prefect.cli.dev

Command line interface for working with Prefect Server

agent async

Starts a hot-reloading development agent process.

Source code in prefect/cli/dev.py

@dev_app.command()
async def agent(
    api_url: str = SettingsOption(PREFECT_API_URL),
    work_queues: List[str] = typer.Option(
        ["default"],
        "-q",
        "--work-queue",
        help="One or more work queue names for the agent to pull from.",
    ),
):
    """
    Starts a hot-reloading development agent process.
    """
    # Delayed import since this is only a 'dev' dependency
    import watchfiles

    app.console.print("Creating hot-reloading agent process...")

    try:
        await watchfiles.arun_process(
            prefect.__module_path__,
            target=agent_process_entrypoint,
            kwargs=dict(api=api_url, work_queues=work_queues),
        )
    except RuntimeError as err:
        # a bug in watchfiles causes an 'Already borrowed' error from Rust when
        # exiting: https://github.com/samuelcolvin/watchfiles/issues/200
        if str(err).strip() != "Already borrowed":
            raise

agent_process_entrypoint

An entrypoint for starting an agent in a subprocess. Adds a Rich console to the Typer app, processes Typer default parameters, then starts an agent. All kwargs are forwarded to prefect.cli.agent.start.

Source code in prefect/cli/dev.py

def agent_process_entrypoint(**kwargs):
    """
    An entrypoint for starting an agent in a subprocess. Adds a Rich console
    to the Typer app, processes Typer default parameters, then starts an agent.
    All kwargs are forwarded to  `prefect.cli.agent.start`.
    """
    import inspect

    # import locally so only the `dev` command breaks if Typer internals change
    from typer.models import ParameterInfo

    # Typer does not process default parameters when calling a function
    # directly, so we must set `start_agent`'s default parameters manually.
    # get the signature of the `start_agent` function
    start_agent_signature = inspect.signature(start_agent)

    # for any arguments not present in kwargs, use the default value.
    for name, param in start_agent_signature.parameters.items():
        if name not in kwargs:
            # All `param.default` values for start_agent are Typer params that store the
            # actual default value in their `default` attribute and we must call
            # `param.default.default` to get the actual default value. We should also
            # ensure we extract the right default if non-Typer defaults are added
            # to `start_agent` in the future.
            if isinstance(param.default, ParameterInfo):
                default = param.default.default
            else:
                default = param.default

            # Some defaults are Prefect `SettingsOption.value` methods
            # that must be called to get the actual value.
            kwargs[name] = default() if callable(default) else default

    try:
        start_agent(**kwargs)  # type: ignore
    except KeyboardInterrupt:
        # expected when watchfiles kills the process
        pass

api async

Starts a hot-reloading development API.

Source code in prefect/cli/dev.py

@dev_app.command()
async def api(
    host: str = SettingsOption(PREFECT_SERVER_API_HOST),
    port: int = SettingsOption(PREFECT_SERVER_API_PORT),
    log_level: str = "DEBUG",
    services: bool = True,
):
    """
    Starts a hot-reloading development API.
    """
    import watchfiles

    server_env = os.environ.copy()
    server_env["PREFECT_API_SERVICES_RUN_IN_APP"] = str(services)
    server_env["PREFECT_API_SERVICES_UI"] = "False"
    server_env["PREFECT_UI_API_URL"] = f"http://{host}:{port}/api"

    command = [
        sys.executable,
        "-m",
        "uvicorn",
        "--factory",
        "prefect.server.api.server:create_app",
        "--host",
        str(host),
        "--port",
        str(port),
        "--log-level",
        log_level.lower(),
    ]

    app.console.print(f"Running: {' '.join(command)}")
    import signal

    stop_event = anyio.Event()
    start_command = partial(
        run_process, command=command, env=server_env, stream_output=True
    )

    async with anyio.create_task_group() as tg:
        try:
            server_pid = await tg.start(start_command)
            async for _ in watchfiles.awatch(
                prefect.__module_path__,
                stop_event=stop_event,  # type: ignore
            ):
                # when any watched files change, restart the server
                app.console.print("Restarting Prefect Server...")
                os.kill(server_pid, signal.SIGTERM)  # type: ignore
                # start a new server
                server_pid = await tg.start(start_command)
        except RuntimeError as err:
            # a bug in watchfiles causes an 'Already borrowed' error from Rust when
            # exiting: https://github.com/samuelcolvin/watchfiles/issues/200
            if str(err).strip() != "Already borrowed":
                raise
        except KeyboardInterrupt:
            # exit cleanly on ctrl-c by killing the server process if it's
            # still running
            try:
                os.kill(server_pid, signal.SIGTERM)  # type: ignore
            except ProcessLookupError:
                # process already exited
                pass

            stop_event.set()

build_docs

Builds REST API reference documentation for static display.

Source code in prefect/cli/dev.py

@dev_app.command()
def build_docs(
    schema_path: str = None,
):
    """
    Builds REST API reference documentation for static display.
    """
    exit_with_error_if_not_editable_install()

    from prefect.server.api.server import create_app

    schema = create_app(ephemeral=True).openapi()

    if not schema_path:
        schema_path = (
            prefect.__development_base_path__ / "docs" / "api-ref" / "schema.json"
        ).absolute()
    # overwrite info for display purposes
    schema["info"] = {}
    with open(schema_path, "w") as f:
        json.dump(schema, f)
    app.console.print(f"OpenAPI schema written to {schema_path}")

build_image

Build a docker image for development.

Source code in prefect/cli/dev.py

@dev_app.command()
def build_image(
    arch: str = typer.Option(
        None,
        help=(
            "The architecture to build the container for. "
            "Defaults to the architecture of the host Python. "
            f"[default: {platform.machine()}]"
        ),
    ),
    python_version: str = typer.Option(
        None,
        help=(
            "The Python version to build the container for. "
            "Defaults to the version of the host Python. "
            f"[default: {python_version_minor()}]"
        ),
    ),
    flavor: str = typer.Option(
        None,
        help=(
            "An alternative flavor to build, for example 'conda'. "
            "Defaults to the standard Python base image"
        ),
    ),
    dry_run: bool = False,
):
    """
    Build a docker image for development.
    """
    exit_with_error_if_not_editable_install()
    # TODO: Once https://github.com/tiangolo/typer/issues/354 is addressed, the
    #       default can be set in the function signature
    arch = arch or platform.machine()
    python_version = python_version or python_version_minor()

    tag = get_prefect_image_name(python_version=python_version, flavor=flavor)

    # Here we use a subprocess instead of the docker-py client to easily stream output
    # as it comes
    command = [
        "docker",
        "build",
        str(prefect.__development_base_path__),
        "--tag",
        tag,
        "--platform",
        f"linux/{arch}",
        "--build-arg",
        "PREFECT_EXTRAS=[dev]",
        "--build-arg",
        f"PYTHON_VERSION={python_version}",
    ]

    if flavor:
        command += ["--build-arg", f"BASE_IMAGE=prefect-{flavor}"]

    if dry_run:
        print(" ".join(command))
        return

    try:
        subprocess.check_call(command, shell=sys.platform == "win32")
    except subprocess.CalledProcessError:
        exit_with_error("Failed to build image!")
    else:
        exit_with_success(f"Built image {tag!r} for linux/{arch}")

container

Run a docker container with local code mounted and installed.

Source code in prefect/cli/dev.py

@dev_app.command()
def container(bg: bool = False, name="prefect-dev", api: bool = True, tag: str = None):
    """
    Run a docker container with local code mounted and installed.
    """
    exit_with_error_if_not_editable_install()
    import docker
    from docker.models.containers import Container

    client = docker.from_env()

    containers = client.containers.list()
    container_names = {container.name for container in containers}
    if name in container_names:
        exit_with_error(
            f"Container {name!r} already exists. Specify a different name or stop "
            "the existing container."
        )

    blocking_cmd = "prefect dev api" if api else "sleep infinity"
    tag = tag or get_prefect_image_name()

    container: Container = client.containers.create(
        image=tag,
        command=[
            "/bin/bash",
            "-c",
            (  # noqa
                "pip install -e /opt/prefect/repo\\[dev\\] && touch /READY &&"
                f" {blocking_cmd}"
            ),
        ],
        name=name,
        auto_remove=True,
        working_dir="/opt/prefect/repo",
        volumes=[f"{prefect.__development_base_path__}:/opt/prefect/repo"],
        shm_size="4G",
    )

    print(f"Starting container for image {tag!r}...")
    container.start()

    print("Waiting for installation to complete", end="", flush=True)
    try:
        ready = False
        while not ready:
            print(".", end="", flush=True)
            result = container.exec_run("test -f /READY")
            ready = result.exit_code == 0
            if not ready:
                time.sleep(3)
    except BaseException:
        print("\nInterrupted. Stopping container...")
        container.stop()
        raise

    print(
        textwrap.dedent(
            f"""
            Container {container.name!r} is ready! To connect to the container, run:

                docker exec -it {container.name} /bin/bash
            """
        )
    )

    if bg:
        print(
            textwrap.dedent(
                f"""
                The container will run forever. Stop the container with:

                    docker stop {container.name}
                """
            )
        )
        # Exit without stopping
        return

    try:
        print("Send a keyboard interrupt to exit...")
        container.wait()
    except KeyboardInterrupt:
        pass  # Avoid showing "Abort"
    finally:
        print("\nStopping container...")
        container.stop()

kubernetes_manifest

Generates a Kubernetes manifest for development.

Example

$ prefect dev kubernetes-manifest | kubectl apply -f -

Source code in prefect/cli/dev.py

@dev_app.command()
def kubernetes_manifest():
    """
    Generates a Kubernetes manifest for development.

    Example:
        $ prefect dev kubernetes-manifest | kubectl apply -f -
    """
    exit_with_error_if_not_editable_install()

    template = Template(
        (
            prefect.__module_path__ / "cli" / "templates" / "kubernetes-dev.yaml"
        ).read_text()
    )
    manifest = template.substitute(
        {
            "prefect_root_directory": prefect.__development_base_path__,
            "image_name": get_prefect_image_name(),
        }
    )
    print(manifest)

start async

Starts a hot-reloading development server with API, UI, and agent processes.

Each service has an individual command if you wish to start them separately. Each service can be excluded here as well.

Source code in prefect/cli/dev.py

@dev_app.command()
async def start(
    exclude_api: bool = typer.Option(False, "--no-api"),
    exclude_ui: bool = typer.Option(False, "--no-ui"),
    exclude_agent: bool = typer.Option(False, "--no-agent"),
    work_queues: List[str] = typer.Option(
        ["default"],
        "-q",
        "--work-queue",
        help="One or more work queue names for the dev agent to pull from.",
    ),
):
    """
    Starts a hot-reloading development server with API, UI, and agent processes.

    Each service has an individual command if you wish to start them separately.
    Each service can be excluded here as well.
    """
    async with anyio.create_task_group() as tg:
        if not exclude_api:
            tg.start_soon(
                partial(
                    api,
                    host=PREFECT_SERVER_API_HOST.value(),
                    port=PREFECT_SERVER_API_PORT.value(),
                )
            )
        if not exclude_ui:
            tg.start_soon(ui)
        if not exclude_agent:
            # Hook the agent to the hosted API if running
            if not exclude_api:
                host = f"http://{PREFECT_SERVER_API_HOST.value()}:{PREFECT_SERVER_API_PORT.value()}/api"  # noqa
            else:
                host = PREFECT_API_URL.value()
            tg.start_soon(agent, host, work_queues)

ui async

Starts a hot-reloading development UI.

Source code in prefect/cli/dev.py

@dev_app.command()
async def ui():
    """
    Starts a hot-reloading development UI.
    """
    exit_with_error_if_not_editable_install()
    with tmpchdir(prefect.__development_base_path__ / "ui"):
        app.console.print("Installing npm packages...")
        await run_process(["npm", "install"], stream_output=True)

        app.console.print("Starting UI development server...")
        await run_process(command=["npm", "run", "serve"], stream_output=True)