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Usernetes: Kubernetes without the root privileges

Usernetes aims to provide a reference distribution of Kubernetes that can be installed under a user's $HOME and does not require the root privileges.

Included components

  • Installer scripts
  • Rootless Containers infrastructure (RootlessKit, slirp4netns, and fuse-overlayfs)
  • Master components (etcd, kube-apiserver, ...)
  • Node components (kubelet and kube-proxy)
  • CRI runtimes
    • containerd (default)
    • CRI-O
  • OCI runtime
    • crun
  • Multi-node CNI
    • Flannel (VXLAN)
    • Calico (VXLAN)
  • CoreDNS

Installer scripts are in POC status.

See Adoption for Usernetes-based Kubernetes distributions.

Note

Usernetes no longer includes Docker (Moby) binaries since February 2020.

To install Rootless Docker, see https://get.docker.com/rootless .

See also https://docs.docker.com/engine/security/rootless/ for the further information.

Adoption

We encourage other Kubernetes distributions to adopt Usernetes.

Currently, the following distributions adopt Usernetes:

How it works

Usernetes executes Kubernetes and CRI runtimes without the root privileges by using unprivileged user_namespaces(7), mount_namespaces(7), and network_namespaces(7).

To set up NAT across the host and the network namespace without the root privilege, Usernetes uses a usermode network stack (slirp4netns).

No SETUID/SETCAP binary is needed, except newuidmap(1) and newgidmap(1), which are used for setting up user_namespaces(7) with multiple sub-UIDs and sub-GIDs.

Restrictions

  • Usermode networking called slirp4netns is used instead of kernel-mode vEth pairs.
  • fuse-overlayfs is used instead of kernel-mode overlayfs.
  • Node ports are network-namespaced
  • Apparmor is unsupported

Requirements

Recommended host distributions are Ubuntu 22.04 and Fedora 38.

The following requirements have to be satisfied:

  • Kernel >= 4.18.

  • cgroup v2.

  • Recent version of systemd. Known to work with systemd >= 242.

  • mount.fuse3 binary. Provided by fuse3 package on most distros.

  • iptables binary. Provided by iptables package on most distros.

  • conntrack binary. Provided by conntrack package on most distros.

  • newuidmap and newgidmap binaries. Provided by uidmap package on most distros.

  • /etc/subuid and /etc/subgid should contain more than 65536 sub-IDs. e.g. exampleuser:231072:65536. These files are automatically configured on most distros.

$ id -u
1001
$ whoami
exampleuser
$ grep "^$(whoami):" /etc/subuid
exampleuser:231072:65536
$ grep "^$(whoami):" /etc/subgid
exampleuser:231072:65536
  • The following kernel modules to be loaded:
fuse
tun
tap
bridge
br_netfilter
veth
ip_tables
ip6_tables
iptable_nat
ip6table_nat
iptable_filter
ip6table_filter
nf_tables
x_tables
xt_MASQUERADE
xt_addrtype
xt_comment
xt_conntrack
xt_mark
xt_multiport
xt_nat
xt_tcpudp

On older kernels, xt_MASQUERADE should be ipt_MASQUERADE and ip6t_MASQUERADE.

cgroup v2

The host needs to be running with cgroup v2.

If /sys/fs/cgroup/cgroup.controllers is present on your system, you are using v2, otherwise you are using v1.

To enable cgroup v2, add systemd.unified_cgroup_hierarchy=1 to the GRUB_CMDLINE_LINUX line in /etc/default/grub and run sudo update-grub.

If grubby command is available on your system, this step can be also accomplished with sudo grubby --update-kernel=ALL --args="systemd.unified_cgroup_hierarchy=1".

Enable cpu controller

Typically, only memory and pids controllers are delegated to non-root users by default.

$ cat /sys/fs/cgroup/user.slice/user-$(id -u).slice/user@$(id -u).service/cgroup.subtree_control
memory pids

To allow delegation of all controllers, you need to change the systemd configuration as follows:

# mkdir -p /etc/systemd/system/[email protected]
# cat > /etc/systemd/system/[email protected]/delegate.conf << EOF
[Service]
Delegate=yes
EOF
# systemctl daemon-reload

You have to re-login or reboot the host after changing the systemd configuration. Rebooting is recommended.

Quick start

Download

Download the latest usernetes-x86_64.tbz from Releases.

$ tar xjvf usernetes-x86_64.tbz
$ cd usernetes

Install

install.sh installs Usernetes systemd units to $HOME/.config/systemd/unit.

To use containerd as the CRI runtime (default):

$ ./install.sh --cri=containerd
[INFO] Base dir: /home/exampleuser/gopath/src/github.com/rootless-containers/usernetes
[INFO] Installing /home/exampleuser/.config/systemd/user/u7s.target
[INFO] Installing /home/exampleuser/.config/systemd/user/u7s-rootlesskit.service
[INFO] Installing /home/exampleuser/.config/systemd/user/u7s-etcd.target
[INFO] Installing /home/exampleuser/.config/systemd/user/u7s-etcd.service
[INFO] Installing /home/exampleuser/.config/systemd/user/u7s-master.target
[INFO] Installing /home/exampleuser/.config/systemd/user/u7s-kube-apiserver.service
[INFO] Installing /home/exampleuser/.config/systemd/user/u7s-kube-controller-manager.service
[INFO] Installing /home/exampleuser/.config/systemd/user/u7s-kube-scheduler.service
[INFO] Installing /home/exampleuser/.config/systemd/user/u7s-node.target
[INFO] Installing /home/exampleuser/.config/systemd/user/u7s-containerd.service
[INFO] Installing /home/exampleuser/.config/systemd/user/u7s-kubelet-containerd.service
[INFO] Installing /home/exampleuser/.config/systemd/user/u7s-kube-proxy.service
[INFO] Starting u7s.target
+ systemctl --user -T enable u7s.target
Created symlink /home/exampleuser/.config/systemd/user/multi-user.target.wants/u7s.target → /home/exampleuser/.config/systemd/user/u7s.target.
+ systemctl --user -T start u7s.target
Enqueued anchor job 522 u7s.target/start.
Enqueued auxiliary job 538 u7s-rootlesskit.service/start.
Enqueued auxiliary job 542 u7s-kubelet-containerd.service/start.
Enqueued auxiliary job 541 u7s-containerd.service/start.
Enqueued auxiliary job 524 u7s-etcd.service/start.
Enqueued auxiliary job 546 u7s-kube-controller-manager.service/start.
Enqueued auxiliary job 523 u7s-etcd.target/start.
Enqueued auxiliary job 543 u7s-master.target/start.
Enqueued auxiliary job 544 u7s-kube-scheduler.service/start.
Enqueued auxiliary job 545 u7s-kube-apiserver.service/start.
Enqueued auxiliary job 539 u7s-node.target/start.
Enqueued auxiliary job 540 u7s-kube-proxy.service/start.
+ systemctl --user --no-pager status
● localhost
    State: running
...
[INFO] Installation complete.
[INFO] Hint: `sudo loginctl enable-linger` to start user services automatically on the system start up.
[INFO] Hint: export KUBECONFIG=/home/exampleuser/.config/usernetes/master/admin-localhost.kubeconfig

CoreDNS is automatically enabled since November 2021. Older releases of Usernetes had required installing CoreDNS from manifests/coredns.yaml.

To use CRI-O:

$ ./install.sh --cri=crio

Use kubectl

$ export KUBECONFIG="$HOME/.config/usernetes/master/admin-localhost.kubeconfig"
$ kubectl get nodes -o wide

Uninstall

$ ./uninstall.sh

To remove data files:

$ ./show-cleanup-command.sh
$ eval $(./show-cleanup-command.sh)

Run Usernetes in Docker

All-in-one Docker image is available as ghcr.io/rootless-containers/usernetes on GHCR.

⚠️ rootlesscontainers/usernetes on Docker Hub is no longer updated. Please use the GHCR image.

To build the image manually:

$ docker build -t ghcr.io/rootless-containers/usernetes .

The image is based on Fedora.

Single node

$ docker run -td --name usernetes-node -p 127.0.0.1:6443:6443 --privileged ghcr.io/rootless-containers/usernetes --cri=containerd

Wait until docker ps shows "healty" as the status of usernetes-node container.

$ docker cp usernetes-node:/home/user/.config/usernetes/master/admin-localhost.kubeconfig docker.kubeconfig
$ export KUBECONFIG=./docker.kubeconfig
$ kubectl run -it --rm --image busybox foo
/ #

Multi node (Docker Compose)

$ make up
$ export KUBECONFIG=$HOME/.config/usernetes/docker-compose.kubeconfig

Flannel VXLAN 10.5.0.0/16 is configured by default.

$ kubectl get nodes -o wide
NAME           STATUS   ROLES    AGE     VERSION           INTERNAL-IP    EXTERNAL-IP   OS-IMAGE             KERNEL-VERSION      CONTAINER-RUNTIME
967e81e90e1f   Ready    <none>   3m42s   v1.14-usernetes   10.0.101.100   <none>        Ubuntu 18.04.1 LTS   4.15.0-43-generic   docker://Unknown
b2204f192e5c   Ready    <none>   3m42s   v1.14-usernetes   10.0.102.100   <none>        Ubuntu 18.04.1 LTS   4.15.0-43-generic   cri-o://1.14.0-dev
ba0133c68378   Ready    <none>   3m42s   v1.14-usernetes   10.0.103.100   <none>        Ubuntu 18.04.1 LTS   4.15.0-43-generic   containerd://1.2.0-168-gb3807c5d
$ kubectl run --replicas=3 --image=nginx:alpine nginx
$ kubectl get pods -o wide
NAME                     READY   STATUS    RESTARTS   AGE   IP          NODE           NOMINATED NODE   READINESS GATES
nginx-6b4b85b77b-7hqrk   1/1     Running   0          3s    10.5.13.3   b2204f192e5c   <none>           <none>
nginx-6b4b85b77b-8rknj   1/1     Running   0          3s    10.5.79.3   967e81e90e1f   <none>           <none>
nginx-6b4b85b77b-r466s   1/1     Running   0          3s    10.5.7.3    ba0133c68378   <none>           <none>
$ kubectl exec -it nginx-6b4b85b77b-7hqrk -- wget -O - http://10.5.79.3
Connecting to 10.5.79.3 (10.5.79.3:80)
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
...
$ kubectl exec -it nginx-6b4b85b77b-7hqrk -- wget -O - http://10.5.7.3
Connecting to 10.5.7.3 (10.5.7.3:80)
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
...

Advanced guide

Expose netns ports to the host

As Usernetes runs in a network namespace (with slirp4netns), you can't expose container ports to the host by just running kubectl expose --type=NodePort.

In addition, you need to expose Usernetes netns ports to the host:

$ ./rootlessctl.sh add-ports 0.0.0.0:30080:30080/tcp

You can also manually expose Usernetes netns ports manually with socat:

$ pid=$(cat $XDG_RUNTIME_DIR/usernetes/rootlesskit/child_pid)
$ socat -t -- TCP-LISTEN:30080,reuseaddr,fork EXEC:"nsenter -U -n -t $pid socat -t -- STDIN TCP4\:127.0.0.1\:30080"

Routing ping packets

To route ping packets, you may need to set up net.ipv4.ping_group_range properly as the root.

$ sudo sh -c "echo 0   2147483647  > /proc/sys/net/ipv4/ping_group_range"

IP addresses

  • 10.0.0.0/24: The CIDR for the Kubernetes ClusterIP services

    • 10.0.0.1: The kube-apiserver ClusterIP
    • 10.0.0.53: The CoreDNS ClusterIP

  • 10.0.42.0/24: The default CIDR for the RootlessKit network namespace. Can be overridden with install.sh --cidr=<CIDR>.

    • 10.0.42.2: The slirp4netns gateway
    • 10.0.42.3: The slirp4netns DNS
    • 10.0.42.100: The slirp4netns TAP device

  • 10.0.100.0/24: The CIDR used instead of 10.0.42.0/24 in Docker Compose master

  • 10.0.101.0/24: The CIDR used instead of 10.0.42.0/24 in Docker Compose containerd node

  • 10.0.102.0/24: The CIDR used instead of 10.0.42.0/24 in Docker Compose CRI-O node

  • 10.5.0.0/16: The CIDR for Flannel

  • 10.88.0.0/16: The CIDR for single-node CNI and Calico

Install Usernetes from source

Docker 17.05+ is required for building Usernetes from the source. Docker 18.09+ with DOCKER_BUILDKIT=1 is recommended.

$ make

Binaries are generated under ./bin directory.

License

Usernetes is licensed under the terms of Apache License Version 2.0.

The binary releases of Usernetes contain files that are licensed under the terms of different licenses:

About

Kubernetes installable under $HOME, without the root privileges

github.com/kubernetes/enhancements/tree/master/keps/sig-node/2033-kubelet-in-userns-aka-rootless

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