Concept
A Chart is a Helm package. It contains all of the resource definitions necessary to run an application, tool, or service inside of a Kubernetes cluster. Think of it like the Kubernetes equivalent of a Homebrew formula, an Apt dpkg, or a Yum RPM file.
A Repository is the place where charts can be collected and shared. It’s like Perl’s CPAN archive or the Fedora Package Database, but for Kubernetes packages.
A Release is an instance of a chart running in a Kubernetes cluster. One chart can often be installed many times into the same cluster. And each time it is installed, a new release is created. Consider a MySQL chart. If you want two databases running in your cluster, you can install that chart twice. Each one will have its own release, which will in turn have its own release name.
Helm installs charts into Kubernetes, creating a new release for each installation. And to find new charts, you can search Helm chart repositories.
Usage
To install a new package, use the helm install command. At its simplest, it takes two arguments: A release name that you pick, and the name of the chart you want to install.
helm install happy-panda bitnami/wordpress
To use new releases of the repo Helm chart, we’ll need to update our chart repository cache:
helm repo update
Customizing the Chart Before Installing
To see what options are configurable on a chart, use helm show values
helm install -f values.yaml bitnami/wordpress --generate-name
’helm upgrade’ and ‘helm rollback’: Upgrading a Release, and Recovering on Failure
When a new version of a chart is released, or when you want to change the configuration of your release, you can use the helm upgrade command.
Now, if something does not go as planned during a release, it is easy to roll back to a previous release using helm rollback [RELEASE] [REVISION].
And we can use helm history [RELEASE] to see revision numbers for a certain release.