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About Template Functions

This topic describes Replicated template functions, including information about template function contexts, syntax, and examples.

Overview of Template Functions​

You can use Go template functions in your application manifest files to render the manifests in the customer environment. Replicated also provides a set of custom template functions based on the Go text/template library. You can use all functionality of Go templating language with the Replicated custom template functions.

For more information about the Go library, see text/template in the Go documentation. For more information about Replicated template functions, see Replicated Template Function Contexts below.

A common use case for adding template functions to your application manifest files is to generate values that are specific to the customer environment, such as customer entitlement information or user-provided configurations. Similarly, template functions can also return values with information about the customer environment, such the number of nodes detected in the Kubernetes cluster where the application is installed.

For example, you can create a custom entitlement in Replicated vendor portal named max_concurrent_users that defines the maximum number of concurrent users permitted by the customer's license. To enforce the entitlement, you can use a template function in the License context to supply the max_concurrent_users value as a Pod environment variable:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: api
spec:
  selector:
    matchLabels:
      app: api
  template:
    spec:
      containers:
      - image: myapp/api:v1.0.1
        name: api
        env:
          - name: MAX_CONCURRENT_USERS
            value: '{{repl LicenseFieldValue "max_concurrent_users" }}'

For more information about using template functions to create custom license fields, see Managing Custom License Fields.

About Templating and Variables​

Replicated templates all manifest files, except the Config custom resource, at the same time during a single process. For the Config custom resource, Replicated templates each of the configuration fields defined in the items: field separately.

Template functions have access to variables defined in other manifest files that are templated at the same time. This means that you can assign the result returned by a template function to a variable in a manifest file, then use the variable in another template function.

Template functions in the Config custom resource do not have access to variables defined in other configuration fields under items:. For information about how to use hidden fields to pass variables to template functions in the Config custom resource, see Example: Using Variables to Generate TLS Certificates and Keys in Config Context.

Template Function Syntax​

You can assign a template function as the value for a field in a manifest file. You include template functions in manifest files as strings, using the syntax described in this section.

The Replicated template function syntax supports the following functionally equivalent delimiters:

  • '{{repl ... }}': This syntax includes quotation marks to be valid YAML and renders a string value.
  • repl{{ ... }}: This syntax renders an integer value.

'{{repl ... }}'​

Syntax
'{{repl ... }}'
Description

This syntax is wrapped in quotes because {{ is not a valid beginning for a string in YAML. To use a template function with this syntax as a value in a YAML file, you must wrap it in quotation marks.

This syntax renders string values. Do not use this syntax if the Kubernetes API field requires an integer value.

Example
env:
  - name: MAX_CONCURRENT_USERS
    value: '{{repl LicenseFieldValue "max_concurrent_users"}}'

The template function above renders as a string. For example:

env:
  - name: MAX_CONCURRENT_USERS
    value: '100'

repl{{ ... }}​

Syntax
repl{{ ... }}
Description

This syntax uses the delimiter after repl, and does not require quotation marks. Use this syntax to render integer values.

Example
replicas: repl{{ ConfigOption "replicas" }}

The template function above renders as an integer. For example:

replicas: 5

Replicated Template Function Contexts​

Replicated template functions are grouped into different contexts, depending on the phase of the application lifecycle when the function is available and the context data that is provided.

Static Context​

You can use template functions in the static context in any manifest file. Static context template functions are available at any time.

The static context also includes the Masterminds Sprig function library. For more information, see Sprig Function Documentation on the sprig website.

For a list of all Replicated template functions available in the static context, see Static context.

Config Context​

Template functions in the config context are available when rendering an application that has a config screen. At execution time, template functions in this context also can use the static context functions.

For a list of all Replicated template functions available in the config context, click see Config context.

License Context​

Template functions in the license context have access to license and version data.

For a list of all Replicated functions available in the license context, see License context.

kURL Context​

Template functions in the kURL context have access to information about applications installed on a cluster created by the Replicated Kubernetes installer.

For a list of all Replicated template functions available in the kURL context, see kURL context.

Identity Context​

Template functions in the Identity context have access to Replicated identity service information.

For a list of all Replicated template functions available in the identity context, see Identity context.