Conditionals

In this article, we explore how to use conditionals in Helm charts to include or exclude sections of your templates based on values specified in the values file. With these techniques, you can add optional configurations such as custom labels, control whitespace, and conditionally render entire objects like service accounts—all of which add flexibility to your deployments.

Example: Adding Optional Labels

Consider a basic Helm chart with a simple service template. Initially, you might have a values.yaml file with minimal configuration and a corresponding service.yaml template:

# values.yaml
replicaCount: 2
image: nginx

# service.yaml
apiVersion: v1
kind: Service
metadata:
  name: {{ .Release.Name }}-nginx
spec:
  ports:
    - port: 80
      name: http
  selector:
    app: hello-world

Now, suppose different releases require different labels—for example, adding an organizational label to group objects. You can update your configuration as follows:

# values.yaml
replicaCount: 2
image: nginx
orgLabel: payroll

# service.yaml
apiVersion: v1
kind: Service
metadata:
  name: {{ .Release.Name }}-nginx
  labels:
    org: payroll
spec:
  ports:
    - port: 80
      name: http
  selector:
    app: hello-world

However, when the orgLabel value is optional, you want these label lines to appear only when the value is provided. Similar to conditionally executing code in programming languages such as Python:

orgLabel = "payroll"
if orgLabel:
    print(orgLabel)

In Helm charts, you can achieve the same behavior using if blocks. Here’s an updated version of the service.yaml file that conditionally adds the organization label:

# service.yaml
apiVersion: v1
kind: Service
metadata:
  name: {{ .Release.Name }}-nginx
  {{- if .Values.orgLabel }}
  labels:
    org: {{ .Values.orgLabel }}
  {{- end }}
spec:
  ports:
    - port: 80
      name: http
  selector:
    app: hello-world

Trimming Whitespace in Templates

When Helm renders your templates, it may leave unintended whitespace between directives. To avoid this, use a dash after the opening braces—and before the closing braces, if needed—as shown below:

{{- if .Values.orgLabel }}
  labels:
    org: {{ .Values.orgLabel }}
{{- end }}

This simple trick ensures that your generated YAML files remain clean and free of extra spaces.

Using If, Else If, and Else Blocks

Helm templates support conditional logic that includes if, else if, and else constructs. Similar to Python's conditional logic, you can use helper functions such as eq for equality comparisons. Consider this Python pseudocode:

orgLabel = "payroll"

if orgLabel:
    print(orgLabel)
elif orgLabel == "hr":
    print("human resources")
else:
    print("nothing")

You can achieve similar logic in a Helm template as follows:

# service.yaml
apiVersion: v1
kind: Service
metadata:
  name: {{ .Release.Name }}-nginx
  {{- if .Values.orgLabel }}
  labels:
    org: {{ .Values.orgLabel }}
  {{- else if eq .Values.orgLabel "hr" }}
  labels:
    org: human resources
  {{- end }}
spec:
  ports:
    - port: 80
      name: http
  selector:
    app: hello-world

In this template, if orgLabel is provided, its value is used. If it specifically equals "hr", the label is set to "human resources". This approach leverages Helm's helper functions for clear and concise conditional logic.

Conditional Creation of Objects

A common use case for Helm conditionals is to control the creation of certain Kubernetes objects based on configuration. For example, you might want to create a ServiceAccount only if it is explicitly enabled in your values.yaml file.

In your default values.yaml, you can add a section like this:

# Default values for nginx-chart.
serviceAccount:
  # Specifies whether a ServiceAccount should be created
  create: true

Then, wrap the entire ServiceAccount template in a conditional block to ensure it is created only when needed:

{{- if .Values.serviceAccount.create }}
apiVersion: v1
kind: ServiceAccount
metadata:
  name: {{ .Release.Name }}-robot-sa
{{- end }}

This technique provides significant flexibility, allowing users to control which resources are deployed according to their specific requirements.

This concludes our deep dive into using conditionals in Helm charts. We demonstrated how to add optional labels, trim whitespace in rendered templates, employ if-else logic using helper functions, and conditionally create resources like service accounts. By leveraging these techniques, you can create more dynamic, efficient, and maintainable Helm charts.

Happy templating!

For more information, explore the official Helm Documentation.