Helm is a powerful tool for managing Kubernetes resources, simplifying the deployment and configuration of complex applications. When deploying or updating a Helm chart, commands like helm install and helm upgrade --install allow you to install or upgrade releases effortlessly. The --set command adds a layer of flexibility, enabling you to override default values in the values.yaml file directly through the command line.
This article breaks down how to use the --set flag effectively, its limitations, and when it’s better to opt for a values.yaml file. Whether you’re a Helm beginner or looking to sharpen your skills, you’ll find actionable insights and tips here.
What Is the --set Command?
The --set flag in Helm is a handy way to pass custom configuration values at runtime without editing the Helm chart’s values.yaml file. This can be especially useful for quick, one-off changes or environment-specific customizations.
Syntax Overview
Here’s the basic syntax for using the --set flag:
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helm install <release_name> <chart_name> —set key1=value1,key2=value2 |
Similarly, you can use it with helm upgrade --install:
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helm upgrade —install <release_name> <chart_name> —set key1=value1,key2=value2 |
Example Usage
Let’s say you’re deploying a Helm chart for an application. Here’s a real-world example:
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helm upgrade —install my–release my–chart —set replicaCount=3,image.tag=1.2.3 |
replicaCountis overridden to3.image.tagis set to1.2.3.
This approach works well for straightforward, small-scale overrides. But how do you figure out which keys to override? Let’s dive in.
How to Identify Keys for the --set Command
The --set flag relies on knowing the structure of the values.yaml file in the Helm chart. This file acts as a blueprint for the chart’s default configuration.
1. Examine the values.yaml File
The values.yaml file is typically located in the root directory of the Helm chart. It defines the default configuration, including values like replica counts, resource limits, and container images.
For example, a simple values.yaml file might look like this:
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replicaCount: 1 image: repository: nginx tag: latest |
If you want to override replicaCount, you can use:
To change the tag under image, use:
2. Use helm show values
If you don’t have direct access to the Helm chart, you can view its default configuration using the helm show values command:
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helm show values <chart_name> |
This command outputs the structure and default values of the chart’s values.yaml file, giving you a reference for creating overrides.
3. Understand Nested Keys
Nested keys in the values.yaml file are represented using dot notation. For instance:
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image: repository: my–app tag: stable |
To override tag, you’d use:
This dot notation is crucial for targeting specific values.
Challenges and Limitations of the --set Command
While the --set command is convenient, it has some limitations and quirks. Understanding these will help you avoid common pitfalls.
Escaping Special Characters
If your values contain special characters like commas or periods, you need to escape them. For example:
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—set key1=“value,with,commas”,key2=“value.with.periods” |
Alternatively, use the --set-string flag to treat the value as a literal string:
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—set–string version=“1.2.3” |
Overriding Arrays
Arrays in the values.yaml file require careful handling. For instance:
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env: – name: ENV_VAR_1 value: value1 – name: ENV_VAR_2 value: value2 |
To override the first array element:
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—set env[0].name=ENV_VAR_1,env[0].value=new_value |
Unfortunately, you cannot partially override arrays; you must supply the entire array.
Complex Nested Structures
Deeply nested configurations can become cumbersome to manage with --set. For example:
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—set ingress.annotations.“nginx\.ingress\.kubernetes\.io/rewrite-target”=/ |
For such cases, creating a custom values.yaml file is often simpler and more maintainable.
Best Practices for Using --set
To maximize the efficiency of the --set command, consider these best practices:
Use --set for Simple Overrides
Stick to small, straightforward changes like:
- Updating an image tag.
- Changing a replica count.
- Enabling or disabling a feature.
Opt for a Custom values.yaml File for Complex Configurations
For larger or more intricate changes, create a custom values.yaml file. Reference it with the -f flag:
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helm upgrade —install my–release my–chart –f custom–values.yaml |
This approach keeps your commands clean and configurations organized.
Combine Approaches
You can mix both methods. Use --set for temporary tweaks and a values.yaml file for stable configurations:
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helm upgrade —install my–release my–chart –f values.yaml —set image.tag=dev |
Version Control Your Configurations
Track your values.yaml files in version control. This enables better collaboration and ensures reproducibility across environments.
Should You Use --set or a values.yaml File?
The choice between --set and a values.yaml file depends on your use case. Here’s a quick comparison:
| Criteria | --set |
values.yaml |
|---|---|---|
| Best For | Quick, small changes | Large, reusable configurations |
| Readability | Hard to read with many overrides | Clear and structured |
| Version Control | Not version-controlled | Easy to version and share |
| Nested/Complex Values | Difficult to manage | Simplifies handling complex structures |
Recommendation: Use --set for temporary, environment-specific changes. For anything reusable or complex, stick with a values.yaml file. This ensures better clarity, maintainability, and collaboration.
Conclusion
The --set command is a versatile tool in the Helm ecosystem, perfect for quick overrides and environment-specific tweaks. However, its limitations make it unsuitable for complex configurations. By understanding when and how to use --set alongside values.yaml files, you can streamline your workflows, reduce errors, and maintain a clean deployment process. Embrace the best of both worlds to unlock the full potential of Helm!
