Deploy Packages with Helm

Helm is the OLCF preferred package manager for Kubernetes. There are a variety of upstream applications that can be installed with helm, such as databases, web frontends, and monitoring tools. Helm has “packages” called “charts”, which can essentially be thought of as kubernetes object templates. You can pass in values which helm uses to fill in these templates, and create the objects (pods, deployments, services, etc)

Follow Helm Prerequisites for installing Helm.

One nice feature of helm is that it uses the underlying authentication credentials to kubernetes, so once you login with oc login, the helm client will authenticate automatically.

By default, helm doesn’t have any chart repositories, so let’s add the upstream stable repository.

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

Now you can install helm charts with helm install stable/<package_name>. You can think of this command as a parallel to running yum install on a RHEL/CentOS-based system, or apt install on a debian-based system.

Install MySQL with Helm

For an example, let’s install a basic mysql database, with a release named mysql.

Setting Values

You could simply run helm install mysql stable/mysql, and an basic mysql deployment would be created with default values. However, we probably want to customize this deployment a bit. Let’s take a look at the documentation for the mysql helm chart.

Under the “Configuration” section, there is a large list of all the variables you can provide the chart, as well as their default values. Let’s say we want to customize our mysql resource utilization as well as using a block volume instead of the default NFS volume for persistent storage. We’ll also add a NodePort service in order to access our new database from outside the cluster.

There are two ways to set values for helm install:

  1. Pass in individual values one-by-one with --set.
  2. Pass in a group of values within a file with --values.

In this example, we’ll be using the latter method. Let’s create a file called values.yaml with the following values:

persistence:
  size: 20Gi
  storageClass: "netapp-block"
initContainer:
  resources:
    requests:
      cpu: 100m
      memory: 10Mi
    limits:
      cpu: 300m
      memory: 100Mi
resources:
  requests:
    cpu: 2
    memory: 2Gi
  limits:
    cpu: 4
    memory:4Gi
service:
  type: NodePort

Now mysql can be installed with these values by running helm install mysql stable/mysql --values values.yaml --namespace <project_name>

Note

To install quickly with --set instead of writing a values file, for example, if the default values are preferred except the persistent storage size and storageClass, this could be done by running helm install mysql stable/mysql --set persistence.size="20Gi" --set persistence.storageClass="netapp-block". Note that you can pass multiple values by passing --set multiple times.

After Installation

To see all deployed helm charts in a namespace, along with their status, run helm list --namespace <project_name> If following the above example, this command will show the new mysql deployment, with mysql under NAME.

You can run helm status <release_name> --namespace <project_name> in order to get information about the deployment. In this example, our release name is mysql. Running this command for our mysql installation will give us information on how to connect and authenticate to our newly created database.

The output of helm status will differ from chart to chart, as this output is customizable by the chart itself. If the output has kubectl commands to run, kubectl can be replaced with oc.

Finding New Charts

Running helm search hub will search the Helm Hub, which has a wide variety of publicly available charts. For example, if a wordpress installation is desired, you could run:

$ helm search hub wordpress
URL                                                 CHART VERSION   APP VERSION DESCRIPTION
https://hub.helm.sh/charts/bitnami/wordpress        7.6.7           5.2.4       Web publishing platform for building blogs and ...
https://hub.helm.sh/charts/presslabs/wordpress-...  v0.6.3          v0.6.3      Presslabs WordPress Operator Helm Chart
https://hub.helm.sh/charts/presslabs/wordpress-...  v0.7.1          v0.7.1

Note that this searches much more than the stable repo we added above, so you may need to add another repo with helm repo add. Be sure to run helm repo update before installing new charts, to make sure the charts are up to date.

You can also search only the repos that you have added to your local client with helm search repo

Writing Charts

It is also possible to write your own charts for helm, if you have an application that can be deployed to many namespaces or that could benefit from templating objects. How to write charts is outside the scope of this documentation, but the upstream docs are a great place to start.