Values

This part of the best practices guide covers using values. In this part of theguide, we provide recommendations on how you should structure and use yourvalues, with focus on designing a chart’s values.yaml file.

Naming Conventions

Variables names should begin with a lowercase letter, and words should beseparated with camelcase:

Correct:

  1. chicken: true
  2. chickenNoodleSoup: true

Incorrect:

  1. Chicken: true  # initial caps may conflict with built-ins
  2. chicken-noodle-soup: true # do not use hyphens in the name

Note that all of Helm’s built-in variables begin with an uppercase letter toeasily distinguish them from user-defined values: .Release.Name,.Capabilities.KubeVersion.

Flat or Nested Values

YAML is a flexible format, and values may be nested deeply or flattened.

Nested:

  1. server:
  2.   name: nginx
  3.   port: 80

Flat:

  1. serverName: nginx
  2. serverPort: 80

In most cases, flat should be favored over nested. The reason for this is thatit is simpler for template developers and users.

For optimal safety, a nested value must be checked at every level:

  1. {{ if .Values.server }}
  2.   {{ default "none" .Values.server.name }}
  3. {{ end }}

For every layer of nesting, an existence check must be done. But for flatconfiguration, such checks can be skipped, making the template easier to readand use.

  1. {{ default "none" .Values.serverName }}

When there are a large number of related variables, and at least one of them isnon-optional, nested values may be used to improve readability.

Make Types Clear

YAML’s type coercion rules are sometimes counterintuitive. For example, foo:false is not the same as foo: "false". Large integers like foo: 12345678will get converted to scientific notation in some cases.

The easiest way to avoid type conversion errors is to be explicit about strings,and implicit about everything else. Or, in short, quote all strings.

Often, to avoid the integer casting issues, it is advantageous to store yourintegers as strings as well, and use {{ int $value }} in the template toconvert from a string back to an integer.

In most cases, explicit type tags are respected, so foo: !!string 1234 shouldtreat 1234 as a string. However, the YAML parser consumes tags, so the typedata is lost after one parse.

Consider How Users Will Use Your Values

There are three potential sources of values:

  • A chart’s values.yaml file
  • A values file supplied by helm install -f or helm upgrade -f
  • The values passed to a —set or —set-string flag on helm install orhelm upgradeWhen designing the structure of your values, keep in mind that users of yourchart may want to override them via either the -f flag or with the —setoption.

Since —set is more limited in expressiveness, the first guidelines forwriting your values.yaml file is make it easy to override from —set.

For this reason, it’s often better to structure your values file using maps.

Difficult to use with —set:

  1. servers:
  2.   - name: foo
  3.     port: 80
  4.   - name: bar
  5.     port: 81

The above cannot be expressed with —set in Helm <=2.4. In Helm 2.5, theaccessing the port on foo is —set servers[0].port=80. Not only is it harderfor the user to figure out, but it is prone to errors if at some later time theorder of the servers is changed.

Easy to use:

  1. servers:
  2.   foo:
  3.     port: 80
  4.   bar:
  5.     port: 81

Accessing foo’s port is much more obvious: —set servers.foo.port=80.

Document values.yaml

Every defined property in values.yaml should be documented. The documentationstring should begin with the name of the property that it describes, and thengive at least a one-sentence description.

Incorrect:

  1. # the host name for the webserver
  2. serverHost: example
  3. serverPort: 9191

Correct:

  1. # serverHost is the host name for the webserver
  2. serverHost: example
  3. # serverPort is the HTTP listener port for the webserver
  4. serverPort: 9191

Beginning each comment with the name of the parameter it documents makes it easyto grep out documentation, and will enable documentation tools to reliablycorrelate doc strings with the parameters they describe.