Kubernetes-worker charm

This charm deploys a container runtime and 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 and a container runtime such as containerd.

This charm is part of the Charmed Kubernetes bundle bundle which can be deployed with a single command::

juju deploy charmed-kubernetes

For more information about Charmed Kubernetes see the overview documentation

Scale out

To add additional compute capacity to your Kubernetes workers, you may juju add-unit kubernetes-worker to scale the cluster. The new units 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.

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, see the snap documentation.

Configuration

This charm supports some configuration options to set up a Kubernetes cluster that works in your environment, detailed in the section below.

For some specific Kubernetes service configuration tasks, please also see the section on configuring K8s services. Please also see the kubernetes-master charm configuration for other settings relating to Kubernetes services.

ingress-ssl-chain-completion

Description:

Enable chain completion for TLS certificates used by the nginx ingress controller. Set this to true if you would like the ingress controller to attempt auto-retrieval of intermediate certificates. The default (false) is recommended for all production kubernetes installations, and any environment which does not have outbound Internet access.

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kubelet-extra-args

Description:

Space separated list of flags and key=value pairs that will be passed as arguments to kubelet. For example a value like this:

  runtime-config=batch/v2alpha1=true profiling=true

will result in kubelet being run with the following options:

  --runtime-config=batch/v2alpha1=true --profiling=true

Note: As of Kubernetes 1.10.x, many of Kubelet’s args have been deprecated, and can be set with kubelet-extra-config instead.

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kubelet-extra-config

Description:

Extra configuration to be passed to kubelet. Any values specified in this config will be merged into a KubeletConfiguration file that is passed to the kubelet service via the –config flag. This can be used to override values provided by the charm.

Requires Kubernetes 1.10+.

The value for this config must be a YAML mapping that can be safely merged with a KubeletConfiguration file. For example:

  {evictionHard: {memory.available: 200Mi}}

For more information about KubeletConfiguration, see upstream docs: https://kubernetes.io/docs/tasks/administer-cluster/kubelet-config-file/

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nagios_context

Description:

Used by the nrpe subordinate charms. A string that will be prepended to instance name to set the host name in nagios. So for instance the hostname would be something like:

    juju-myservice-0

If you’re running multiple environments with the same services in them this allows you to differentiate between them.

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proxy-extra-args

Description:

Space separated list of flags and key=value pairs that will be passed as arguments to kube-proxy. For example a value like this:

  runtime-config=batch/v2alpha1=true profiling=true

will result in kube-apiserver being run with the following options: –runtime-config=batch/v2alpha1=true –profiling=true

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snapd_refresh

Description:

How often snapd handles updates for installed snaps. Setting an empty string will check 4x per day. Set to “max” to delay the refresh as long as possible. You may also set a custom string as described in the ‘refresh.timer’ section here: https://forum.snapcraft.io/t/system-options/87

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sysctl

Default:

{ net.ipv4.conf.all.forwarding : 1, net.ipv4.neigh.default.gc_thresh1 : 128, net.ipv4.neigh.default.gc_thresh2 : 28672, net.ipv4.neigh.default.gc_thresh3 : 32768, net.ipv6.neigh.default.gc_thresh1 : 128, net.ipv6.neigh.default.gc_thresh2 : 28672, net.ipv6.neigh.default.gc_thresh3 : 32768, fs.inotify.max_user_instances : 8192, fs.inotify.max_user_watches: 1048576 }

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Description:

YAML formatted associative array of sysctl values, e.g.: ‘{kernel.pid_max : 4194303 }’. Note that kube-proxy handles the conntrack settings. The proper way to alter them is to use the proxy-extra-args config to set them, e.g.:

  juju config kubernetes-master proxy-extra-args="conntrack-min=1000000 conntrack-max-per-core=250000"
  juju config kubernetes-worker proxy-extra-args="conntrack-min=1000000 conntrack-max-per-core=250000"

The proxy-extra-args conntrack-min and conntrack-max-per-core can be set to 0 to ignore kube-proxy’s settings and use the sysctl settings instead. Note the fundamental difference between the setting of conntrack-max-per-core vs nf_conntrack_max.

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Configuring K8s services

IPVS (IP Virtual Server)

This requires configuration of both the kubernetes-master and kubernetes-worker charms. Please see the configuration section on the kubernetes-master page.

Configuring kubelet

Each worker runs the node agent, kubelet with a set of arguments and configuration set by this charm. In some cases it may be desirable to add options or arguments, for which the charm provides two mechanisms

kubelet-extra-args for command line options. kubelet-extra-config for configuration.

The definitive reference for kubelet is the upstream documentation.

HugePages

HugePages are a standard memory management feature of the Linux kernel to decrease overhead for processes which consume large amounts of memory.

Kubernetes includes support for using HugePages with pods (see the upstream documentation).

To use HugePages in your pods with Charmed Kubernetes, it is necessary to update the configuration for the workers:

1. Fetch the current ‘sysctl’ configuration from the worker:

   juju config kubernetes-worker sysctl
   

   This should return a string of config options, e.g.:

   { net.ipv4.conf.all.forwarding : 1, net.ipv4.neigh.default.gc_thresh1 : 128, net.ipv4.neigh.default.gc_thresh2 : 28672, net.ipv4.neigh.default.gc_thresh3 : 32768, net.ipv6.neigh.default.gc_thresh1 : 128, net.ipv6.neigh.default.gc_thresh2 : 28672, net.ipv6.neigh.default.gc_thresh3 : 32768, fs.inotify.max_user_instances : 8192, fs.inotify.max_user_watches: 1048576 }
   

2. The config option for HugePages is vm.nr_hugepages. To add this configuration, you should append it to the string and set the whole configuration. For example, for 100 2Mi pages:

   juju config kubernetes-worker sysctl="{ net.ipv4.conf.all.forwarding : 1, net.ipv4.neigh.default.gc_thresh1 : 128, net.ipv4.neigh.default.gc_thresh2 : 28672, net.ipv4.neigh.default.gc_thresh3 : 32768, net.ipv6.neigh.default.gc_thresh1 : 128, net.ipv6.neigh.default.gc_thresh2 : 28672, net.ipv6.neigh.default.gc_thresh3 : 32768, fs.inotify.max_user_instances : 8192, fs.inotify.max_user_watches: 1048576, vm.nr_hugepages: 100}"
   

3. HugePages can now be consumed via container level resource requirements using the resource name hugepages-<size>.

   For example:

   apiVersion: v1
   kind: Pod
   metadata:
     name: hugepages-test
   spec:
     containers:
     - image: ubuntu:latest
       command:
       - sleep
       - inf
       name: example
       volumeMounts:
       - mountPath: /hugepages
         name: hugepage
       resources:
         limits:
           hugepages-2Mi: 100Mi
           memory: 100Mi
         requests:
           memory: 100Mi
     volumes:
     - name: hugepage
       emptyDir:
         medium: HugePages
   

   Huge page usage in a namespace can be managed with ResourceQuota, similar to other compute resources.

4. To verify, you can exec into the pod and check the /proc/meminfo.

   kubectl exec hugepage-test cat /proc/meminfo | grep HugePages_
   

Actions

You can run an action with the following

juju run-action kubernetes-worker ACTION [parameters] [--wait]

apply

config

release

delete

replicas

delete-local-data

force

delete

domain

htpasswd

htpasswd-plain

ingress

tlscert

tlskey