Kubernetes is an open source system for managing application containers across a cluster of hosts. The Kubernetes project was started by Google in 2014, combining the experience of running production workloads combined with best practices from the community.
The Kubernetes project defines some new terms that may be unfamiliar to users or operators. For more information please refer to the concept guide in the getting started guide.
This charm is an encapsulation of the Kubernetes master processes and the operations to run on any cloud for the entire lifecycle of the cluster.
This charm is built from other charm layers using the Juju reactive framework. The other layers focus on specific subset of operations making this layer specific to operations of Kubernetes master processes.
This charm is not fully functional when deployed by itself. It requires other charms to model a complete Kubernetes cluster. A Kubernetes cluster needs a distributed key value store such as Etcd and the kubernetes-worker charm which delivers the Kubernetes node services. A cluster requires a Software Defined Network (SDN), a Container Runtime such as containerd, and Transport Layer Security (TLS) so the components in a cluster communicate securely.
Please take a look at the Canonical Distribution of Kubernetes or the Kubernetes core bundles for examples of complete models of Kubernetes clusters.
The kubernetes-master charm takes advantage of the Juju Resources feature to deliver the Kubernetes software.
In deployments on public clouds the Charm Store provides the resource to the charm automatically with no user intervention. Some environments with strict firewall rules may not be able to contact the Charm Store. In these network restricted environments the resource can be uploaded to the model by the Juju operator.
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-master snaps every tuesday
juju config kubernetes-master snapd_refresh="tue"
## refresh snaps at 11pm on the last (5th) friday of the month
juju config kubernetes-master snapd_refresh="fri5,23:00"
## delay the refresh as long as possible
juju config kubernetes-master snapd_refresh="max"
## use the system default refresh timer
juju config kubernetes-master snapd_refresh=""For more information on the possible values for snapd_refresh, see the
refresh.timer section in the system options documentation.
This charm supports some configuration options to set up a Kubernetes cluster that works in your environment:
Comma separated authorization modes. For example, enable RBAC and Node authorization:
juju config kubernetes-master authorization-mode="RBAC,Node"The domain name to use for the Kubernetes cluster for DNS.
Enables the installation of Kubernetes dashboard, Heapster, Grafana, and InfluxDB.
The DNS add-on allows the pods to have a DNS names in addition to IP addresses. The Kubernetes cluster DNS server (based off the SkyDNS library) supports forward lookups (A records), service lookups (SRV records) and reverse IP address lookups (PTR records). More information about the DNS can be obtained from the Kubernetes DNS admin guide.
The kubernetes-master charm models a few one time operations called Juju actions that can be run by Juju users.
This action creates RADOS Block Device (RBD) in Ceph and defines a Persistent Volume in Kubernetes so the containers can use durable storage. This action requires a relation to the ceph-mon charm before it can create the volume.
This action restarts the master processes kube-apiserver,
kube-controller-manager, and kube-scheduler when the user needs a restart.
The kubernetes-master charm is free and open source operations created by the containers team at Canonical.
Canonical also offers enterprise support and customization services. Please refer to the Kubernetes product page for more details.