Container runtimes

From 1.15 onwards, Charmed Kubernetes uses containerd as part of a pluggable architecture for container runtimes, instead of directly using Docker only. This change has been demonstrated to increase performance, and also provides scope for using different runtimes on a case-by case basis.

However, it is also possible to use Docker for running containers as in previous versions of Charmed Kubernetes.

Configuring containerd

Settings which require additional explanation are described below.

Name Type Default Value Description
custom_registries: json '[]' Setting this config allows images to be pulled from registries requiring auth. See below.
enable-cgroups bool False WARNING changing this option will reboot the host - see notes.
extra-packages string "" Space separated list of extra deb packages to install.
gpu-driver string 'auto' Override GPU driver installation. Options are "auto", "nvidia", "none".
http_proxy string "" URL to use for HTTP_PROXY: useful in egress-filtered environments where a proxy is the only option for accessing the registry to pull images.
https_proxy string "" URL to use for HTTP_PROXY: useful in egress-filtered environments where a proxy is the only option for accessing the registry to pull images.
install_keys string "" List of signing keys for install_sources package sources - see notes
install_sources string "" List of extra apt sources - See notes
no_proxy string "" Comma-separated list of destinations (either domain names or IP addresses) which should be accessed directly, rather than through the proxy defined in http_proxy or https_proxy. Must be less than 2023 characters long.
package_status string 'install' The status of service-affecting packages will be set to this value in the dpkg database. Valid values are "install" and "hold".
runtime string 'auto' Set a custom containerd runtime. Set "auto" to select based on hardware.
shim string 'containerd-shim' Set a custom containerd shim.

Checking the current configuration

To check the current configuration settings for containerd, run the command:

juju config containerd

Setting a config option

To set an option, simply run the config command with and additional <key>=<value> argument. For example, to explicitly turn off the nvidia driver:

juju config containerd gpu_driver=none

Migrating to containerd

If you have upgraded to Charmed Kubernetes version 1.15, you can transition to using containerd by following the steps outlined in this section of the upgrade notes.

Using Docker

Although the default set up for Charmed Kubernetes from version 1.15 is to use containerd to provide the container runtime, it is also possible to run workers specifically using Docker. This is done by adding the Docker charm to your cluster and deploying Docker-based workers:

juju deploy cs:~containers/kubernetes-worker kubernetes-worker-docker
juju deploy cs:~containers/docker
juju relate docker kubernetes-worker-docker