🐶
Kubernetes

Kubernetes Helm: Combine Variables with String in Templates

By Jan on 02/10/2025

Learn how to seamlessly combine two Kubernetes Helm variables with a string in the middle for more dynamic and efficient deployments.

Kubernetes Helm: Combine Variables with String in Templates

Table of Contents

Introduction

Helm templates provide a powerful way to dynamically generate Kubernetes manifests. String concatenation is a common requirement when crafting these templates, allowing you to build values from variables and inputs. This guide covers various techniques for string concatenation in Helm templates, empowering you to create flexible and reusable deployments.

Step-by-Step Guide

  1. Basic String Concatenation: You can concatenate strings in Helm templates using the printf function.

    name: {{ printf "%s-%s" .Values.firstVariable .Values.secondVariable }}

  2. Adding a String in Between: To insert a string between variables, include it within the format string of the printf function.

    name: {{ printf "%s-my-string-%s" .Values.firstVariable .Values.secondVariable }}

  3. Using with Ranges: When using ranges, you can access the current item's values using . and the variable name.

    {{- range .Values.items }}
name: {{ printf "%s-%s" .name .value }}
{{- end }}

  4. Ternary Operator and Concatenation: You can combine ternary operators with string concatenation for conditional logic.

    name: {{ printf "%s%s" .Values.firstVariable (ternary "-suffix" "" .Values.condition) }}

  5. Quoting Values: For values that might need quoting (like multi-line strings), use the quote function.

    value: {{ quote .Values.multilineString }}

Remember that Helm uses Go template syntax, so refer to the Go template documentation for more advanced string manipulation techniques.

Code Example

This code demonstrates string concatenation techniques in a Helm chart. It covers concatenating variables with separators, adding custom strings, iterating through lists and concatenating values, conditional concatenation based on a boolean value, and using the quote function to preserve formatting of multiline strings. These techniques are applied to dynamically generate deployment names, labels, and environment variables.

This example demonstrates various string concatenation techniques in a Helm chart.

values.yaml:

firstVariable: "hello"
secondVariable: "world"
items:
  - name: "item1"
    value: "one"
  - name: "item2"
    value: "two"
condition: true
multilineString: |
  This is a
  multi-line
  string.

templates/deployment.yaml:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: {{ printf "%s-%s" .Values.firstVariable .Values.secondVariable }}
spec:
  replicas: 1
  template:
    metadata:
      labels:
        app: {{ printf "%s-my-string-%s" .Values.firstVariable .Values.secondVariable }}
    spec:
      containers:
      - name: my-container
        image: nginx:latest
        env:
        {{- range .Values.items }}
        - name: {{ printf "%s-ENV" .name }}
          value: {{ printf "%s-%s" .name .value }}
        {{- end }}
        - name: CONDITIONAL_SUFFIX
          value: {{ printf "%s%s" .Values.firstVariable (ternary "-suffix" "" .Values.condition) }}
        - name: MULTILINE_VALUE
          value: {{ quote .Values.multilineString }}

Explanation:

  1. Deployment Name: The deployment name is created by concatenating firstVariable and secondVariable with a hyphen in between.
  2. App Label: The app label demonstrates adding a custom string ("-my-string-") between the concatenated variables.
  3. Environment Variables from Range: This section iterates through the items list and creates environment variables by concatenating the item's name and value.
  4. Conditional Suffix: This example shows how to conditionally add a suffix ("-suffix") to firstVariable based on the boolean value of condition.
  5. Multiline String: The multilineString is quoted using the quote function to preserve its formatting when used as an environment variable value.

This example demonstrates various ways to concatenate strings in Helm charts, allowing you to dynamically generate resource names, labels, annotations, and other configuration values based on your application's needs.

Additional Notes

  • Alternatives to printf: While printf offers flexibility, for simple concatenations, using the - operator within curly braces can be more concise: 
    name: {{ .Values.firstVariable - .Values.secondVariable }}
  • Whitespace Management: Be mindful of whitespace within the printf format string and surrounding curly braces. Unwanted spaces might lead to unexpected results. Use - to control spacing.
  • Error Handling: If a variable used in concatenation might be undefined, consider using default values (default) or other error handling mechanisms to prevent template rendering failures.
  • String Functions: Explore other Go template string functions like upper, lower, trim, and regexReplace for more advanced string manipulations within your Helm charts.
  • Readability: For complex concatenations, break them down into multiple lines or use intermediate variables for improved readability and maintainability.
  • Security Considerations: Avoid concatenating sensitive information directly within templates. Use secrets and other secure mechanisms for handling sensitive data.

Summary

This table summarizes various string concatenation techniques in Helm templates:

Method Description Example
Basic Concatenation Use printf to combine strings and variables. name: {{ printf "%s-%s" .Values.firstVariable .Values.secondVariable }}
Adding a String Include the desired string within the printf format string. name: {{ printf "%s-my-string-%s" .Values.firstVariable .Values.secondVariable }}
Concatenation in Ranges Access range item values using . within the loop. {{- range .Values.items }} name: {{ printf "%s-%s" .name .value }} {{- end }}
Ternary Operator Combine ternary operators with printf for conditional concatenation. name: {{ printf "%s%s" .Values.firstVariable (ternary "-suffix" "" .Values.condition) }}
Quoting Values Use quote to handle values requiring quotes, like multi-line strings. value: {{ quote .Values.multilineString }}

Note: Helm uses Go template syntax. Refer to the Go template documentation for advanced string manipulation.

Conclusion

Mastering string concatenation in Helm templates empowers you to create adaptable and efficient Kubernetes deployments. By leveraging the techniques outlined in this guide, you can dynamically generate values, craft reusable templates, and streamline your infrastructure management. Remember to consult the Helm and Go template documentation for advanced use cases and explore additional string manipulation functions to enhance your Helm chart development process.

References

Were You Able to Follow the Instructions?

😍Love it!
😊Yes
😐Meh-gical
😞No
🤮Clickbait

Related posts

Understanding Minikube docker-env Command

Learn how the minikube docker-env command integrates your local Docker environment with your minikube cluster for seamless development and testing.

Kubernetes Nodes Not Ready: Troubleshooting Guide

Learn the common causes and troubleshooting steps for Kubernetes nodes stuck in 'Not Ready' state, covering network issues, resource constraints, kubelet problems, and more.

Find kubeadm join command on master node

Learn how to easily locate the kubeadm join command on your Kubernetes master node for adding worker nodes to your cluster.