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Values

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

Naming Conventions

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

Correct:

chicken: true
chickenNoodleSoup: true

Incorrect:

Chicken: true  # initial caps may conflict with built-ins
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 to easily 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:

server:
  name: nginx
  port: 80

Flat:

serverName: nginx
serverPort: 80

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

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

{{ if .Values.server }}
  {{ default "none" .Values.server.name }}
{{ end }}

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

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

When there are a large number of related variables, and at least one of them is non-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: 12345678 will 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 your integers as strings as well, and use {{ int $value }} in the template to convert from a string back to an integer.

In most cases, explicit type tags are respected, so foo: !!string 1234 should treat 1234 as a string. However, the YAML parser consumes tags, so the type data 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 or helm upgrade

When designing the structure of your values, keep in mind that users of your chart may want to override them via either the -f flag or with the --set option.

Since --set is more limited in expressiveness, the first guidelines for writing 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:

servers:
  - name: foo
    port: 80
  - name: bar
    port: 81

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

Easy to use:

servers:
  foo:
    port: 80
  bar:
    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 documentation string should begin with the name of the property that it describes, and then give at least a one-sentence description.

Incorrect:

# the host name for the webserver
serverHost = example
serverPort = 9191

Correct:

# serverHost is the host name for the webserver
serverHost = example
# serverPort is the HTTP listener port for the webserver
serverPort = 9191

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