Helm Charts - How do I use `default` on undefined object property values?

Question

Using Helm, I was under the impression default would be the fallback if a variable is not defined. However, it doesn't appear Helm can get to values in sub-object hashes:

  type: {{ default "NodePort" .Values.fpm.service.type }}

If .Values.fpm.service or service.type is not defined, it should use 9000.

However, attempting to template this throws a nil pointer error:

 <.Values.fpm.service.type>: nil pointer evaluating interface {}.type

Is there a way to simply perform this level of variable testing? Or am I subjected to an if/else test?

The intent of this is to optionally define .fpm.service (and [..].type) within your values.yaml file.

(I'm building a Helm Library chart to handle optional definitions by main charts)

Granulite

Answer 1

According to the official Helm doc (Using Default Function), the syntax is different and you should use it this way:

type: {{ .Values.fpm.service.type | default "NodePort" | quote }}

Dockery

That's not it, though. The issue isn't around default. The issue is around Helm trying to go down into a non-existing object: checking for "fpm.service.type" and not just stopping when "fpm.service" doesn't exist. – Granulite

PS: The docs to clearly state this is an expected argument approach, too: default DEFAULT_VALUE GIVEN_VALUE – Granulite

This answer doesn't answer the question at all. – Wavy

.Values.nonexiting | default "a default" will work. .Values.nonexisting.nonexting2 | default "default" will not. Due to the fact that "nonexisting" does not exist and Helm cant then go deeper – Ferricyanide

There's an option to wrap it with brackets for example: type: {{ ((.Values.fpm).service).type | default "NodePort" | quote }} – Milone

Answer 2

Doesn't look like there's really a good way to stop Helm from trying to dive into non-existing objects. I moved into a single line if condition, and it worked:

  type: {{ if .Values.fpm.service -}} {{ .default "NodePort" .Values.fpm.service.type | quote }} {{- else -}} "NodePort" {{- end }}

This way, I check if fpm.service exists first, before trying .type check. It works, whether .service and .service.type is or is not defined.

Granulite

You are correct, non existing objects are being traversed, at least we have to define them with empty values. – Urdu

Answer 3

In Helm we can wrap a value that we might consider optional in brackets.

type: {{ (.Values.fpm.service).type | default "NodePort" }}

Now when we try to run a helm template / install, it will consider .Values.fpm.service to be optional. We would still run into a Nil pointer if .Values.fpm is not set. So you must ensure to encapsulate up until where should be considered optional, as you can see in the example I provided, I did not place brackets around .type otherwise, it would try to find service which may not exist.

Skuld

See also https://mcmap.net/q/271951/-how-to-make-nested-variables-optional-in-helm – Spagyric

great answer! works like a charm without ugly syntax or overcomplicated statements. – Ulysses

This works! stupid helm charts – Elurd