The difference between the two functions is that the result of template cannot be chained with another function, while include can.

Please note that the template function is included in the Go language, while the include function is only available in Helm.

Here is an example Helm template:

{{- define "greet" }}hello {{ . }}{{- end }}
---
greetInclude: {{ include "greet" .Values.name | title }}
greetTemplate: {{ template "greet" .Values.name | title }}

Feeding in these values:

---
name: johnny

This is the output:

---
greetInclude: Hello Johnny
greetTemplate: hello Johnny

Notice that the title function, which capitalizes the words passed in, is getting the whole output of the greet definition, when using include.

When using template, the function is only receiving the value of .Values.name. That’s is why include is capitalizing both words Hello Johnny, while template only the second word.

If we wanted to, we could make include behave like template if we put some extra parenthesis:

{{- define "greet" }}hello {{ . }}{{- end }}

---
greetInclude: {{ include "greet" (.Values.name | title) }}
greetTemplate: {{ template "greet" .Values.name | title }}

Which would result in a identical output:

---
greetInclude: hello Johnny
greetTemplate: hello Johnny