Description

A minimal two-machine Kubernetes cluster, appropriate for development.

Kubernetes Core Bundle

Overview

This is a minimal Kubernetes cluster composed of the following components and features:

  • Kubernetes (automated deployment, operations, and scaling)
    • Two-node Kubernetes cluster with one master node and one worker node.
    • TLS used for communication between nodes for security.
    • A CNI plugin (Flannel)
    • Optional Ingress Controller (on worker)
    • Optional Dashboard addon (on master) including Heapster for cluster monitoring
  • EasyRSA
    • Performs the role of a certificate authority serving self signed certificates
      to the requesting units of the cluster.
  • Etcd (distributed key value store)
    • One node for basic functionality.

This bundle is suitable for development and testing purposes. For a more robust, scaled-out cluster, deploy the
canonical-kubernetes bundle via conjure-up canonical-kubernetes.

Usage

Installation has been automated via conjure-up:

sudo snap install conjure-up --classic
conjure-up kubernetes-core

Conjure-up will prompt you for deployment options (AWS, GCE, Azure, etc.) and credentials.

Proxy configuration

If you are operating behind a proxy (i.e., your charms are running in a
limited-egress environment and can not reach IP addresses external to their
network), you will need to configure your model appropriately before deploying
the Kubernetes bundle.

First, configure your model's http-proxy and https-proxy settings with your
proxy (here we use squid.internal:3128 as an example):

$ juju model-config http-proxy=http://squid.internal:3128 https-proxy=https://squid.internal:3128

Because services often need to reach machines on their own network (including
themselves), you will also need to add localhost to the no-proxy model
configuration setting, along with any internal subnets you're using. The
following example includes two subnets:

$ juju model-config no-proxy=localhost,10.5.5.0/24,10.246.64.0/21

After deploying the bundle, you need to configure the kubernetes-worker charm
to use your proxy:

$ juju config kubernetes-worker http_proxy=http://squid.internal:3128 https_proxy=https://squid.internal:3128

Alternate deployment methods

Deploying with Juju directly

juju deploy kubernetes-core

Note: If you're deploying on lxd, use conjure-up instead, as described
above. It configures your lxd profile to support running Kubernetes on lxd.

Note: If you're operating behind a proxy, remember to set the kubernetes-worker
proxy configuration options as described in the Proxy configuration section
above.

This bundle exposes the kubernetes-worker charm by default. This means that
it is accessible through its public address.

If you would like to remove external access to the worker node, unexpose it:

juju unexpose kubernetes-worker

To get the status of the deployment, run juju status. For constant updates,
combine it with the watch command:

watch -c juju status --color

Using with your own resources

In order to support restricted-network deployments, the charms in this bundle
support
juju resources.

This allows you to juju attach the resources built for the architecture of
your cloud.

juju attach kubernetes-master kubectl=/path/to/kubectl.snap
juju attach kubernetes-master kube-apiserver=/path/to/kube-apiserver.snap
juju attach kubernetes-master kube-controller-manager=/path/to/kube-controller-manager.snap
juju attach kubernetes-master kube-scheduler=/path/to/kube-scheduler.snap
juju attach kubernetes-master cdk-addons=/path/to/cdk-addons.snap

juju attach kubernetes-worker kubectl=/path/to/kubectl.snap
juju attach kubernetes-worker kubelet=/path/to/kubelet.snap
juju attach kubernetes-worker kube-proxy=/path/to/kube-proxy.snap
juju attach kubernetes-worker cni=/path/to/cni.tgz

Using a specific Kubernetes version

You can select a specific version or series of Kubernetes by configuring the charms
to use a specific snap channel. For example, to use the 1.6 series:

juju config kubernetes-master channel=1.6/stable
juju config kubernetes-worker channel=1.6/stable

After changing the channel, you'll need to manually execute the upgrade action
on each kubernetes-worker unit, e.g.:

juju run-action kubernetes-worker/0 upgrade
juju run-action kubernetes-worker/1 upgrade
juju run-action kubernetes-worker/2 upgrade
...

By default, the channel is set to stable on the current minor version of Kubernetes, for example, 1.6/stable. This means your cluster will receive automatic upgrades for new patch releases (e.g. 1.6.2 -> 1.6.3), but not for new minor versions (e.g. 1.6.3 -> 1.7). To upgrade to a new minor version, configure the channel manually as described above.

Interacting with the Kubernetes cluster

After the cluster is deployed you may assume control over the Kubernetes cluster
from any kubernetes-master or kubernetes-worker node.

To download the credentials and client application to your local workstation:

Create the kubectl config directory.

mkdir -p ~/.kube

Copy the kubeconfig to the default location.

juju scp kubernetes-master/0:config ~/.kube/config

Install kubectl locally.

snap install kubectl --classic

Query the cluster.

kubectl cluster-info

Accessing the Kubernetes Dashboard

The Kubernetes dashboard addon is installed by default, along with Heapster,
Grafana and InfluxDB for cluster monitoring. The dashboard addons can be
enabled or disabled by setting the enable-dashboard-addons config on the
kubernetes-master application:

juju config kubernetes-master enable-dashboard-addons=true

To access the dashboard, you may establish a secure tunnel to your cluster with
the following command:

kubectl proxy

By default, this establishes a proxy running on your local machine and the
kubernetes-master unit. To reach the Kubernetes dashboard, visit
http://localhost:8001/ui

Control the cluster

kubectl is the command line utility to interact with a Kubernetes cluster.

Minimal getting started

To check the state of the cluster:

kubectl cluster-info

List all nodes in the cluster:

kubectl get nodes

Now you can run pods inside the Kubernetes cluster:

kubectl create -f example.yaml

List all pods in the cluster:

kubectl get pods

List all services in the cluster:

kubectl get services

For expanded information on kubectl beyond what this README provides, please
see the
kubectl overview
which contains practical examples and an API reference.

Additionally if you need to manage multiple clusters, there is more information
about configuring kubectl in the
kubectl config guide

Using Ingress

The kubernetes-worker charm supports deploying an NGINX ingress controller.
Ingress allows access from the Internet to containers running web
services inside the cluster.

First allow the Internet access to the kubernetes-worker charm with the
following Juju command:

juju expose kubernetes-worker

In Kubernetes, workloads are declared using pod, service, and ingress
definitions. An ingress controller is provided to you by default and deployed into
the
default namespace of the
cluster. If one is not available, you may deploy it with:

juju config kubernetes-worker ingress=true

Ingress resources are DNS mappings to your containers, routed through
endpoints.

As an example for users unfamiliar with Kubernetes, we packaged an action to
both deploy an example and clean itself up.

To deploy 5 replicas of the microbot web application inside the Kubernetes
cluster run the following command:

juju run-action kubernetes-worker/0 microbot replicas=5

This action performs the following steps:

  • It creates a deployment titled 'microbots' composed of 5 replicas defined
    during the run of the action. It also creates a service named 'microbots'
    which binds an 'endpoint', using all 5 of the 'microbots' pods.

  • Finally, it will create an ingress resource, which points at a
    xip.io domain to simulate a proper DNS service.

Running the packaged simulation

Run a Juju action to create the example microbot web application:

$ juju run-action kubernetes-worker/0 microbot replicas=3
Action queued with id: db7cc72b-5f35-4a4d-877c-284c4b776eb8

$ juju show-action-output db7cc72b-5f35-4a4d-877c-284c4b776eb8
results:
  address: microbot.104.198.77.197.xip.io
status: completed
timing:
  completed: 2016-09-26 20:42:42 +0000 UTC
  enqueued: 2016-09-26 20:42:39 +0000 UTC
  started: 2016-09-26 20:42:41 +0000 UTC

Note: Your FQDN will be different and contain the address of the cloud
instance.

At this point, you can inspect the cluster to observe the workload coming online.

List the pods

$ kubectl get pods
NAME                             READY     STATUS    RESTARTS   AGE
default-http-backend-kh1dt       1/1       Running   0          1h
microbot-1855935831-58shp        1/1       Running   0          1h
microbot-1855935831-9d16f        1/1       Running   0          1h
microbot-1855935831-l5rt8        1/1       Running   0          1h
nginx-ingress-controller-hv5c2   1/1       Running   0          1h

List the services and endpoints

$ kubectl get services,endpoints
NAME                       CLUSTER-IP    EXTERNAL-IP   PORT(S)   AGE
svc/default-http-backend   10.1.225.82   <none>        80/TCP    1h
svc/kubernetes             10.1.0.1      <none>        443/TCP   1h
svc/microbot               10.1.44.173   <none>        80/TCP    1h
NAME                      ENDPOINTS                               AGE
ep/default-http-backend   10.1.68.2:80                            1h
ep/kubernetes             172.31.31.139:6443                      1h
ep/microbot               10.1.20.3:80,10.1.68.3:80,10.1.7.4:80   1h

List the ingress resources

$ kubectl get ingress
NAME               HOSTS                          ADDRESS         PORTS     AGE
microbot-ingress   microbot.52.38.62.235.xip.io   172.31.26.109   80        1h

When all the pods are listed as Running, you are ready to visit the address listed in the HOSTS column of the ingress listing.

Note: It is normal to see a 502/503 error during initial application deployment.

As you refresh the page, you will be greeted with a microbot web page, serving
from one of the microbot replica pods. Refreshing will show you another
microbot with a different hostname as the requests are load-balanced across
the replicas.

Clean up microbot

There is also an action to clean up the microbot applications. When you are
done using the microbot application you can delete the pods with
one Juju action:

juju run-action kubernetes-worker/0 microbot delete=true

If you no longer need Internet access to your workers, remember to unexpose the
kubernetes-worker charm:

juju unexpose kubernetes-worker

To learn more about
Kubernetes Ingress
and how to configure the Ingress Controller beyond defaults (such as TLS and
websocket support) view the
nginx-ingress-controller
project on github.

Scale-out Usage

Scaling kubernetes-worker

The kubernetes-worker nodes are the load-bearing units of a Kubernetes cluster.

By default, pods are automatically spread across the kubernetes-worker units
that you have deployed.

To add more kubernetes-worker units to the cluster:

juju add-unit kubernetes-worker

or specify machine constraints to create larger nodes:

juju add-unit kubernetes-worker --constraints "cpu-cores=8 mem=32G"

Refer to the
machine constraints documentation
for other machine constraints that might be useful for the kubernetes-worker units.

Scaling Etcd

Etcd is the key-value store for the Kubernetes cluster. The bundle
defaults to one instance of etcd in this cluster.

For reliability and scalability, use at least 3 etcd nodes.
To add two more nodes:

juju add-unit etcd -n 2

The CoreOS etcd documentation has a chart for the
optimal cluster size
to determine fault tolerance.

Known Limitations and Issues

The following are known issues and limitations with the bundle and charm code:

  • Destroying the the easyrsa charm will result in loss of public key
    infrastructure (PKI).

  • Deployment locally on LXD will require the use of conjure-up to tune
    settings on the host's LXD installation to support Docker and other
    components.

  • If resources fail to download during initial deployment for any reason, you
    will need to download and install them manually. For example, if
    kubernetes-master is missing its resources, download them from the resources
    section of the sidebar here
    and install them by running, for example:

juju attach kubernetes-master kube-apiserver=/path/to/snap.

You can find resources for the kubernetes-core charms here:

Kubernetes details

Flannel

Flannel is a virtual network that gives a subnet to each host for use with
container runtimes.

Configuration

iface The interface to configure the flannel SDN binding. If this value is
empty string or undefined the code will attempt to find the default network
adapter similar to the following command:

route | grep default | head -n 1 | awk {'print $8'}

cidr The network range to configure the flannel SDN to declare when
establishing networking setup with etcd. Ensure this network range is not active
on the vlan you're deploying to, as it will cause collisions and odd behavior
if care is not taken when selecting a good CIDR range to assign to flannel.

Known Limitations

This subordinate does not support being co-located with other deployments of
the flannel subordinate (to gain 2 vlans on a single application). If you
require this support please file a bug.

This subordinate also leverages juju-resources, so it is currently only available
on juju 2.0+ controllers.

Further information