Usernetes: Kubernetes without the root privileges (Generation 2)

Usernetes (Gen2) deploys a Kubernetes cluster inside Rootless Docker, so as to mitigate potential container-breakout vulnerabilities.

Note

Usernetes (Gen2) has significantly diverged from the original Usernetes (Gen1), which did not require Rootless Docker to be installed on hosts.

See the gen1 branch for the original Usernetes (Gen1).

Usernetes (Gen2) is similar to Rootless kind and Rootless minikube, but Usernetes (Gen 2) supports creating a cluster with multiple hosts.

Components

• Cluster configuration: kubeadm
• CRI: containerd
• OCI: runc
• CNI: Flannel

Requirements

• One of the following host operating system:

Host operating system	Minimum version
Ubuntu (recommended)	22.04
Rocky Linux	9
AlmaLinux	9
Fedora	(?)

• One of the following container engines:

Container Engine	Minimum version
Rootless Docker (recommended)	v20.10
Rootless Podman	v4.x
Rootless nerdctl	v1.6

curl -o install.sh -fsSL https://get.docker.com
sudo sh install.sh
dockerd-rootless-setuptool.sh install

• systemd lingering:

sudo loginctl enable-linger $(whoami)

• cgroup v2 delegation:

sudo mkdir -p /etc/systemd/system/[email protected]

sudo tee /etc/systemd/system/[email protected]/delegate.conf <<EOF >/dev/null
[Service]
Delegate=cpu cpuset io memory pids
EOF

sudo systemctl daemon-reload

• Kernel modules:

sudo tee /etc/modules-load.d/usernetes.conf <<EOF >/dev/null
br_netfilter
vxlan
EOF

sudo systemctl restart systemd-modules-load.service

• sysctl:

sudo tee /etc/sysctl.d/99-usernetes.conf <<EOF >/dev/null
net.ipv4.conf.default.rp_filter = 2
EOF

sudo sysctl --system

• slirp4netns, not Pasta:

# Podman v5 (or later) users have to change the network mode from pasta to slirp4netns.
# This step is not needed for Docker, nerdctl, and Podman v4.

mkdir -p "$HOME/.config/containers/containers.conf.d"
cat <<EOF >"$HOME/.config/containers/containers.conf.d/slirp4netns.conf"
[network]
default_rootless_network_cmd="slirp4netns"
EOF

Use scripts in ./init-host for automating these steps.

Usage

See make help.

# Bootstrap a cluster
make up
make kubeadm-init
make install-flannel

# Enable kubectl
make kubeconfig
export KUBECONFIG=$(pwd)/kubeconfig
kubectl get pods -A

# Multi-host
make join-command
scp join-command another-host:~/usernetes
ssh another-host make -C ~/usernetes up kubeadm-join
make sync-external-ip

# Debug
make logs
make shell
make kubeadm-reset
make down-v
kubectl taint nodes --all node-role.kubernetes.io/control-plane-

The container engine defaults to Docker. To change the container engine, set export CONTAINER_ENGINE=podman or export CONTAINER_ENGINE=nerdctl.

Limitations

• Node ports cannot be exposed automatically. Edit docker-compose.yaml for exposing additional node ports.
• Most of host files are not visible with hostPath mounts. Edit docker-compose.yaml for mounting additional files.
• Some volume drivers such as nfs do not work.

Advanced topics

Network

When CONTAINER_ENGINE is set to nerdctl, bypass4netns can be enabled for accelerating connect(2) syscalls. The acceleration currently does not apply to VXLAN packets.

containerd-rootless-setuptool.sh install-bypass4netnsd
export CONTAINER_ENGINE=nerdctl
make up

Note

The support for bypass4netns is still experimental

Misc

• Although Usernetes (Gen2) is designed to be used with Rootless Docker, it should work with the regular "rootful" Docker too. This might be useful for some people who are looking for "multi-host" version of kind and minikube.