Supported Templating Languages Enterprise

The following templating languages are supported:

• envsubst (default)
• templating

Declare the templating language to be used to render the template by setting spec.renderType.

Envsubst

envsubst, which is short for 'environment substitution', uses envsubst for rendering. This templating format is used by clusterctl.

Variables can be set for rendering into the template in the ${VAR_NAME} syntax.

Supported Functions

Expression	Meaning
${var}	Value of $var
${#var}	String length of $var
${var^}	Uppercase first character of $var
${var^^}	Uppercase all characters in $var
${var,}	Lowercase first character of $var
${var,,}	Lowercase all characters in $var
${var:n}	Offset $var n characters from start
${var:n:len}	Offset $var n characters with max length of len
${var#pattern}	Strip shortest pattern match from start
${var##pattern}	Strip longest pattern match from start
${var%pattern}	Strip shortest pattern match from end
${var%%pattern}	Strip longest pattern match from end
${var-default}	If $var is not set, evaluate expression as $default
${var:-default}	If $var is not set or is empty, evaluate expression as $default
${var=default}	If $var is not set, evaluate expression as $default
${var:=default}	If $var is not set or is empty, evaluate expression as $default
${var/pattern/replacement}	Replace as few pattern matches as possible with replacement
${var//pattern/replacement}	Replace as many pattern matches as possible with replacement
${var/#pattern/replacement}	Replace pattern match with replacement from $var start
${var/%pattern/replacement}	Replace pattern match with replacement from $var end

Templating

Templating uses text/templating for rendering, using go-templating style syntax {{ .params.CLUSTER_NAME }} where params are provided by the .params variable. Template functions can also be used with the syntax {{ .params.CLUSTER_NAME | FUNCTION }}.

Supported Functions

As taken (from the Sprig library)

Function Type	Functions
String Functions	trim, wrap, randAlpha, plural
String List Functions	splitList, sortAlpha
Integer Math Functions	add, max, mul
Integer Slice Functions	until, untilStep
Float Math Functions	addf, maxf, mulf
Date Functions	now, date
Defaults Functions	default, empty, coalesce, fromJson, toJson, toPrettyJson, toRawJson, ternary
Encoding Functions	b64enc, b64dec
Lists and List Functions	list, first, uniq
Dictionaries and Dict Functions	get, set, dict, hasKey, pluck, dig, deepCopy
Type Conversion Functions	atoi, int64, toString
Flow Control Functions	fail
UUID Functions	uuidv4
Version Comparison Functions	semver, semverCompare
Reflection	typeOf, kindIs, typeIsLike

Custom Delimiters

The default delimiters for renderType: templating are {{ and }}. These can be changed by setting the templates.weave.works/delimiters annotation on the template. For example:

• templates.weave.works/delimiters: "{{,}}" - default
• templates.weave.works/delimiters: "${{,}}"
  • Use ${{ and }}, for example "${{ .params.CLUSTER_NAME }}"
  • Useful as {{ in yaml is invalid syntax and needs to be quoted. If you need to provide a un-quoted number value like replicas: 3 you should use these delimiters.
    • ❌ replicas: {{ .params.REPLICAS }} Invalid yaml
    • ❌ replicas: "{{ .params.REPLICAS }}" Valid yaml, incorrect type. The type is a string not a number and will fail validation.
    • ✅ replicas: ${{ .params.REPLICAS }} Valid yaml and correct number type.
• templates.weave.works/delimiters: "<<,>>"
  • Use << and >>, for example << .params.CLUSTER_NAME >>
  • Useful if you are nesting templates and need to differentiate between the delimiters used in the inner and outer templates.