k3s/cluster/juju/layers/kubernetes-worker

Kubernetes Worker

Usage

This charm deploys a container runtime, and additionally stands up the Kubernetes worker applications: kubelet, and kube-proxy.

In order for this charm to be useful, it should be deployed with its companion charm kubernetes-master and linked with an SDN-Plugin.

This charm has also been bundled up for your convenience so you can skip the above steps, and deploy it with a single command:

juju deploy canonical-kubernetes

For more information about Canonical Kubernetes consult the bundle README.md file.

Scale out

To add additional compute capacity to your Kubernetes workers, you may juju add-unit scale the cluster of applications. They will automatically join any related kubernetes-master, and enlist themselves as ready once the deployment is complete.

Snap Configuration

The kubernetes resources used by this charm are snap packages. When not specified during deployment, these resources come from the public store. By default, the snapd daemon will refresh all snaps installed from the store four (4) times per day. A charm configuration option is provided for operators to control this refresh frequency.

NOTE: this is a global configuration option and will affect the refresh time for all snaps installed on a system.

Examples:

## refresh kubernetes-worker snaps every tuesday
juju config kubernetes-worker snapd_refresh="tue"

## refresh snaps at 11pm on the last (5th) friday of the month
juju config kubernetes-worker snapd_refresh="fri5,23:00"

## delay the refresh as long as possible
juju config kubernetes-worker snapd_refresh="max"

## use the system default refresh timer
juju config kubernetes-worker snapd_refresh=""

For more information on the possible values for snapd_refresh, see the refresh.timer section in the system options documentation.

Operational actions

The kubernetes-worker charm supports the following Operational Actions:

Pause

Pausing the workload enables administrators to both drain and cordon a unit for maintenance.

Resume

Resuming the workload will uncordon a paused unit. Workloads will automatically migrate unless otherwise directed via their application declaration.

Private registry

With the "registry" action that is part for the kubernetes-worker charm, you can very easily create a private docker registry, with authentication, and available over TLS. Please note that the registry deployed with the action is not HA, and uses storage tied to the kubernetes node where the pod is running. So if the registry pod changes is migrated from one node to another for whatever reason, you will need to re-publish the images.

Example usage

Create the relevant authentication files. Let's say you want user userA to authenticate with the password passwordA. Then you'll do :

echo -n "userA:passwordA" > htpasswd-plain
htpasswd -c -b -B htpasswd userA passwordA

(the htpasswd program comes with the apache2-utils package)

Supposing your registry will be reachable at myregistry.company.com, and that you already have your TLS key in the registry.key file, and your TLS certificate (with myregistry.company.com as Common Name) in the registry.crt file, you would then run :

juju run-action kubernetes-worker/0 registry domain=myregistry.company.com htpasswd="$(base64 -w0 htpasswd)" htpasswd-plain="$(base64 -w0 htpasswd-plain)" tlscert="$(base64 -w0 registry.crt)" tlskey="$(base64 -w0 registry.key)" ingress=true

If you then decide that you want do delete the registry, just run :

juju run-action kubernetes-worker/0 registry delete=true ingress=true

Known Limitations

Kubernetes workers currently only support 'phaux' HA scenarios. Even when configured with an HA cluster string, they will only ever contact the first unit in the cluster map. To enable a proper HA story, kubernetes-worker units are encouraged to proxy through a kubeapi-load-balancer application. This enables a HA deployment without the need to re-render configuration and disrupt the worker services.

External access to pods must be performed through a Kubernetes Ingress Resource.

When using NodePort type networking, there is no automation in exposing the ports selected by kubernetes or chosen by the user. They will need to be opened manually and can be performed across an entire worker pool.

If your NodePort service port selected is 30510 you can open this across all members of a worker pool named kubernetes-worker like so:

juju run --application kubernetes-worker open-port 30510/tcp

Don't forget to expose the kubernetes-worker application if its not already exposed, as this can cause confusion once the port has been opened and the service is not reachable.

Note: When debugging connection issues with NodePort services, its important to first check the kube-proxy service on the worker units. If kube-proxy is not running, the associated port-mapping will not be configured in the iptables rulechains.

If you need to close the NodePort once a workload has been terminated, you can follow the same steps inversely.

juju run --application kubernetes-worker close-port 30510