Container runtimes

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

Upstream support for the Docker container runtime was removed in the 1.24 release. Thus, the docker subordinate charm will no longer function from Charmed Kubernetes 1.24 onwards.

Configuring containerd

Settings which require additional explanation are described below.

name	type	Default	Description
custom_registries	string	[]	See notes
disable-juju-proxy	boolean	False	Ignore juju-http(s) proxy settings on this charm. If set to true, all juju https proxy settings will be ignored
enable-cgroups	boolean	False	Enable GRUB cgroup overrides cgroup_enable=memory swapaccount=1. WARNING changing this option will reboot the host - use with caution on production services.
gpu_driver	string	auto	Override GPU driver installation. Options are "auto", "nvidia", "none".
http_proxy	string		URL to use for HTTP_PROXY to be used by Containerd. 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 HTTPS_PROXY to be used by Containerd. Useful in egress-filtered environments where a proxy is the only option for accessing the registry to pull images.
no_proxy	string		See notes
runtime	string	auto	Set a custom containerd runtime. Set "auto" to select based on hardware.
shim	string	containerd-shim	Set a custom containerd shim.

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custom_registries

Description:

Registry credentials. Setting this config allows Kubelet to pull images from registries where auth is required.

The value for this config must be a JSON array of credential objects, like this: [{"url": "https://my.registry:port", "username": "user", "password": "pass"}]

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no_proxy

Description:

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.

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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 an additional <key>=<value> argument. For example, to explicitly turn off the nvidia driver:

juju config containerd gpu_driver=none

Migrating to containerd

If you are upgrading from a version of Charmed Kubernetes that uses the docker subordinate charm for the container runtime, transition to containerd by following the steps outlined in this section of the upgrade notes.