Packaging Applications

In this chapter, we are going to look at Helm, the Kubernetes package manager. Every successful and non-trivial platform must have a good packaging system. Helm was developed by Deis (acquired by Microsoft in April 2017) and later contributed to the Kubernetes project directly. It became a CNCF project in 2018. We will start by understanding the motivation for Helm, its architecture, and its components. Then, we'll get hands-on and demonstrate how to use Helm and its charts within Kubernetes. That includes finding, installing, customizing, deleting, and managing charts. Last but not least, we'll cover how to create your own charts and handle versioning, dependencies, and templating.

The topics we will cover are as follows:

• Understanding Helm
• Using Helm
• Creating your own charts

Understanding Helm

Kubernetes provides many ways to organize and orchestrate your containers at runtime, but it lacks a higher-level organization for grouping sets of images together. This is where Helm comes in. In this section, we'll go over the motivation for Helm, its architecture and components, and discuss what has changed in the transition from Helm 2 to Helm 3.

The motivation for Helm

Helm provides support for several important use cases:

• Managing complexity
• Easy upgrades
• Simple sharing
• Safe rollbacks

Charts can describe even the most complex apps, provide repeatable application installation, and serve as a single point of authority. In-place upgrades and custom hooks allow easy updates. It's simple to share charts that can be versioned and hosted on public or private servers. When you need to roll back recent upgrades, Helm provides a single command that allows you to roll back a cohesive set of changes to your infrastructure...

Using Helm

Helm is a rich package management system that lets you perform all the necessary steps to manage the applications installed on your cluster. Let's roll up our sleeves and get going. We'll look at installing both Helm 2 and Helm 3, but we will use Helm 3 for all of our hands-on experiments and demonstrations.

Installing Helm

Installing Helm involves installing the client and the server. Helm is implemented in Go. The Helm 2 executable can serve as either the client or the server. Helm 3, as mentioned before, is a client-only program.

Installing the Helm client

You must have Kubectl configured properly to talk to your Kubernetes cluster because the Helm client uses the Kubectl configuration to talk to the Helm server (Tiller).

Helm provides binary releases for all platforms here:

https://github.com/helm/helm/releases

For Windows, the chocolatey package manager is the best option (and is usually up to date):

choco install kubernetes...

Creating your own charts

A chart is a collection of files that describe a related set of Kubernetes resources. A single chart might be used to deploy something simple, such as a Memcached pod, or something complex, such as a full web app stack with HTTP servers, databases, caches, queues, and so on.

Charts are created as files laid out in a particular directory tree. Then, they can be packaged into versioned archives to be deployed. The key file is Chart.yaml.

The Chart.yaml file

The Chart.yaml file is the main file of a Helm chart. It requires name and version fields:

• name: The name of the chart (same as the directory name)
• version: A SemVer 2 version

It may also contain various optional fields:

• kubeVersion: A SemVer range of compatible Kubernetes versions
• description: A single sentence describing this project
• keywords: A list of keywords about this project
• home: The URL of this project's home page
• sources...

Summary

In this chapter, we took a look at Helm, the Kubernetes package manager. Helm gives Kubernetes the ability to manage complicated software composed of many Kubernetes resources with inter-dependencies. It serves the same purpose as an OS package manager. It organizes packages and lets you search charts, install and upgrade charts, and share charts with collaborators. You can develop your own charts and store them in repositories. Helm 3 is a client-side-only solution that uses CRDs to manage the status of releases, instead of the Tiller server-side component of Helm 2, which poses a lot of security issues with its default configuration.

At this point, you should be able to understand the important role that Helm serves in the Kubernetes ecosystem and community. You should be able to use it productively and even develop and share your own charts.

In the next chapter, we will look at how Kubernetes does networking at a pretty low level.