---
reviewers:
- vishh
- derekwaynecarr
- dashpole
title: Reserve Compute Resources for System Daemons
content_type: task
weight: 290
---
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Kubernetes nodes can be scheduled to `Capacity`. Pods can consume all the
available capacity on a node by default. This is an issue because nodes
typically run quite a few system daemons that power the OS and Kubernetes
itself. Unless resources are set aside for these system daemons, pods and system
daemons compete for resources and lead to resource starvation issues on the
node.
The `kubelet` exposes a feature named 'Node Allocatable' that helps to reserve
compute resources for system daemons. Kubernetes recommends cluster
administrators to configure 'Node Allocatable' based on their workload density
on each node.
## {{% heading "prerequisites" %}}
{{< include "task-tutorial-prereqs.md" >}}
You can configure below kubelet [configuration settings](/docs/reference/config-api/kubelet-config.v1beta1/)
using the [kubelet configuration file](/docs/tasks/administer-cluster/kubelet-config-file/).
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## Node Allocatable
'Allocatable' on a Kubernetes node is defined as the amount of compute resources
that are available for pods. The scheduler does not over-subscribe
'Allocatable'. 'CPU', 'memory' and 'ephemeral-storage' are supported as of now.
Node Allocatable is exposed as part of `v1.Node` object in the API and as part
of `kubectl describe node` in the CLI.
Resources can be reserved for two categories of system daemons in the `kubelet`.
### Enabling QoS and Pod level cgroups
To properly enforce node allocatable constraints on the node, you must
enable the new cgroup hierarchy via the `cgroupsPerQOS` setting. This setting is
enabled by default. When enabled, the `kubelet` will parent all end-user pods
under a cgroup hierarchy managed by the `kubelet`.
### Configuring a cgroup driver
The `kubelet` supports manipulation of the cgroup hierarchy on
the host using a cgroup driver. The driver is configured via the `cgroupDriver` setting.
The supported values are the following:
* `cgroupfs` is the default driver that performs direct manipulation of the
cgroup filesystem on the host in order to manage cgroup sandboxes.
* `systemd` is an alternative driver that manages cgroup sandboxes using
transient slices for resources that are supported by that init system.
Depending on the configuration of the associated container runtime,
operators may have to choose a particular cgroup driver to ensure
proper system behavior. For example, if operators use the `systemd`
cgroup driver provided by the `containerd` runtime, the `kubelet` must
be configured to use the `systemd` cgroup driver.
### Kube Reserved
- **KubeletConfiguration Setting**: `kubeReserved: {}`. Example value `{cpu: 100m, memory: 100Mi, ephemeral-storage: 1Gi, pid=1000}`
- **KubeletConfiguration Setting**: `kubeReservedCgroup: ""`
`kubeReserved` is meant to capture resource reservation for kubernetes system
daemons like the `kubelet`, `container runtime`, etc.
It is not meant to reserve resources for system daemons that are run as pods.
`kubeReserved` is typically a function of `pod density` on the nodes.
In addition to `cpu`, `memory`, and `ephemeral-storage`, `pid` may be
specified to reserve the specified number of process IDs for
kubernetes system daemons.
To optionally enforce `kubeReserved` on kubernetes system daemons, specify the parent
control group for kube daemons as the value for `kubeReservedCgroup` setting,
and [add `kube-reserved` to `enforceNodeAllocatable`](#enforcing-node-allocatable).
It is recommended that the kubernetes system daemons are placed under a top
level control group (`runtime.slice` on systemd machines for example). Each
system daemon should ideally run within its own child control group. Refer to
[the design proposal](https://git.k8s.io/design-proposals-archive/node/node-allocatable.md#recommended-cgroups-setup)