Helm Basics on OpenShift

Helm is the package manager for Kubernetes, and it’s extensively used to simplify the deployment and management of applications on Kubernetes clusters, including OpenShift. For a developer working on OpenShift, understanding Helm basics is crucial for deploying and managing their applications efficiently.

Here’s a summary of the basics for developers using Helm on OpenShift:

What is Helm? Helm helps you manage Kubernetes applications. Helm Charts are packages of pre-configured Kubernetes resources. Think of it like a package manager for your operating system (e.g., apt, yum, brew) but for Kubernetes applications. It simplifies defining, installing, and upgrading even complex applications.

Why use Helm on OpenShift?

• Application Packaging: Standardizes how your application (and its dependencies) are packaged for deployment.
• Version Control: Allows versioning of your application deployments.
• Easy Deployment/Upgrade/Rollback: Simplifies the lifecycle management of applications.
• Configuration Management: Manages configurations for different environments (dev, test, prod) using values.yaml files.
• Reusable Templates: Provides templates for common Kubernetes objects, reducing boilerplate YAML.

Essential Helm Commands

• helm create <chart-name>:
  • Purpose: Initializes a new Helm chart directory with a basic structure (templates, Chart.yaml, values.yaml). This is your starting point for packaging an application.
  • When to use: When you’re creating a new application and want to define its deployment using Helm, or when you need a template to understand the chart structure.
• helm lint <path-to-chart>:
  • Purpose: Verifies that your chart follows best practices and is syntactically correct. It checks for common issues and potential errors.
  • When to use: Regularly during chart development to catch errors early.
• helm install <release-name> <path-to-chart> -n <namespace>:
  • Purpose: Deploys a new instance of your application (a “release”) onto the OpenShift cluster in a specified namespace. You provide a unique release name for this deployment.
  • When to use: To perform the initial deployment of your application.
  • OpenShift Consideration: Ensure your user has create permissions in the target namespace. Helm will create Kubernetes resources, and OpenShift’s Security Context Constraints (SCCs) might require adjustments to your pod definitions (e.g., specifying a serviceAccountName) if your application needs elevated privileges or specific UIDs.
• helm upgrade <release-name> <path-to-chart> -n <namespace>:
  • Purpose: Updates an existing release of your application to a new version of the chart or new configuration values. Helm intelligently calculates the differences and applies necessary changes.
  • When to use: When you’ve made changes to your application’s code, Docker image, or Helm chart configurations and want to deploy the updated version without reinstalling.
  • OpenShift Consideration: Often used with the --install flag (helm upgrade --install ...) which will install the release if it doesn’t exist, or upgrade it if it does.
• helm uninstall <release-name> -n <namespace>:
  • Purpose: Removes a deployed release from the OpenShift cluster, deleting all associated Kubernetes resources.
  • When to use: When you’re done with a particular deployment, cleaning up resources, or before re-deploying from scratch.
• helm list -n <namespace> or helm ls -n <namespace>:
  • Purpose: Lists all releases currently deployed in a given namespace on the cluster. It shows the release name, chart version, status, and namespace.
  • When to use: To see what applications are deployed, their status, and their release names for further management.
• helm status <release-name> -n <namespace>:
  • Purpose: Shows the status of a specific release, including the deployed resources, hooks, and notes from the chart.
  • When to use: To quickly check if a deployment was successful and to get details about its current state and the resources it manages.
• helm get values <release-name> -n <namespace>:
  • Purpose: Retrieves the values that were used to install or upgrade a specific release. This is very useful for debugging or understanding the configuration of a running application.
  • When to use: When you need to inspect the live configuration values of a deployed application.
• helm template <path-to-chart> --values <your-values.yaml> -n <namespace>:
  • Purpose: Renders the Kubernetes YAML manifests that would be generated by a chart, without actually deploying them to the cluster. This is invaluable for debugging and understanding what Helm will do.
  • When to use: Before deploying, to inspect the generated YAML and ensure it matches your expectations, especially when working with complex values.yaml files.
• Working with values.yaml:
  • Purpose: This file within a Helm chart defines the configurable parameters for your application. Developers can override these default values during install or upgrade using the -f flag (--values <my-custom-values.yaml>).
  • When to use: To customize application configurations (e.g., image tags, replica counts, environment variables, resource limits) for different environments or specific deployments.

By mastering these basic Helm commands and concepts, developers can efficiently package, deploy, and manage their containerized applications on OpenShift.