17_adding_api_endpoints.rst

Adding a New API Endpoint in Apache Airflow

This documentation outlines the steps required to add a new API endpoint in Apache Airflow. It includes implementing the logic, running pre-commit checks, and documenting the changes.

The outline for this document in GitHub is available at top-right corner button (with 3-dots and 3 lines).

Introduction

The source code for the RestAPI is located under api_fastapi/core_api. Endpoints are located under api_fastapi/core_api/routes and contains different types of endpoints. The main two are public and ui. Public endpoints are part of the public API, standardized, well documented and most importantly backward compatible. UI endpoints are custom endpoints made for the frontend that do not respect backward compatibility i.e they can be adapted at any time for UI needs. When adding an endpoint you should try as much as possible to make it reusable by the community, have a stable design in mind, standardized and therefore part of the public API. If this is not possible because the data types are too specific or subject to frequent change then adding it to the UI endpoints is more suitable.

Step 1: Implement the Endpoint Logic

1. Considering the details above decide whether your endpoints should be part of the public or ui interface.
2. Navigate to the appropriate routes directory in api_fastapi/core_api/routes.
3. Register a new route for your endpoint with the appropriate HTTP method, query params, permissions, body type, etc.
4. Specify the appropriate Pydantic type in the return type annotation.

Example:

@dags_router.get("/dags")  # permissions go in the dependencies parameter here
async def get_dags(
    *,
    limit: int = 100,
    offset: int = 0,
    tags: Annotated[list[str] | None, Query()] = None,
    dag_id_pattern: str | None = None,
    only_active: bool = True,
    paused: bool | None = None,
    order_by: str = "dag_id",
    session: SessionDep,
) -> DAGCollectionResponse:
    pass

Step 2: Add tests for your Endpoints

1. Verify manually with a local API that the endpoint behaves as expected.
2. Go to the test folder and initialize new tests.
3. Implements extensive tests to validate query param, permissions, error handling etc.

Step 3: Documentation

Documentation is built automatically by FastAPI and our pre-commit hooks. Verify by going to /docs that the documentation is clear and appears as expected (body and return types, query params, validation)

Step 4: Run Pre-commit Hooks

1. Ensure all code meets the project's quality standards by running pre-commit hooks.
2. Pre-commit hooks include static code checks, formatting, and other validations.
3. Persisted openapi spec is located in v1-generated.yaml and a hook will take care of updating it based on your new endpoint, you just need to add and commit the change.
4. Run the following command to execute all pre-commit hooks:

pre-commit run --all-files

Optional: Adding Pydantic Model

In some cases, you may need to define additional models for new data structures. For example, if you are adding an endpoint that involves new data objects or collections, you may define a model in a Python file. The model will be used to validate and serialize/deserialize objects. Here's an example:

class DAGModelResponse(BaseModel):
    """DAG serializer for responses."""

    dag_id: str
    dag_display_name: str
    is_paused: bool
    is_active: bool
    last_parsed_time: datetime | None

These models are defined to structure and validate the data handled by the API. Once defined, these models will automatically be added to the OpenAPI spec file as long as they are actually used by one endpoint.

After adding or modifying Pydantic models, make sure to run the pre-commit hooks again to update any generated files.

Situational: Legacy Endpoint Migration

When migrating legacy endpoint to the new FastAPI API:

1. Implement a feature complete endpoint in comparison to the legacy one or explain why this is not possible in your context.
2. Make sure to have a good test coverage by copying over the legacy test cases to the new endpoint. This will guarantee an isofunctional new endpoint.
3. Mark the legacy endpoint with the @mark_fastapi_migration_done decorator. This will help maintainers keep track of the endpoints remaining for the migration and those already migrated.