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Disk Limit in a Docker-based K8s Cluster

Docker provides configuration options to limit the disk space that a container can use. This limit affects both the image and the container's filesystem, with a default value of 10G. This article will guide you on how to configure parameters to change this value when deploying a cluster.

Prerequisites

According to the Docker official documentation on overlay2-options, before configuring Docker overlay2.size, you need to adjust the filesystem type to xfs in the operating system.

  • The cluster runtime is Docker.
  • The node's operating system filesystem type is xfs.

Additionally, this procedure uses CentOS 7 as an example. The basic information of the node is as follows:

$ cat /etc/os-release
NAME="CentOS Linux"
VERSION="7 (Core)"
ID="centos"
ID_LIKE="rhel fedora"
VERSION_ID="7"
PRETTY_NAME="CentOS Linux 7 (Core)"
ANSI_COLOR="0;31"
CPE_NAME="cpe:/o:centos:centos:7"
HOME_URL="https://www.centos.org/"
BUG_REPORT_URL="https://bugs.centos.org/"

CENTOS_MANTISBT_PROJECT="CentOS-7"
CENTOS_MANTISBT_PROJECT_VERSION="7"
REDHAT_SUPPORT_PRODUCT="centos"
REDHAT_SUPPORT_PRODUCT_VERSION="7"

$ uname -a
Linux localhost.localdomain 3.10.0-957.el7.x86_64 # (1)!
  1. SMP Thu Nov 8 23:39:32 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

Operation Guide

  • Refer to the container management Create Cluster documentation. After filling in other information, navigate to the Advanced Configuration module.

  • In the Advanced Configuration interface, add the following line in the custom parameters:

    docker_storage_options: -s overlay2 --storage-opt overlay2.size=1G

    image

    This parameter limits the maximum disk usage of a single Docker container to 1G. Any write operations beyond 1G will be denied.

Validation

After the cluster deployment is complete, verify whether the container disk usage limit is effective.

  • Create a test container on the cluster node:

    docker run --name test -d busybox:latest sleep infinity

  • Enter the container and test the disk usage limit with a large file:

    docker exec -it test sh

dd if=/dev/zero of=a bs=100M count=10

  • The expected behavior is that the creation of the initial 100M file a will succeed. However, when attempting to create another 100M file b, an error "No space left on device" will occur, indicating that the disk limit is in effect, as shown below:

    image

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