Using Kubernetes with Juju

Kubernetes (“K8s”) provides a flexible architecture for cloud-native applications at scale. We believe that Juju is the simplest way to manage a multi-container workloads on K8s. This guide takes you through the registration steps necessary to connect the two systems.

What is Juju?: Juju is the simplest DevOps tool for managing digital services built with inter-related applications. If you are unfamiliar with Juju, then we recommend following our Getting Started with Juju tutorial.

Need a Kubernetes cluster for experimentation?: Install MicroK8s to create a local Kubernetes cluster with zero effort.

Running Kubernetes workloads

To run workloads on Kubernetes with Juju, a small number of registration steps are required:

  1. Obtain a Kubernetes cluster
  2. Register the cluster with Juju
  3. Create a Juju controller
  4. Register storage resources

You’re now ready to deploy cloud-native workloads with charms:

  1. Add a model
  2. Deploy workloads

Obtain a Kubernetes cluster

There are many ways to obtain a Kubernetes cluster. If you are unsure which option to choose, then you should install MicroK8s.

Use Case Recommended Action(s)
Local development, testing and experimentation Install MicroK8s
Multi-node testing/production on a private cloud Install Charmed Kubernetes
Multi-node testing/production on the public cloud Install Charmed Kubernetes with the relevant integrator charm
Use a hosted Kubernetes distribution Enable the service via the provider

Register the Kubernetes cluster with Juju

Registering the cluster with Juju is known as “adding a cloud” in Juju’s terminology. A cloud is a deployment target. The exact process to register the cluster depends on how your system is configured.

When running MicroK8s

The cluster is registered with Juju automatically, but we have to enable some addons.

microk8s enable storage dns

Then move on to Create a Juju controller.

When you’re already able to interact with your cluster via kubectl

The registration process is a single command:

juju add-k8s

When you have used Juju to deploy Charmed Kubernetes

We can use Juju to extract its configuration file to save it locally with these commands:

mkdir ~/.kube
juju scp kubernetes-master/0:/home/ubuntu/config ~/.kube/config
juju add-k8s

Otherwise

Copy the cluster’s configuration file from the master node to your local machine and save it as $HOME/.kube/config, then run

juju add-k8s

Create a Juju controller

The Juju controller is a central software agent that oversees applications managed with Juju. It is created via the juju bootstrap command.

juju bootstrap <cloud-name> <controller-name>

Register storage resources

When an application that you wish to deploy - a “workload” in Juju terms - makes uses of persistent storage, you may need to ensure that an appropriate storage pool has been added to your Kubernetes cluster.

Juju will initially have a storage pool called “kubernetes”.

Charmed Kubernetes users can use Juju to provide it with storage based on Ceph or NFS.

The create-storage-pool command can be used to add new storage pools. For example:

juju create-storage-pool my-new-pool kubernetes storage-class=microk8s-hostpath

See Persistent storage and Kubernetes for more detail.

Add a model

Before deploying applications with charms, Juju users create a “model”. The model is a workspace for inter-related applications. It is an abstraction over applications, machines hosting them and other components such as persistent storage.

To add a model, use the juju add-model command:

juju add-model <k8s-cloud-name>

Inside the cluster, adding a Juju model creates a Kubernetes namespace with the same name. The namespace hosts all of the pods and other resources, except global resources.

Deploy a Kubernetes charm

A Kubernetes-specific charm is deployed in standard fashion, with the deploy command. If the charm has storage requirements you will need to specify them, as you do with a normal charm.

Configuration

The below table lists configuration keys supported by Kubernetes charms that are set at deploy time. The corresponding Kubernetes meaning can be obtained from the Kubernetes documentation for Services and Ingress.

Key Type Default
kubernetes-service-type string ClusterIP
kubernetes-service-external-ips string []
kubernetes-service-target-port string <container port>
kubernetes-service-loadbalancer-ip string ""
kubernetes-service-loadbalancer-sourceranges string "[]"
kubernetes-service-externalname string ""
kubernetes-ingress-class string nginx
kubernetes-ingress-ssl-redirect boolean false
kubernetes-ingress-ssl-passthrough boolean false
kubernetes-ingress-allow-http boolean false

For example:

juju deploy mariadb-k8s \
  --config kubernetes-service-loadbalancer-ip=10.1.1.1 \
  --storage database=100M,kubernetes

There are two other keys that are not Kubernetes-specific:

Key Type Default
juju-external-hostname string ""
juju-application-path string "/"

Keys ‘juju-external-hostname’ and ‘juju-application-path’ control how the application is exposed externally using a Kubernetes Ingress Resource in conjunction with the configured ingress controller (default: nginx).

Tutorials and in-depth guides

The following practical guides are available:

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