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Use Helm and Kustomize to install cluster components

Helm

Helm is synonymous to what apt or yum are in the Linux world. It's effectively a package manager for Kubernetes. "Packages" in Helm are called charts to which you can customise with your own values.

It's unlikely the exam will require anyone to create a helm chart from scratch, but an understanding of how it works is a good idea.

Helm Repos

Repos are where helm charts are stored. Typically, a repo will contain a number of charts to choose from. Helm can be managed by a CLI client, and a repo can be added by running:

helm repo add bitnami https://charts.bitnami.com/bitnami

To list the packages from this repo:

helm search repo bitnami

To install a package from this repo:

helm install my-release bitnami/mariadb

Where my-release is a string identifying an installed instance of this application

Parameters that can be customised - are dependent on how the chart is configured. For the aforementioned MariaDB chart, they are listed at https://github.com/bitnami/charts/tree/master/bitnami/mariadb/#parameters

These values are encapsulated in the corresponding values.yaml file in the repo. You can populate an instance of it and apply it with:

helm install -f https://raw.githubusercontent.com/bitnami/charts/master/bitnami/mariadb/values.yaml my-release bitnami/mariadb

Alternatively, variables can be declared by using --set, such as:

helm install my-release --set auth.rootPassword=secretpassword bitnami/mariadb

Kustomize

Kustomize is a templating tool for Kubernetes manifests in its native form (Yaml). When working with raw YAML files you will typically have a directory containing several files identifying the resources it creates. To begin, a directory containing our manifests needs to exist:

/home/david/app/base
total 16
drwxrwxr-x  2 david david 4096 Feb  9 11:44 .
drwxr-xr-x 27 david david 4096 Feb  9 11:44 ..
-rw-rw-r--  1 david david  340 Feb  9 11:09 deployment.yaml
-rw-rw-r--  1 david david  153 Feb  9 11:09 service.yaml

This will form our base - we will build on this but adding customisations in the form of overlays. First, we need a kustomize file. which can be created with kustomize create --autodetect

This will create kustomization.yaml in the current directory:

total 20
drwxrwxr-x  2 david david 4096 Feb  9 11:47 .
drwxr-xr-x 27 david david 4096 Feb  9 11:47 ..
-rw-rw-r--  1 david david  340 Feb  9 11:09 deployment.yaml
-rw-rw-r--  1 david david  108 Feb  9 11:47 kustomization.yaml
-rw-rw-r--  1 david david  153 Feb  9 11:09 service.yaml

The contents being:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
- deployment.yaml
- service.yaml

Variants and Overlays

  • variant - Divergence in configuration from the base
  • overlay - Composes variants together

Say, for example, we wanted to generate manifests for different environments (prod and dev) that are based from this config, but have additional customisations. In this example we will create a dev variant encapsulated in a single Overlay

mkdir -p overlays/{dev,prod}
cd overlays/dev

Begin by creating a Kustomization object specifying the base (this will create kustomization.yaml) :

kustomize create --resources ../../base

In this example, I want to change the replica count to 1, as it's a dev environment. In the dev directory, create a new file deployment.yaml containing:

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: nginx
  name: nginx-deployment
spec:
  replicas: 1

The kustomization.yaml file needs modifying to include a patchesStrategicMerge block:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
bases:
  - ../../base
patchesStrategicMerge:
  - deployment.yaml

Patches can be used to apply different customizations to Resources. Kustomize supports different patching mechanisms through patchesStrategicMerge and patchesJson6902. patchesStrategicMerge is a list of file paths.

We can generate the manifests and apply to the cluster by executing (from the base folder):

kustomize build ./overlay/dev | kubectl apply -f -

By running this, only 1 pod will be created in the deployment object, instead of what's defined in the base because of the customisation we've applied. We can do the same with prod, or any arbitrary number of environments.

Exam Tip

Practice with upstream Helm charts for applications that interest you. Dig into how values.yaml work