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Helm template

Built-in objects

  • Built-in objects always begin with capital letter (Go naming convention)

Release

  • Release: describes the release itself
  • Release.Name: release name
  • Release.Namespace: namespace to be released into
  • Release.IsUpgrade: set to true if the current operation is an upgrade or rollback
  • Release.IsInstall: set to true if the current operation is an install
  • Release.Revision: revision number for this release. On install, this is 1, and it is incremented with each upgrade and rollback.
  • Release.Service: The service that is rendering the present template. On Helm, this is always Helm.
apiVersion: v1
kind: ConfigMap
metadata:
  name: {{ .Release.Name }}-configmap
data:
  myvalue: "Hello World"

Values

  • Values: object structure defined in values.yaml

Chart

  • Chart: contents of the Chart.yaml file

Files

  • Files: access to non-special files in a chart
  • Files.Get: function for getting a file by name (.Files.Get config.ini)
  • Files.GetBytes function for getting the contents of a file as an array of bytes instead of as a string. This is useful for things like images.
  • Files.Glob: function that returns a list of files whose names match the given shell glob pattern.
  • Files.Lines: function that reads a file line-by-line. This is useful for iterating over each line in a file.
  • Files.AsSecrets: function that returns the file bodies as Base 64 encoded strings.
  • Files.AsConfig: function that returns file bodies as a YAML map.

Capabilities

  • Capabilities: provides information about what capabilities the Kubernetes cluster supports
  • Capabilities.APIVersions: is a set of versions.
  • Capabilities.APIVersions.Has: $version indicates whether a version (e.g., batch/v1) or resource (e.g., apps/v1/Deployment) is available on the cluster.
  • Capabilities.KubeVersion and Capabilities.KubeVersion.Version is the Kubernetes version.
  • Capabilities.KubeVersion.Major: is the Kubernetes major version.
  • Capabilities.KubeVersion.Minor: is the Kubernetes minor version.
  • Capabilities.HelmVersion: is the object containing the Helm Version details, it is the same output of helm version
  • Capabilities.HelmVersion.Version: is the current Helm version in semver format.
  • Capabilities.HelmVersion.GitCommit: is the Helm git sha1.
  • Capabilities.HelmVersion.GitTreeState: is the state of the Helm git tree.
  • Capabilities.HelmVersion.GoVersion: is the version of the Go compiler used.

Template

  • Template: contains information about the current template that is being executed
  • Template.Name: A namespaced file path to the current template (e.g. mychart/templates/mytemplate.yaml)
  • Template.BasePath: The namespaced path to the templates directory of the current chart (e.g. mychart/templates)

Functions

  • quote: add quotes to the value {{ quote .Values.favorite.food }} or {{ .Values.favorite.food | quote }}
  • lookup: return a resource in the template {{ lookup "v1" "Pod" "mynamespace" "mypod" }}
  • range {{ range $index, $service := (lookup "v1" "Service" "mynamespace" "").items }} {{/ do something with each service /}} {{ end }}

Logic and Control Flow

  • and: returns a boolean of two arguments {{ and .Arg1 .Arg2 }}
  • or: {{ or .Arg1 .Arg2 }}
  • not: {{ not .Arg }}
  • eq: {{ eq .Arg1 .Arg2 }}
  • ne: {{ ne .Arg1 .Arg2 }}
  • lt: {{ lt .Arg1 .Arg2 }}
  • gt: {{ gt .Arg1 .Arg2 }}
  • ge: {{ ge .Arg1 .Arg2 }}
  • empty: true is the value is empty {{ empty .Foo }}
  • default: set a default value {{ .Values.favorite.drink | default (printf "%s-tea" (include "fullname" .)) }}
  • fail: unconditionally returns error {{ fail "Please accept the end user license agreement"}}
  • coalesce: takes a list and returns the first non-empty {{ coalesce 0 1 2 }} returns 1 {{ coalesce .name .parent.name "Matt" }} returns matt if the others are empty
  • ternary: {{ true | ternary "foo" "bar"}} returns foo {{ false | ternary "foo" "bar"}} retruns bar

String Functions

  • print: {{ print "Matt has " .Dogs " dogs"}}
  • println: adds a newline
  • printf: {{ printf "%s has %d dogs." .Name .NumberDogs }}
  • trim: {{ trim " hello " }}
  • trimAll: {{ trimAll "$" "$5.00" }} returns 5.00
  • trimPrefix: {{ trimPrefix "-" "-hello" }} returns hello
  • trimSuffix: {{ trimSuffix "-" "hello-" }} returns hello
  • lower: {{ lower "HELLO" }}
  • upper: {{ upper "hello" }}
  • title: {{ title "hello world" }} returns Hello World
  • untitle: {{ untitle "Hello World" }} returns hello world
  • repeat: {{ repeat 2 "hello" }} returns hellohello
  • substr: {{ substr 0 5 "hello world" }} returns hello
  • nospace: {{ nospace "hello w o r l d" }} returns helloworld
  • trunc: {{ trunc 5 "hello world" }} returns hello {{ trunc -5 "hello world" }} returns world
  • abbrev: truncate with ellipses (...) {{ abbrev 5 "hello world" }} returns he...
  • abbrevboth: truncate both sides {{ abbrevboth 5 10 "1234 5678 9123" }} returns ...5678...
  • initials: {{ initials "First Try" }} returns FT
  • randAlphaNum: uses 0-9a-zA-Z {{ randNumeric 3 }}
  • randAlpha uses a-zA-Z
  • randNumeric uses 0-9
  • randAscii uses all printable ASCII characters
  • wrap: {{ wrap 80 $someText }} wrap the string in 80 columns (creates a list)
  • wrapWith: {{ wrapWith 5 "\t" "Hello World" }}
  • contains: {{ contains "cat" "catch" }} returns true

Flow Control

If/Else

  • a false is a boolean false, numeric 0, empty string, nil, empty collection (map, slice, tuple, dict, array)
apiVersion: v1
kind: ConfigMap
metadata:
  name: {{ .Release.Name }}-configmap
data:
  myvalue: "Hello World"
  drink: {{ .Values.favorite.drink | default "tea" | quote }}
  food: {{ .Values.favorite.food | upper | quote }}
  {{- if eq .Values.favorite.drink "coffee" }} # {{- consumes new lines on the left
  mug: "true"
  {{- end }}

With

apiVersion: v1
kind: ConfigMap
metadata:
  name: {{ .Release.Name }}-configmap
data:
  myvalue: "Hello World"
  {{- with .Values.favorite }} # uses scope .Values.favorite (inside this block .drink and .food may be mentioned directly)
  drink: {{ .drink | default "tea" | quote }}
  food: {{ .food | upper | quote }}
  release: {{ $.Release.Name }} # $ is a reference to the root scope
  {{- end }}

Range

  • range can be used over list, tuple, map or dict
pizzaToppings:
  - mushrooms
  - cheese
  - peppers
  - onions
favorite:
  a: b
  c: d

apiVersion: v1
kind: ConfigMap
metadata:
  name: {{ .Release.Name }}-configmap
data:
  myvalue: "Hello World"

  # predefined list
  toppings: |-
    {{- range .Values.pizzaToppings }}
    - {{ . | title | quote }}
    {{- end }}

  # dinamic list
  sizes: |-
    {{- range tuple "small" "medium" "large" }}
    - {{ . }}
    {{- end }}

  # iterate list
  toppings: |-
    {{- range $index, $topping := .Values.pizzaToppings }}
      {{ $index }}: {{ $topping }}
    {{- end }}

  # iterate object
  {{- range $key, $val := .Values.favorite }}
  {{ $key }}: {{ $val | quote }}
  {{- end }}

Variables

  • Variables can be created using := operator
apiVersion: v1
kind: ConfigMap
metadata:
  name: {{ .Release.Name }}-configmap
data:
  myvalue: "Hello World"
  {{- $relname := .Release.Name -}}
  release: {{ $relname }}