Sivakumar Vunnam

Helm Templates

Oct 1, 2022 • Sivakumar Vunnam

Note that while Helm uses Go templates it does so by using the Sprig templating library which provides additional functions that you can use.

Newline Handling

{{ <something> }}              # Will produce a newline
{{- <something> }}             # Will not produce a newline

Chart Value Replacing

{{ .Values.param1 }}                   # Will insert the value of "param1" passed to your helm chart release
{{ .Values.param2 | default "abc" }}   # Insert value or default value

{{ $value1  }}                         # Will insert the value of variable "value1"

You can enforce value replacement (instead of getting empty defaults) with “required”

{{ required "Please provide mandatory 'param1'!" .Values.param1 }}

Insert complex values as YAML

{{- toYaml .Values.myhash }}
{{- toYaml (.Files.get "myconfig.yaml") | nindent 2 }}

Manipulating text

Note how string manipulation works using the pipeline operator 
{{ .Values.param | squote }}      # You usually want to single quote strings ('')
{{ .Values.param | quote }}       # You usually want to quote strings ("")
{{ .Values.param | b64enc }}      # Base64 encoding
{{ .Values.param | upper }}       # Uppercase everything
{{ .Values.param | lower }}       # Lowercase everything

{{ .Values.param | indent 16 }}   # Print with additional 16 leading spaces
{{ .Values.param | nindent 16 }}  # Ensure total indentation is 16 (useful when template code is indented)

{{ randAlphaNum 5 }}              # Produce random string 5 chars long

{{ "Hello" | repeat 3 }}          # "HelloHelloHello"

# Use format strings with printf
{{- printf "%s (%d)\n" .Values.param1 .Values.param2 .Values.param3 }}
Perform complex concatenations using pipelines in braces “( x y )” which will catch the output of the pipeline 
{{- printf "plain password: %s\nbase64 password %s\n" .Values.password (.Values.password | b64enc) }}

Accessing complex data structure

{{ .Values.hash.key1 }}        # Access single hash key

# Iterate a hash
{{- range $key, $value := .Values.myhash }}
{{- printf "key %s: value %s\n" $key $value }}
{{- end }}

# Iterate a list
{{- range .Values.mylist }}
{{- printf "list element: %s\n" . }}     # access element with "."
{{- end }}

# Grab a single value from the map by the key
{{- pluck .Values.env .Values.ip | first }} # .env is a single key, .ip is a map

Conditions

{{- if <pipeline> }}
   conditional block
{{ else }}
   other block
{{- end }}

Example pipelines to use as conditions

hasKey .Values.mymap "mykey"      # Check hash for key
gt .Values.replicaCount 2.0       # replicaCount > 2.0
lt .Values.replicaCount 5.0       # replicaCount < 5.0
eq .Values.replicaCount 1.0       # replicaCount exactly 1.0

Complex conditions using nested pipelines

not (and (hasKey .Values.mymap "mykey") (lt .Values.replicaCount 2.0))

Reading files

{{ print $.Template.BasePath "/configmap.yaml" }}

Reusing code with include

{{ include mytemplate.tpl }}   # invoke content of mytemplate.tpl right here
                               # if it produces output it will get replaced

Using variables

Save context using variable

{{- $root := . }}
{{- with .Values.something }}
   ...
   someGlobal: {{ $root.Values.someGlobal }}
{{- end }}

Defining and using functions

Define a “Hello World” function

{{- define "myfunc" }}
Hello world!
{{- end }}

and invoke it

{{ myfunc }}

our pass values

{{ myOtherFunc "scalar" }}
{{ myOtherFunc 64 }}
{{ myOtherFunc . }}           # Provide current context to pass multiple values