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# Templates

KUDO uses the template engine of the Go language (opens new window). Sprig template functions (opens new window) are available as well. This gives users powerful tools to parameterize operator functionality.

Templates are applied to every file in the templates directory of an operator package.

# Variables

To access the value of a variable, use {{ .Variable }}. The following variable are available for each template:

.Params

Access instance parameters defined in params.yaml. E.g., to get the value of a REPLICAS parameter, use {{ .Params.REPLICAS }}.

.OperatorName

Gets the name of the operator

.Name

Gets the name of the current instance

.Namespace

Gets the name of the instance's namespace

.Pipes

Gets pipeline parameters

.PlanName

Gets the name of the instance's active plan

.PhaseName

Gets the name of the instance's active phase

.StepName

Gets the name of the instance's active step

.AppVersion

Gets the application version

# Functions

Functions transform input like variables. Pipelines allow to use the result of a function as the input of another function. The functions provided by Go templates (opens new window) and Sprig (opens new window) allows one to

  • compare values (not, eq, ne, lt, ...)
  • make simple calculations (len, and, or, add, mul, ...)
  • manipulate text (html, js, trim, wrap, ...)

Sprig functions that allow environment access are disabled. The respective functions are env, expandenv, base, dir, clean, ext and isAbs.

Additionally, KUDO provides the following custom functions:

toYaml

Returns a YAML representation of its argument. Its output should usually be piped into | trim | indent N.

# Actions

Use actions to provide branching or repetition in templates. Below are some examples on how to use functions in operator templates. The documentation for Go templates (opens new window) has more details on its features.

# Perform arithmetic using parameters

Note that all .Params have a type of string. You may need to use a function to convert a parameter to a different type first.

This example subtracts 1 from a parameter:

{{ sub (atoi .Params.NODE_COUNT) 1 }}

# Enable or disable features using a feature parameter

This example uses an HTTPS port if the ENCRYPTION parameter is "true". Otherwise it uses an HTTP port.

spec:
  ports:
    {{ if eq .Params.ENCRYPTION "true" }}
    - name: https
      port: 443
    {{ else }}
    - name: http
      port: 80
    {{ end }}
...

# Create objects for a specified number

This example creates persistent volume claims (opens new window) for each volume.

{{ range $i, $v := until (int .Params.VOLUMES) }}
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: claim-{{ $i }}
...
{{ end }}

# Limitations

Some Kubernetes objects should not be templated. One prominent example are Jobs (opens new window). Job Spec.Template field is immutable and once the Job has been applied this field can not be changed. Trying to update Spec.Template via a templated parameter will result in an error like:

... failed to execute patch: Job.batch "xxx" is invalid: spec.template: Invalid value: core.PodTemplateSpec{...} field is immutable

A possible workaround is to delete the job (using a Delete task) and recreate it, but that is the responsibility of the operator developer.

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