Background and Review

POP QUIZ!

Try to answer each question before expanding the section to see how strong your current understanding of Helm is.

What is Helm and what problem does it solve?

Answer

Helm is a package manager for Kubernetes that simplifies the deployment and management of applications.
It solves several key problems:

  • Complexity: Kubernetes manifests can be complex and repetitive.
    Helm packages these manifests into reusable charts.

  • Configuration Management: Helm provides a templating system that allows you to customize deployments without modifying the original manifests.

  • Versioning: Helm tracks versions of your deployments, making it easier to roll back to previous configurations.

  • Dependency Management: Helm can manage dependencies between different Kubernetes resources.

What are the main components of a Helm chart?

Answer

A Helm chart consists of several key components including:

  • Chart.yaml: Contains metadata about the chart, including its name, version, and description.

  • values.yaml: Contains default configuration values that can be overridden during installation or upgrade.

  • templates/: A directory containing Kubernetes manifest templates written in Go template syntax.

  • charts/: An optional directory containing chart dependencies.

  • README.md: Documentation explaining how to use the chart.

What is the difference between a Helm chart and a Helm release?

Answer

A Helm chart is a collection of files that describe a set of Kubernetes resources.
It is a package that can be versioned, shared, and reused.
A chart is like a class in programming.

A Helm release is an instance of a chart that has been deployed to a Kubernetes cluster.
When you install a chart, Helm creates a release with a unique name.
You can have multiple releases of the same chart, each with different configurations.
A release tracks the state of the deployed resources and allows you to upgrade, rollback, or uninstall the resources.

What is the purpose of values.yaml in a Helm chart?

Answer

The values.yaml file serves as the default configuration file for a Helm chart.
It defines default values that are used when rendering the templates in the chart.

Key purposes include:

  • Default Configuration: Provides sensible defaults for all configurable parameters in the chart.

  • Documentation: Acts as documentation by showing all available configuration options and their default values.

  • Customization: Allows users to override these defaults when installing or upgrading a release, either by providing a custom values file or using the --set flag.

  • Separation of Concerns: Separates configuration from template logic, making charts more maintainable and easier to customize.

What is a Helm repository and how is it used?

Answer

A Helm repository is a location where Helm charts are stored and can be shared.
It is typically an HTTP server that serves an index.yaml file containing metadata about available charts.

Helm repositories are used to:

  • Share Charts: Distribute charts to teams or the public.

  • Version Management: Track multiple versions of charts in a centralized location.

  • Discovery: Make it easy to find and install charts using helm search commands.

To use a repository, you add it with helm repo add <name> <url>, update the local cache with helm repo update, and then install charts from it using helm install <release-name> <repo-name>/<chart-name>.

What is the difference between helm install and helm upgrade?

Answer

helm install is used to create a new release by installing a chart for the first time.
It deploys the chart’s resources to the Kubernetes cluster and creates a new release record.

helm upgrade is used to update an existing release to a new version of a chart or with new configuration values.
It modifies the existing resources in the cluster based on the differences between the current and desired state.

Key differences:

  • Install creates a new release; upgrade modifies an existing one.

  • Install requires a unique release name; upgrade uses the name of an existing release.

  • Upgrade can use the --install flag to create a release if it doesn’t exist, combining both operations.

What is a Helm template and how does templating work?

Answer

A Helm template is a Kubernetes manifest file that contains placeholders written in Go template syntax.
These placeholders are replaced with actual values when Helm renders the chart.

Templating allows you to:

  • Parameterize Resources: Use variables like {{ .Values.replicas }} to make resource counts configurable.

  • Conditional Logic: Use {{ if }} statements to include or exclude resources based on configuration.

  • Loops: Use {{ range }} to create multiple resources from a list.

  • Access Built-in Objects: Access information like release name, namespace, and chart metadata using objects like {{ .Release.Name }} and {{ .Chart.Name }}.

When you run helm install or helm upgrade, Helm processes all templates in the templates/ directory, replaces the placeholders with values from values.yaml and any overrides, and sends the rendered manifests to Kubernetes.

How are dependencies defined and managed in Chart.yaml?

Answer

Dependencies in Helm charts are defined in the dependencies section of the Chart.yaml file.
Each dependency specifies another chart that must be installed before the current chart can be deployed.

A dependency entry includes:

  • Name: The name of the dependent chart.

  • Version: The version or version range of the chart to use (e.g., "1.2.3" or "~1.2.0").

  • Repository: The URL of the Helm repository where the chart can be found, or "file://" for local chart dependencies.

  • Condition: An optional condition that determines whether the dependency should be installed (useful for optional dependencies).

  • Tags: Optional tags that can be used to group dependencies and control their installation.

To use dependencies, you run helm dependency update, which downloads the specified charts into the charts/ directory.
Helm then installs these dependencies before installing the main chart, ensuring that all required resources are available.
Dependencies are installed as sub-charts and can be accessed in templates using the .Chart.Dependencies object.

How does Helm manage rollbacks and what information does it track?

Answer

Helm tracks the history of each release, storing information about every install, upgrade, and rollback operation.
This history includes:

  • Release Version: Each operation increments the release revision number.

  • Chart Version: The version of the chart that was deployed.

  • Configuration: The values that were used for that revision.

  • Status: Whether the release was successful, pending, or failed.

  • Description: Optional notes about what changed in that revision.

To rollback, you use helm rollback <release-name> <revision-number>, which reinstalls the resources from the specified revision.
Helm maintains this history in Kubernetes secrets, allowing you to see all revisions with helm history <release-name> and revert to any previous state if needed.

If you could not answer all of the questions, that is perfectlyokay.
We will be reviewing these concepts and exploring more advanced topics as we progress through the workshop.