What Is the Difference Between Helm and Kustomize?

1. Overview

In Kubernetes, managing and deploying applications can be a complex task. To simplify this process, two popular tools have emerged:

• Helm
• Kustomize

These tools are designed to help developers and operations teams manage Kubernetes manifests and deployment. Although functionally related, they take different approaches to achieve this goal.

In this tutorial, we’ll discuss the features, benefits, and use cases of Helm and Kustomize, comparing their approaches to configuration management and providing tips for using each tool. Also, we’ll explore cases where integrating both tools can be beneficial.

2. Overview of Helm

Helm is a powerful package manager for Kubernetes that simplifies the process of deploying and managing applications. Further, it provides a way to package, configure, and deploy applications and services onto Kubernetes clusters using a packaging format called charts. In addition, Helm’s primary purpose is to make the deployment process easy, promote code reuse, and facilitate the management of complex deployments.

2.1. Features and Benefits

One of the essential features of Helm is its package management capabilities. Essentially, Helm uses a packaging format called charts. In short, charts are a collection of YAML files and templates that define the application’s components, dependencies, and configurations.

In addition to package management, Helm also introduces the concept of releases which represent a specific instance of a chart deployed to a Kubernetes cluster. With Helm, users can manage the lifecycle of releases including installation, upgrades, and rollbacks, using simple commands. This feature enables teams to have better control over their deployments and ensures a smooth application lifecycle management process.

Another significant benefit of Helm is its template rendering capability. Helm leverages Go templates to enable the dynamic generation of Kubernetes manifest based on user-provided values. This further enables parameterization and customization of deployments making it easier to adapt applications to different environments or configurations.

Moreover, Helm provides robust rollback and versioning features. It maintains a release history, enabling users to track and manage different versions of a deployed application. In case of issues or failures, Helm can roll back to a previous version of the release. This, therefore, minimizes downtime and ensures stability.

2.2. Helm’s Architecture

To understand Helm’s architecture, let’s explore its key components:

• Helm client: command-line tool that interacts with the Kubernetes API server and the Helm server (Tiller) to manage releases and deployments
• Helm server (Tiller): in Helm 3, Tiller has been removed and the Helm client directly interacts with the Kubernetes API server
• charts: packaging format used by Helm to define and encapsulate application configurations and dependencies
• repositories: remote servers that host and distribute charts

Public chart repositories, such as the official Helm Charts repository, provide a wide range of pre-packaged applications ready for deployment making it easier for teams to get started with Helm and use existing solutions.

3. Overview of Kustomize

Kustomize is a declarative configuration management tool for Kubernetes that enables users to customize and compose Kubernetes manifests without modifying the underlying YAML files directly. Its primary purpose is to provide a simple and flexible way to manage and customize Kubernetes resources across different environments or use cases.

3.1. Features and Benefits

Kustomize’s feature set focuses on customization and simplicity:

• declarative configuration management: users define the desired state of their Kubernetes resources using a declarative syntax, promoting readability, maintainability, and version control of Kubernetes configurations
• overlay and base customization: the base directory contains the common configuration files that serve as the foundation for different variations of the application, while overlay directories contain environment-specific or use case-specific customizations that are applied on top of the base configuration
• reusability and modularity: users can split their configurations into smaller, reusable components, define common resources such as ConfigMaps or Secrets in separate files, and reference them in multiple places
• patch and strategic merge patch: patches are small YAML files that describe the changes to be applied to the base configuration

In general, the benefit of a modular approach is that it reduces duplication and makes it easier to manage and update configurations across different parts of the application. Specifically, Kustomize even supports different types of patches, including JSON patches and strategic merge patches, which intelligently merge the change with the base configuration. Further, patches enable targeted modifications without the need to modify the original YAML files directly.

Therefore, Kustomize’s powerful features have made it a popular choice among Kubernetes users for managing and customizing their deployments effectively.

3.2. Kustomize Workflow

Kustomize introduces a straightforward workflow with key components:

• Kustomization files: specify the resources to include and the customizations to apply
• base directory: contains the original configuration
• overlay directory: contains modifications for specific use cases
• patches: apply changes to resources
• generators: create new resources based on predefined templates

The workflow promotes code reuse, modularity, and the ability to more easily manage multiple environments or variations of an application.

4. Comparison of Helm and Kustomize

When it comes to managing Kubernetes configurations, Helm and Kustomize offer different approaches and capabilities. Let’s compare these tools based on various aspects to understand their similarities and differences.

4.1. Approach to Configuration Management

Helm relies on a templating engine (Go templates) to generate Kubernetes manifests. It also uses a combination of YAML files and templates to define the application’s components and configurations. Moreover, Helm templates enable dynamic generation of manifests based on user-provided values.

In contrast, Kustomize follows a declarative approach to configuration management. It uses a base configuration and applies overlay or patches to customize the manifests for different environments or use cases. Therefore, Kustomize doesn’t rely on templating but instead uses a declarative syntax to define the desired state of Kubernetes resources.

4.2. Complexity and Learning Curve

Helm has a steeper learning curve compared to Kustomize due to its templating language and concepts like charts and releases. Users need to understand the Go templating syntax and the structure of Helm charts to effectively use all Helm features.

In contrast, Kustomize has a more straightforward approach to configuration management. Further, it uses a declarative syntax and relies on familiar Kubernetes concepts making it easier to understand and adopt. Kustomize’s learning curve is generally considered to be gentler compared to Helm.

4.3. Flexibility and Customization

Helm’s templating engine provides extensive customization options and dynamic generation of manifests. It supports the use of variables, conditionals, and loops to create flexible and reusable templates. Helm also provides hooks, which are scripts that can be executed at specific points during the release lifecycle, enabling advanced customization and automation.

Conversely, Kustomize focuses on declarative customization through overlays and patches. It enables users to modify and compose Kubernetes manifests by specifying the desired changes in a declarative manner. While Kustomize provides flexibility through its overlay and patch mechanisms, it may not be as extensive as Helm’s templating capabilities.

4.4. Package Management and Distribution

Helm excels in package management and distribution through its use of charts and repositories. Helm charts also provide a standardized format for packaging and distributing applications and their dependencies. Additionally, Helm repositories serve as a centralized location for storing and sharing charts making it easy to discover and deploy applications.

Kustomize doesn’t have built-in package management capabilities like Helm. However, it focuses on configuration management and relies on external tools or processes for packaging and distribution.

4.5. Community and Ecosystem

Helm has a large and mature community with a wide range of contributors and users. Additionally, the official Helm Charts repository provides an extensive collection of pre-packaged applications ready for deployment.

Kustomize also has a growing community and is gaining popularity among Kubernetes users. It’s integrated with the kubectl command-line tool making it easily accessible to Kubernetes users. While Kustomize’s community is smaller compared to Helm’s, it’s actively developing and expanding.

5. Use Cases and Scenarios

Now, let’s explore when to use each tool based on specific project requirements.

5.1. When to Use Helm

Helm is particularly useful when dealing with complex deployments that involve multiple components, dependencies, and configurations. It enables us to package all the necessary resources into a single chart making it easier to manage and deploy the entire application stack. Helm simplifies the management of complex deployments by generating manifests dynamically based on configurable values.

Furthermore, if a project requires robust package management and versioning capabilities, Helm is a strong choice. This is because Helm charts provide a standardized format for packaging applications and their dependencies making it easy to version, distribute, and manage them.

Moreover, when an application requires advanced templating features or the ability to execute custom scripts during the deployment lifecycle, Helm’s templating engine and hooks come in handy. In particular, the Go templating syntax has powerful customization and dynamic generation of manifests based on user-provided values. Hooks also enable us to perform additional actions such as running database migrations or post-deployment tasks as part of the deployment process.

5.2. When to Use Kustomize

Generally, Kustomize is a good fit for simpler deployments that have fewer variations across different environments or use cases. If an application doesn’t require extensive templating or complex customizations, Kustomize’s declarative approach can provide a straightforward and readable way to manage configurations. The overlay and patch mechanisms of Kustomize facilitate targeted modifications to the base configuration without introducing unnecessary complexity.

Additionally, Kustomize can define the desired state of Kubernetes resources using a declarative syntax. Thus, if a project prioritizes a declarative approach to configuration management, Kustomize can be the best fit for that purpose.

6. Integrating Helm and Kustomize

No doubt, these two tools are powerful on their own. However, combining both can be even more powerful for a more flexible deployment workflow. Let’s explore how Helm and Kustomize can be integrated and the approaches to achieve this integration.

6.1. Using Kustomize to Customize Helm Charts

We can use Kustomize to modify and customize Helm chats by applying patches or overlays to the rendered manifests. This way, we use Helm for packaging and templating while leveraging Kustomize for environment-specific customizations.

Let’s see an example of kustomization.yaml file that references a Helm chart:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
- helm-chart.yaml
patchesStrategicMerge:
- patch.yaml

In this example, helm-chart.yaml is a rendered Helm chart, and patch.yaml contains the Kustomize patches to modify the chart.

6.2. Helm as a Package Manager With Kustomize

We can also use Helm as a package manager to manage and deploy Helm charts while using Kustomize for further customization. Thus, we benefit from Helm’s packaging and release management features while still having the flexibility to customize the deployed resources using Kustomize.

Let’s look at an example of a kustomization.yaml file that includes a Helm chart as a resource:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
helmCharts:
- name: myapp
  repo: https://charts.example.com
  version: 1.2.3
  valuesFile: myapp-values.yaml
patchesStrategicMerge:
- patch.yaml

In this example, the Helm chart myapp is included as a resource in the kustomization.yaml file specifying the chart repository, version, and values file. Additionally, patch.yaml contains the Kustomize patches to customize the deployed resources.

7. Conclusion

In this article, we explored the differences and similarities between Helm and Kustomize, two popular tools for managing Kubernetes configurations. We also delved into their key features, benefits, and use cases, highlighting their strengths and weaknesses.

To recap, Helm is a powerful package manager that excels in managing complex deployments, providing templating capabilities, and offering robust release management. It has a steeper learning curve but offers extensive flexibility and a large ecosystem of pre-packaged charts.

On the other hand, Kustomize follows a declarative approach to configuration management, focusing on simplicity and modularity. It shines in scenarios where we need to customize and compose Kubernetes manifests without the need for complex templating. Kustomize has a gentler learning curve and integrates well with existing Kubernetes workflows.

In some cases, integrating both tools can provide the best experience, enabling us to leverage Helm’s packaging and templating capabilities while using Kustomize for further customization.