Kubernetes development cluster bootstrapping with Nix packages

This project aims to provide single dependency Kubernetes clusters for local testing, experimenting and development purposes.

Moving pictures are worth more than thousand words, so here is a short demo:

Nix?

Have you ever heard about Nix, the functional package manager?

In case you haven't, don’t worry – the important thing is that it provides all the third-party dependencies needed for this project, pinned to a dedicated version. This guarantees stable, reproducible installations.

KuberNix itself is a Rusty helper program, which takes care of bootstrapping the Kubernetes cluster, passing the right configuration parameters around and keeping track of the running processes.

What is inside

The following technology stack is currently being used:

Application	Version
cfssl	v1.5.0
cni-plugins	v0.9.0
conmon	v2.0.25
conntrack-tools	v1.4.6
cri-o-wrapper	v1.20.0
cri-tools	v1.20.0
etcd	v3.3.25
iproute2	v5.10.0
iptables	v1.8.6
kmod	v27
kubectl	v1.19.5
kubernetes	v1.19.5
nss-cacert	v3.60
podman-wrapper	v2.2.1
runc	v1.0.0-rc92
socat	v1.7.4.1
sysctl	v1003.1.2008
util-linux	v2.36.1

Some other tools are not explicitly mentioned here, because they are no first-level dependencies.

Single Dependency

With Nix

As already mentioned, there is only one single dependency needed to run this project: Nix. To setup Nix, simply run:

$ curl https://nixos.org/nix/install | sh

Please make sure to follow the instructions output by the script.

With the Container Runtime of your Choice

It is also possible to run KuberNix in the container runtime of your choice. To do this, simply grab the latest image from saschagrunert/kubernix. Please note that running KuberNix inside a container image requires to run privileged mode and host networking. For example, we can run KuberNix with podman like this:

$ sudo podman run \
    --net=host \
    --privileged \
    -it docker.io/saschagrunert/kubernix:latest

Getting Started

Cluster Bootstrap

To bootstrap your first cluster, download one of the latest release binaries or build the application via:

$ make build-release

The binary should now be available in the target/release/kubernix directory of the project. Alternatively, install the application via cargo install kubernix.

After the successful binary retrieval, start KuberNix by running it as root:

$ sudo kubernix

KuberNix will now take care that the Nix environment gets correctly setup, downloads the needed binaries and starts the cluster. Per default it will create a directory called kubernix-run in the current path which contains all necessary data for the cluster.

Shell Environment

If everything went fine, you should be dropped into a new shell session, like this:

[INFO ] Everything is up and running
[INFO ] Spawning interactive shell
[INFO ] Please be aware that the cluster stops if you exit the shell
>

Now you can access your cluster via tools like kubectl:

> kubectl get pods --all-namespaces
NAMESPACE     NAME                       READY   STATUS    RESTARTS   AGE
kube-system   coredns-85d84dd694-xz997   1/1     Running   0          102s

All configuration files have been written to the target directory, which is now the current one:

> ls -1
apiserver/
controllermanager/
coredns/
crio/
encryptionconfig/
etcd/
kubeconfig/
kubelet/
kubernix.env
kubernix.toml
nix/
pki/
policy.json
proxy/
scheduler/

For example, the log files for the different running components are now available within their corresponding directory:

> ls -1 **.log
apiserver/kube-apiserver.log
controllermanager/kube-controller-manager.log
crio/crio.log
etcd/etcd.log
kubelet/kubelet.log
proxy/kube-proxy.log
scheduler/kube-scheduler.log

If you want to spawn an additional shell session, simply run kubernix shell in the same directory as where the initial bootstrap happened.

$ sudo kubernix shell
[INFO  kubernix] Spawning new kubernix shell in 'kubernix-run'
> kubectl run --generator=run-pod/v1 --image=alpine -it alpine sh
If you don't see a command prompt, try pressing enter.
/ #

This means that you can spawn as many shells as you want to.

Cleanup

The whole cluster gets automatically destroyed if you exit the shell session from the initial process:

> exit
[INFO ] Cleaning up

Please note that the directory where all the data is stored is not being removed after the exit of KuberNix. This means that you’re still able to access the log and configuration files for further processing. If you start the cluster again, then the cluster files will be reused. This is especially handy if you want to test configuration changes.

Restart

If you start KuberNix again in the same run directory, then it will re-use the configuration during the cluster bootstrapping process. This means that you can modify all data inside the run root for testing and debugging purposes. The startup of the individual components will be initiated by YAML files called run.yml, which are available inside the directories of the corresponding components. For example, etc gets started via:

> cat kubernix-run/etcd/run.yml

---
command: /nix/store/qlbsv0hvi0j5qj3631dzl9srl75finlk-etcd-3.3.13-bin/bin/etcd
args:
  - "--advertise-client-urls=https://127.0.0.1:2379"
  - "--client-cert-auth"
  - "--data-dir=/…/kubernix-run/etcd/run"
  - "--initial-advertise-peer-urls=https://127.0.0.1:2380"
  - "--initial-cluster-state=new"
  - "--initial-cluster-token=etcd-cluster"
  - "--initial-cluster=etcd=https://127.0.0.1:2380"
  - "--listen-client-urls=https://127.0.0.1:2379"
  - "--listen-peer-urls=https://127.0.0.1:2380"
  - "--name=etcd"
  - "--peer-client-cert-auth"
  - "--cert-file=/…/kubernix-run/pki/kubernetes.pem"
  - "--key-file=/…/kubernix-run/pki/kubernetes-key.pem"
  - "--peer-cert-file=/…/kubernix-run/pki/kubernetes.pem"
  - "--peer-key-file=/…/kubernix-run/pki/kubernetes-key.pem"
  - "--peer-trusted-ca-file=/…/kubernix-run/pki/ca.pem"
  - "--trusted-ca-file=/…/kubernix-run/pki/ca.pem"

Configuration

KuberNix has some configuration possibilities, which are currently:

CLI argument	Description	Default	Environment Variable
-r, --root	Path where all the runtime data is stored	kubernix-run	KUBERNIX_ROOT
-l, --log-level	Logging verbosity	info	KUBERNIX_LOG_LEVEL
-c, --cidr	CIDR used for the cluster network	10.10.0.0/16	KUBERNIX_CIDR
-s, --shell	The shell executable to be used	$SHELL/sh	KUBERNIX_SHELL
-e, --no-shell	Do not spawn an interactive shell after bootstrap	false	KUBERNIX_NO_SHELL
-n, --nodes	The number of nodes to be registered	1	KUBERNIX_NODES
-u, --container-runtime	The container runtime to be used for the nodes, irrelevant if nodes equals to 1	podman	KUBERNIX_CONTAINER_RUNTIME
-o, --overlay	Nix package overlay to be used		KUBERNIX_OVERLAY
-p, --packages	Additional Nix dependencies to be added to the environment		KUBERNIX_PACKAGES

Please ensure that the CIDR is not overlapping with existing local networks and that your setup has access to the internet. The CIDR will be automatically split up over the necessary cluster components.

Multinode Support

It is possible to spawn multiple worker nodes, too. To do this, simply adjust the -n, --nodes command line argument as well as your preferred container runtime via -u, --container-runtime. The default runtime is podman, but every other Docker drop-in replacement should work out of the box.

Overlays

Overlays provide a method to extend and change Nix derivations. This means, that we’re able to change dependencies during the cluster bootstrapping process. For example, we can exchange the used CRI-O version to use a local checkout by writing this simple overlay.nix:

self: super: {
  cri-o = super.cri-o.overrideAttrs(old: {
    src = ../path/to/go/src/github.com/cri-o/cri-o;
  });
}

Now we can run KuberNix with the --overlay, -o command line argument:

$ sudo kubernix --overlay overlay.nix
[INFO  kubernix] Nix environment not found, bootstrapping one
[INFO  kubernix] Using custom overlay 'overlay.nix'
these derivations will be built:
  /nix/store/9jb43i2mqjc94mbx30d9nrx529w6lngw-cri-o-1.15.2.drv
  building '/nix/store/9jb43i2mqjc94mbx30d9nrx529w6lngw-cri-o-1.15.2.drv'...

Using this technique makes it easy for daily development of Kubernetes components, by simply changing it to local paths or trying out new versions.

Additional Packages

It is also possible to add additional packages to the KuberNix environment by specifying them via the --packages, -p command line parameter. This way you can easily utilize additional tools in a reproducible way. For example, when to comes to using always the same Helm version, you could simply run:

$ sudo kubernix -p kubernetes-helm
[INFO ] Nix environment not found, bootstrapping one
[INFO ] Bootstrapping cluster inside nix environment
…
> helm init
> helm version
Client: &version.Version{SemVer:"v2.14.3", GitCommit:"", GitTreeState:"clean"}
Server: &version.Version{SemVer:"v2.14.3", GitCommit:"0e7f3b6637f7af8fcfddb3d2941fcc7cbebb0085", GitTreeState:"clean"}

All available packages are listed on the official Nix index.

Contributing

You want to contribute to this project? Wow, thanks! So please just fork it and send me a pull request.