performance, minimizing overhead.
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