Kubernetes is an open source system for managing application containers across multiple hosts. This version of Kubernetes uses Docker to package, instantiate and run containerized applications.
This charm is an encapsulation of the
Running Kubernetes locally via
Docker
document. The released hyperkube image (gcr.io/google_containers/hyperkube)
is currently pulled from a Google owned container repository
repository. For this charm to
work it will need access to the repository to docker pull the images.
This charm was built from other charm layers using the reactive framework. The
layer:docker is the base layer. For more information please read Getting
Started Developing charms
The kubernetes charms require a relation to a distributed key value store (ETCD) which Kubernetes uses for persistent storage of all of its REST API objects.
juju deploy etcd
juju deploy kubernetes
juju add-relation kubernetes etcdFor your convenience this charm supports some configuration options to set up a Kubernetes cluster that works in your environment:
version: Set the version of the Kubernetes containers to deploy. The version string must be in the following format "v#.#.#" where the numbers match with the kubernetes release labels of the kubernetes github project. Changing the version causes the all the Kubernetes containers to be restarted.
cidr: Set the IP range for the Kubernetes cluster. eg: 10.1.0.0/16
dns_domain: Set the DNS domain for the Kubernetes cluster.
The kubernetes charm is built to handle multiple storage devices if the cloud provider works with Juju storage.
The 16.04 (xenial) release introduced ZFS to Ubuntu. The xenial charm can use ZFS witha raidz pool. A raidz pool distributes parity along with the data (similar to a raid5 pool) and can suffer the loss of one drive while still retaining data. The raidz pool requires a minimum of 3 disks, but will accept more if they are provided.
You can add storage to the kubernetes charm in increments of 3 or greater:
juju add-storage kubernetes/0 disk-pool=ebs,3,1GNote: Due to a limitation of raidz you can not add individual disks to an existing pool. Should you need to expand the storage of the raidz pool, the additional add-storage commands must be the same number of disks as the original command. At this point the charm will have two raidz pools added together, both of which could handle the loss of one disk each.
The storage code handles the addition of devices to the charm and when it
recieves three disks creates a raidz pool that is mounted at the /srv/kubernetes
directory by default. If you need the storage in another location you must
change the mount-point value in layer.yaml before the charms is deployed.
To avoid data loss you must attach the storage before making the connection to the etcd cluster.
While this charm is meant to be a top layer, it can be used to build other solutions. This charm sets or removes states from the reactive framework that other layers could react appropriately. The states that other layers would be interested in are as follows:
kubelet.available - The hyperkube container has been run with the kubelet service and configuration that started the apiserver, controller-manager and scheduler containers.
proxy.available - The hyperkube container has been run with the proxy service and configuration that handles Kubernetes networking.
kubectl.package.created - Indicates the availability of the kubectl
application along with the configuration needed to contact the cluster
securely. You will need to download the /home/ubuntu/kubectl_package.tar.gz
from the kubernetes leader unit to your machine so you can control the cluster.
kubedns.available - Indicates when the Domain Name System (DNS) for the cluster is operational.