Running Kubernetes Node Components as a Non-root User
Kubernetes v1.22 [alpha]
This document describes how to run Kubernetes Node components such as kubelet, CRI, OCI, and CNI without root privileges, by using a user namespace.
This technique is also known as rootless mode.
This document describes how to run Kubernetes Node components (and hence pods) as a non-root user.
If you are just looking for how to run a pod as a non-root user, see SecurityContext.
Before you begin
Your Kubernetes server must be at or later than version 1.22.
To check the version, enter
- Enable Cgroup v2
- Enable systemd with user session
- Configure several sysctl values, depending on host Linux distribution
- Ensure that your unprivileged user is listed in
- Enable the
Running Kubernetes inside Rootless Docker/Podman
kind supports running Kubernetes inside Rootless Docker or Rootless Podman.
minikube also supports running Kubernetes inside Rootless Docker or Rootless Podman.
See the Minikube documentation:
Running Kubernetes inside Unprivileged Containers
Sysbox is an open-source container runtime (similar to "runc") that supports running system-level workloads such as Docker and Kubernetes inside unprivileged containers isolated with the Linux user namespace.
See Sysbox Quick Start Guide: Kubernetes-in-Docker for more info.
Sysbox supports running Kubernetes inside unprivileged containers without
requiring Cgroup v2 and without the
KubeletInUserNamespace feature gate. It
does this by exposing specially crafted
/sys filesystems inside
the container plus several other advanced OS virtualization techniques.
Running Rootless Kubernetes directly on a host
K3s experimentally supports rootless mode.
See Running K3s with Rootless mode for the usage.
Usernetes is a reference distribution of Kubernetes that can be installed under
$HOME directory without the root privilege.
Usernetes supports both containerd and CRI-O as CRI runtimes. Usernetes supports multi-node clusters using Flannel (VXLAN).
See the Usernetes repo for the usage.
Manually deploy a node that runs the kubelet in a user namespace
This section provides hints for running Kubernetes in a user namespace manually.
Creating a user namespace
The first step is to create a user namespace.
If you are trying to run Kubernetes in a user-namespaced container such as Rootless Docker/Podman or LXC/LXD, you are all set, and you can go to the next subsection.
Otherwise you have to create a user namespace by yourself, by calling
A user namespace can be also unshared by using command line tools such as:
After unsharing the user namespace, you will also have to unshare other namespaces such as mount namespace.
You do not need to call
pivot_root() after unsharing the mount namespace,
however, you have to mount writable filesystems on several directories in the namespace.
At least, the following directories need to be writable in the namespace (not outside the namespace):
Creating a delegated cgroup tree
In addition to the user namespace, you also need to have a writable cgroup tree with cgroup v2.
If you are trying to run Kubernetes in Rootless Docker/Podman or LXC/LXD on a systemd-based host, you are all set.
Otherwise you have to create a systemd unit with
Delegate=yes property to delegate a cgroup tree with writable permission.
On your node, systemd must already be configured to allow delegation; for more details, see cgroup v2 in the Rootless Containers documentation.
The network namespaces of the Pods can be configured with regular CNI plugins. For multi-node networking, Flannel (VXLAN, 8472/UDP) is known to work.
Ports such as the kubelet port (10250/TCP) and
NodePort service ports have to be exposed from the Node network namespace to
the host with an external port forwarder, such as RootlessKit, slirp4netns, or
The kubelet relies on a container runtime. You should deploy a container runtime such as containerd or CRI-O and ensure that it is running within the user namespace before the kubelet starts.
Running CRI plugin of containerd in a user namespace is supported since containerd 1.4.
Running containerd within a user namespace requires the following configurations.
version = 2 [plugins."io.containerd.grpc.v1.cri"] # Disable AppArmor disable_apparmor = true # Ignore an error during setting oom_score_adj restrict_oom_score_adj = true # Disable hugetlb cgroup v2 controller (because systemd does not support delegating hugetlb controller) disable_hugetlb_controller = true [plugins."io.containerd.grpc.v1.cri".containerd] # Using non-fuse overlayfs is also possible for kernel >= 5.11, but requires SELinux to be disabled snapshotter = "fuse-overlayfs" [plugins."io.containerd.grpc.v1.cri".containerd.runtimes.runc.options] # We use cgroupfs that is delegated by systemd, so we do not use SystemdCgroup driver # (unless you run another systemd in the namespace) SystemdCgroup = false
The default path of the configuration file is
The path can be specified with
containerd -c /path/to/containerd/config.toml.
Running CRI-O in a user namespace is supported since CRI-O 1.22.
CRI-O requires an environment variable
_CRIO_ROOTLESS=1 to be set.
The following configurations are also recommended:
[crio] storage_driver = "overlay" # Using non-fuse overlayfs is also possible for kernel >= 5.11, but requires SELinux to be disabled storage_option = ["overlay.mount_program=/usr/local/bin/fuse-overlayfs"] [crio.runtime] # We use cgroupfs that is delegated by systemd, so we do not use "systemd" driver # (unless you run another systemd in the namespace) cgroup_manager = "cgroupfs"
The default path of the configuration file is
The path can be specified with
crio --config /path/to/crio/crio.conf.
Running kubelet in a user namespace requires the following configuration:
apiVersion: kubelet.config.k8s.io/v1beta1 kind: KubeletConfiguration featureGates: KubeletInUserNamespace: true # We use cgroupfs that is delegated by systemd, so we do not use "systemd" driver # (unless you run another systemd in the namespace) cgroupDriver: "cgroupfs"
KubeletInUserNamespace feature gate is enabled, the kubelet ignores errors
that may happen during setting the following sysctl values on the node.
Within a user namespace, the kubelet also ignores any error raised from trying to open
This feature gate also allows kube-proxy to ignore an error during setting
KubeletInUserNamespace feature gate was introduced in Kubernetes v1.22 with "alpha" status.
Running kubelet in a user namespace without using this feature gate is also possible by mounting a specially crafted proc filesystem (as done by Sysbox), but not officially supported.
Running kube-proxy in a user namespace requires the following configuration:
apiVersion: kubeproxy.config.k8s.io/v1alpha1 kind: KubeProxyConfiguration mode: "iptables" # or "userspace" conntrack: # Skip setting sysctl value "net.netfilter.nf_conntrack_max" maxPerCore: 0 # Skip setting "net.netfilter.nf_conntrack_tcp_timeout_established" tcpEstablishedTimeout: 0s # Skip setting "net.netfilter.nf_conntrack_tcp_timeout_close" tcpCloseWaitTimeout: 0s
Most of "non-local" volume drivers such as
iscsido not work. Local volumes like
downwardAPIare known to work.
Some CNI plugins may not work. Flannel (VXLAN) is known to work.
For more on this, see the Caveats and Future work page on the rootlesscontaine.rs website.
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