Configuring swap memory on Kubernetes nodes [page]deterministic

tutorials

This page provides an example of how to provision and configure swap memory on a Kubernetes node using kubeadm.

* Provision swap memory on a Kubernetes node using kubeadm. * Learn to configure both encrypted and unencrypted swap. * Learn to enable swap on boot.

You need at least one worker node in your cluster which needs to run a Linux operating system. It is required for this demo that the kubeadm tool be installed, following the steps outlined in the [kubeadm installation guide](/docs/setup/production-environment/tools/kubeadm/create-cluster-kubeadm).

On each worker node where you will configure swap use, you need: * `fallocate` * `mkswap` * `swapon`

* For encrypted swap space (recommended), you also need: * `cryptsetup`

## Install a swap-enabled cluster with kubeadm

### Create a swap file and turn swap on

If swap is not enabled, there's a need to provision swap on the node. The following sections demonstrate creating 4GiB of swap, both in the encrypted and unencrypted case.

An encrypted swap file can be set up as follows. Bear in mind that this example uses the `cryptsetup` binary (which is available on most Linux distributions).

```bash # Allocate storage and restrict access fallocate --length 4GiB /swapfile chmod 600 /swapfile

# Create an encrypted device backed by the allocated storage cryptsetup --type plain --cipher aes-xts-plain64 --key-size 256 -d /dev/urandom open /swapfile cryptswap

# Format the swap space mkswap /dev/mapper/cryptswap

# Activate the swap space for paging swapon /dev/mapper/cryptswap ```

An unencrypted swap file can be set up as follows.

```bash # Allocate storage and restrict access fallocate --length 4GiB /swapfile chmod 600 /swapfile

# Format the swap space mkswap /swapfile

# Activate the swap space for paging swapon /swapfile ```

#### Verify that swap is enabled

Swap can be verified to be enabled with both `swapon -s` command or the `free` command.

Using `swapon -s`: ``` Filename Type Size Used Priority /dev/dm-0 partition 4194300 0 -2 ```

Using `free -h`: ``` total used free shared buff/cache available Mem: 3.8Gi 1.3Gi 249Mi 25Mi 2.5Gi 2.5Gi Swap: 4.0Gi 0B 4.0Gi ```

#### Enable swap on boot

After setting up swap, to start the swap file at boot time, you typically either set up a systemd unit to activate (encrypted) swap, or you add a line similar to `/swapfile swap swap defaults 0 0` into `/etc/fstab`.

Using systemd for swap activation allows the system to delay kubelet start until swap is available, if that is something you want to ensure. In a similar way, using systemd allows your server to leave swap active until kubelet (and, typically, your container runtime) have shut down.

### Set up kubelet configuration

After enabling swap on the node, kubelet needs to be configured to use it. You need to select a [swap behavior](/docs/reference/node/swap-behavior/) for this node. You'll configure _LimitedSwap_ behavior for this tutorial.

Find and edit the kubelet configuration file, and:

set `failSwapOn` to false
set `memorySwap.swapBehavior` to LimitedSwap

```yaml # this fragment goes into the kubelet's configuration file failSwapOn: false memorySwap: swapBehavior: LimitedSwap ```

In order for these configurations to take effect, kubelet needs to be restarted. Typically you do that by running: ```shell systemctl restart kubelet.service ```

You should find that the kubelet is now healthy, and that you can run Pods that use swap memory as needed.

Sources

tutorials/cluster-management/provision-swap-memory.md · doc — “Configuring swap memory on Kubernetes nodes”

Related (6)

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part_of {{% heading "prerequisites" %}} — describes conf=1

part_of Install a swap-enabled cluster with kubeadm — describes conf=1

part_of Create a swap file and turn swap on — describes conf=1

part_of Set up kubelet configuration — describes conf=1

api_for Node — documents API object conf=1

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