blueprint

# Blueprint Implementation

You are helping a user work with Blueprint, a system for composing Airflow DAGs from YAML using reusable Python templates. Execute steps in order and prefer the simplest configuration that meets the user's needs.

> **Package**: `airflow-blueprint` on PyPI
> **Repo**: https://github.com/astronomer/blueprint
> **Requires**: Python 3.10+, Airflow 2.5+, Blueprint 0.2.0+

## Before Starting

Confirm with the user:
1. **Airflow version** ≥2.5
2. **Python version** ≥3.10
3. **Use case**: Blueprint is for standardized, validated templates. If user needs full Airflow flexibility, suggest writing DAGs directly or using DAG Factory instead.

---

## Determine What the User Needs

| User Request | Action |
|--------------|--------|
| "Create a blueprint" / "Define a template" | Go to **Creating Blueprints** |
| "Create a DAG from YAML" / "Compose steps" | Go to **Composing DAGs in YAML** |
| "Customize DAG args" / "Add tags to DAG" | Go to **Customizing DAG-Level Configuration** |
| "Override config at runtime" / "Trigger with params" | Go to **Runtime Parameter Overrides** |
| "Post-process DAGs" / "Add callback" | Go to **Post-Build Callbacks** |
| "Validate my YAML" / "Lint blueprint" | Go to **Validation Commands** |
| "Set up blueprint in my project" | Go to **Project Setup** |
| "Version my blueprint" | Go to **Versioning** |
| "Generate schema" / "Astro IDE setup" | Go to **Schema Generation** |
| Blueprint errors / troubleshooting | Go to **Troubleshooting** |

---

## Project Setup

If the user is starting fresh, guide them through setup:

### 1. Install the Package

```bash
# Add to requirements.txt
airflow-blueprint>=0.2.0

# Or install directly
pip install airflow-blueprint
```

### 2. Create the Loader

Create `dags/loader.py`:

```python
from blueprint import build_all

build_all()
```

DAG-level configuration (schedule, description, tags, default_args, etc.) is handled via YAML fields and `BlueprintDagArgs` templates — see **Customizing DAG-Level Configuration**.

### 3. Verify Installation

```bash
uvx --from airflow-blueprint blueprint list
```

If no blueprints found, user needs to create blueprint classes first.

---

## Creating Blueprints

When user wants to create a new blueprint template:

### Blueprint Structure

```python
# dags/templates/my_blueprints.py
from airflow.operators.bash import BashOperator
from airflow.utils.task_group import TaskGroup
from blueprint import Blueprint, BaseModel, Field

class MyConfig(BaseModel):
    # Required field with description (used in CLI output and JSON schema)
    source_table: str = Field(description="Source table name")
    # Optional field with default and validation
    batch_size: int = Field(default=1000, ge=1)

class MyBlueprint(Blueprint[MyConfig]):
    """Docstring becomes blueprint description."""

    def render(self, config: MyConfig) -> TaskGroup:
        with TaskGroup(group_id=self.step_id) as group:
            BashOperator(
                task_id="my_task",
                bash_command=f"echo '{config.source_table}'"
            )
        return group
```

### Key Rules

| Element | Requirement |
|---------|-------------|
| Config class | Must inherit from `BaseModel` |
| Blueprint class | Must inherit from `Blueprint[ConfigClass]` |
| `render()` method | Must return `TaskGroup` or `BaseOperator` |
| Task IDs | Use `self.step_id` for the group/task ID |

### Recommend Strict Validation

Suggest adding `extra="forbid"` to catch YAML typos:

```python
from pydantic import ConfigDict

class MyConfig(BaseModel):
    model_config = ConfigDict(extra="forbid")
    # fields...
```

---

## Composing DAGs in YAML

When user wants to create a DAG from blueprints:

### YAML Structure

```yaml
# dags/my_pipeline.dag.yaml
dag_id: my_pipeline
schedule: "@daily"
description: "My data pipeline"

steps:
  step_one:
    blueprint: my_blueprint
    source_table: raw.customers
    batch_size: 500

  step_two:
    blueprint: another_blueprint
    depends_on: [step_one]
    target: analytics.output
```

By default, only `schedule` and `description` are supported as DAG-level fields (via the built-in `DefaultDagArgs`). For other fields like `tags`, `default_args`, `catchup`, etc., see **Customizing DAG-Level Configuration**.

### Reserved Keys in Steps

| Key | Purpose |
|-----|---------|
| `blueprint` | Template name (required) |
| `depends_on` | List of upstream step names |
| `version` | Pin to specific blueprint version |

Everything else passes to the blueprint's config.

### Jinja2 Support

YAML supports Jinja2 templating with access to environment variables, Airflow variables/connections, and runtime context:

```yaml
dag_id: "{{ env.get('ENV', 'dev') }}_pipeline"
schedule: "{{ var.value.schedule | default('@daily') }}"

steps:
  extract:
    blueprint: extract
    output_path: "/data/{{ context.ds_nodash }}/output.csv"
    run_id: "{{ context.dag_run.run_id }}"
```

Available template variables:
- `env` — environment variables
- `var` — Airflow Variables
- `conn` — Airflow Connections
- `context` — proxy that generates Airflow template expressions for runtime macros (e.g. `context.ds_nodash`, `context.dag_run.conf`, `context.task_instance.xcom_pull(...)`)

---

## Customizing DAG-Level Configuration

By default, Blueprint supports `schedule` and `description` as DAG-level YAML fields. To use other DAG constructor arguments (tags, default_args, catchup, etc.), define a `BlueprintDagArgs` subclass.

### When to Use

- User wants `tags`, `default_args`, `catchup`, `start_date`, or any other DAG kwargs in YAML
- User wants to derive DAG properties from config (e.g. team name → owner, tier → retries)

### Defining a BlueprintDagArgs Subclass

```python
# dags/templates/my_dag_args.py
from pydantic import BaseModel
from blueprint import BlueprintDagArgs

class MyDagArgsConfig(BaseModel):
    schedule: str | None = None
    description: str | None = None
    tags: list[str] = []
    owner: str = "data-team"