Jinja2 Expressions Example

This example demonstrates Jinja2 preprocessing in kdeps workflow and resource YAML files.

Overview

Every workflow and resource YAML file is preprocessed through Jinja2 before parsing. This lets you:

• Use environment variables to conditionally configure your workflow
• Inject environment values at parse time with {{ env.VAR }}
• Use Jinja2 conditionals ({% if %}) and comments ({# ... #})

kdeps runtime API calls ({{ get(...) }}, {{ info(...) }}, {{ set(...) }}, etc.) are automatically protected from Jinja2 evaluation — you don't need {% raw %} blocks.

Workflow Structure

jinja2-expressions/
├── workflow.yaml          # Workflow with Jinja2 conditionals
└── resources/
    └── response.yaml      # Resource using runtime API + env vars

How It Works

Environment-driven configuration

# workflow.yaml
{% if env.PORT %}
  portNum: {{ env.PORT | int }}
{% else %}
  portNum: 16395
{% endif %}

Set PORT=9000 at run time to override the default port.

Auto-protected runtime API calls

In resource YAML files, kdeps API calls are automatically wrapped in {% raw %}:

# resources/response.yaml
run:
  apiResponse:
    response:
      message: "{{ info('method') }} at {{ info('current_time') }}"
      query: "{{ get('q') }}"

{{ get('q') }} and {{ info(...) }} are not evaluated by Jinja2 — they pass through unchanged and are evaluated at runtime.

Static Jinja2 expressions

Variables that don't match a kdeps API function name are evaluated by Jinja2:

# Evaluated by Jinja2 at parse time
description: "{{ env.KDEPS_APP_DESC | default('My API') }}"

Running This Example

cd examples/jinja2-expressions
kdeps run workflow.yaml --dev

Override the port via environment variable:

PORT=9000 kdeps run workflow.yaml --dev

Test with:

curl "http://localhost:16395/api/demo?q=hello"

Key Concepts

Syntax	Evaluated by	When
{{ env.VAR }}	Jinja2	Parse time
{% if env.X %}...{% endif %}	Jinja2	Parse time
{# comment #}	Jinja2	Parse time (stripped)
{{ get('x') }}	kdeps runtime	Request time
{{ info('time') }}	kdeps runtime	Request time
{{ set('k', 'v') }}	kdeps runtime	Request time