Skip to content

2020-07-07 Kubernetes

Helm Overview

Helm Overview#

Deploying applications on k8s can be complex. Setting up a single application involves creating multiple interdependent k8s resources: deployments, pods, services and replicasets. Each requires you to write detailed yaml.

Helm is a package manager for k8s. Making it easier to package, configure and deploy applications on k8s.

Most every programming language and operating system has its own package manager to help with the installation and maintenance of software - Helm has similar features.

Helm can:

  • Install software
  • install dependencies
  • Upgrade software
  • Configure software deployments
  • Fetch software packages from repos

It has the following components:

  • CLI tool
  • Tiller (not a thing since 3.0.0) a server component listening for changes from helm
  • Charts - the helm packaging format
  • An official chart repository

Charts#

Helm packages are called charts.

The basic structure of a chart:

package-name/
    charts/
    templates/
    Chart.yaml
    LICENSE
    README.md
    requirements.yaml
    values.yaml
  • charts/ - Manually managed chart dependencies (it is better to use requirements.txt)
  • templates/ - template files that are combined with values.yaml and rendered into k8s manifests - templates use the go programming language template format.
  • Chart.yaml - Metadata about the chart - version, maintainer info
  • LICENSE - plaintext licence
  • requirements.yaml - dependencies
  • values.yaml - configuration for the templates for the chart

helm can install from a local directory or a .tar.gz

Chart Repositories#

A Helm chart repo is a simple HTTP site that serves an index.yaml file and .tar.gz packaged charts

The default stable chart repo is https://kubernetes-charts.storage.googleapis.com

More repos can be added with helm repo add

Chart Configuration#

A chart usually comes with a default config in values.yaml - some applications can be fully deployable with default values.

Eg.

service:
  type: ClusterIP
  port: 3306

To dump the config for a chart:

helm inspect values chart-name

The values can be overridden with your own and then installed with:

helm install

A Helm chart deployed with a particular configuration is called a release

Releases#

Helm combines the defaults with the user provided vars. These are rendered into k8s manifests and deployed vie the k8s api.

Important cause you may want to deploy the same application more than once.

Creating Charts#

Use:

helm create chart-name

Fill out Chart.yaml and then put your manifests into the templates directory. Extract the relevant info out of the manifest and into your values.yaml file - then include them with the templating system.

Using Helm#

Install the kubernetes dashboard from the stable repo

helm install stable/kubernetes-dashboard --name dashboard-demo

Oops it complained:

Error: could not find tiller

Cause I was still on v2:

$ helm version
Client: &version.Version{SemVer:"v2.16.0", GitCommit:"e13bc94621d4ef666270cfbe734aaabf342a49bb", GitTreeState:"clean"}

So ensure to:

brew upgrade helm

List repos:

$ helm repo list
Error: no repositories to show

Add a repo:

helm repo add stable https://kubernetes-charts.storage.googleapis.com/

Search:

helm search repo stable

The new way to install a helm chart:

helm install dashboard-demo stable/kubernetes-dashboard

Get a list of releases on the cluster:

helm list

It will now be on the k8s cluster:

kubectl get services

Update the release by changing the name:

helm upgrade dashboard-demo stable/kubernetes-dashboard --set fullnameOverride="dashboard"

That changed it:

$ kubectl get services
NAME         TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)   AGE
dashboard    ClusterIP   10.101.89.209   <none>        443/TCP   16s
kubernetes   ClusterIP   10.96.0.1       <none>        443/TCP   10h

Apparently you can proxy to the dashboard (hardly works for me)

kubectl proxy
http://localhost:8001/api/v1/namespaces/default/services/dashboard/proxy/

List the releases:

$ helm list
NAME            NAMESPACE       REVISION        UPDATED                                 STATUS          CHART                           APP VERSION
dashboard-demo  default         2               2020-01-07 11:13:12.959096 +0200 SAST   deployed        kubernetes-dashboard-1.10.1     1.10.1

we are now going to rollback to the previous version

helm rollback dashboard-demo 1
Rollback was a success! Happy Helming!

The service name has rolled back

$ kubectl get services
NAME                                  TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)   AGE
dashboard-demo-kubernetes-dashboard   ClusterIP   10.98.80.137   <none>        443/TCP   2m
kubernetes                            ClusterIP   10.96.0.1      <none>        443/TCP   10h

Delete a release:

helm delete dashboard-demo
release "dashboard-demo" uninstalled

Helm still keeps the revision info, even for deleted releases. (I think this was only version 2)

So it is better to uninstall I think now:

helm uninstall dashboard-demo

and then list the uninstalled items with:

helm list --all

More Info#

For more info check the Helm Docs

Sources#