A Practical Guide to Helm/

...

/

Advanced Helm Template Functions

Advanced Helm Template Functions

Get a quick overview of the most popular Helm template functions.

We'll cover the following...

Popular functions and constructs

The brackets: {{ vs {{-

If we take a closer look at our template or any other that is available on the Internet, we’ll see that sometimes opening brackets are followed by the - character, like we have in deployment.yaml—in the part responsible for injecting environment variables to a container, as shown below:

Press + to interact
env:
  {{- range .Values.app.container.env}}
   - name: {{ .key}}
     value: {{ .value}}
  {{- end}}

The purpose of it is to remove a whitespace character, including a newline character, before a template function. If we hadn’t added it here and kept a regular {{, the resulting YAML file would have looked like this:

env:
   - name: {{ .key}}
     value: {{ .value}}

The reason for this is that when generating YAML files, Helm is removing (or replacing with values) everything that is between the brackets ({{ }}). To tell Helm that we also want to remove whitespaces before a template function, we need to add the - character after the brackets ({{). And if we want to remove whitespaces after a template function, we can replace a regular bracket with -}}.

The if/elsestatements

Conditions are the essence of programming. We’ve got them in any programming language to control the flow of a running application. Therefore, it’s not a surprise that the Helm template language also has them. Here is a basic structure of an if statement in Helm:

Press + to interact
{{ if CONDITION }}
  # Do something
{{ else if OTHER CONDITION }}
  # Do something else
{{ else }}
  # Default case
{{ end }}

To visualize it as an example, let’s go back to our deployment.yaml file, and to the environment variables ...