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Helm templating error cases

· 2 min read

Sometimes helm template error output isn't very helpful. Here are some error cases and solutions I've found in my own Helm usage.

Using printf with a variable that is a formatter string​

Usage of the variable needs to be quoted, even if the values.yaml value was quoted

values.yaml
component:
    formatString: "web-%s-%s"
deploy.yaml
{{ $name := printf (quote $formatString) $field1 $field2}}

Put quotes around numbers, especially if in Java properties​

Large numbers seem to get outputted as scientific notation sometimes. This also seems to be an open Github Issue with Helm

# values.yaml:
perInterval: 5000000 # <-- quotes needed around this int
# template:
stream.properties: |
    perInterval={{ $perInterval | default 1 }}

# output:
stream.properties: |
    perInterval=5e+06

"Expected map .. but was nil" errors / you commented stuff out​

This usually happens when you're using a values override file, eg. you have a values.yaml in chart root and are using something like helm template --values child_values.yaml

values.yaml
webservices:
    resources:
        limits:
            cpu: ..
            memory: ..
        requests: ..
    replicas: ...
component2:
    ...

If you've commented a whole "map" block like this out in some child values, Helm will think webservices == nil

child_values.yaml
webservices:
    # resources: ..
component2:

However, in a map that is defined in the parent values.yaml, you can redefine some key-value-pairs and leave out the others, and the missing key-value-pairs will get filled in as expected:

child_values.yaml
webservices:
    resources:
        requests: ..
        # "limits" key will still be readable at webservices.resources.limit
component2:

{{- -}} dash/hyphen usage when removing extra newlines / chomping whitepsace​

The helm doc section is really verbose about this. The tl;dr is that you typically only need one - character that goes on the left side:

name: ws-deploy
{{- if .biggerDeploy }}
replicas: 20
{{- end}}
label: ..

If biggerDeploy is true:

name: ws-deploy
replicas: 20
label: ..

If biggerDeploy is false:

name: ws-deploy
label: ..