_function_client.py

# Copyright 2023 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


from __future__ import annotations

import inspect
import logging
import os
import random
import shutil
import string
import tempfile
import textwrap
import types
from typing import Any, cast, Optional, Sequence, Tuple, TYPE_CHECKING
import warnings

import requests

import bigframes.exceptions as bfe
import bigframes.formatting_helpers as bf_formatting
import bigframes.functions.function_template as bff_template

if TYPE_CHECKING:
    from bigframes.session import Session

import google.api_core.exceptions
import google.api_core.retry
from google.cloud import bigquery, functions_v2

from . import _utils

logger = logging.getLogger(__name__)

# https://cloud.google.com/sdk/gcloud/reference/functions/deploy#--ingress-settings
_INGRESS_SETTINGS_MAP = types.MappingProxyType(
    {
        "all": functions_v2.ServiceConfig.IngressSettings.ALLOW_ALL,
        "internal-only": functions_v2.ServiceConfig.IngressSettings.ALLOW_INTERNAL_ONLY,
        "internal-and-gclb": functions_v2.ServiceConfig.IngressSettings.ALLOW_INTERNAL_AND_GCLB,
    }
)

# https://cloud.google.com/functions/docs/reference/rest/v2/projects.locations.functions#vpconnectoregresssettings
_VPC_EGRESS_SETTINGS_MAP = types.MappingProxyType(
    {
        "all": functions_v2.ServiceConfig.VpcConnectorEgressSettings.ALL_TRAFFIC,
        "private-ranges-only": functions_v2.ServiceConfig.VpcConnectorEgressSettings.PRIVATE_RANGES_ONLY,
        "unspecified": functions_v2.ServiceConfig.VpcConnectorEgressSettings.VPC_CONNECTOR_EGRESS_SETTINGS_UNSPECIFIED,
    }
)

# BQ managed functions (@udf) currently only support Python 3.11.
_MANAGED_FUNC_PYTHON_VERSION = "python-3.11"

_DEFAULT_FUNCTION_MEMORY_MIB = 1024


class FunctionClient:
    # Wait time (in seconds) for an IAM binding to take effect after creation.
    _iam_wait_seconds = 120

    # TODO(b/392707725): Convert all necessary parameters for cloud function
    # deployment into method parameters.
    def __init__(
        self,
        gcp_project_id,
        bq_location,
        bq_dataset,
        bq_client,
        bq_connection_id,
        bq_connection_manager,
        cloud_function_region=None,
        cloud_functions_client=None,
        cloud_function_service_account=None,
        cloud_function_kms_key_name=None,
        cloud_function_docker_repository=None,
        cloud_build_service_account=None,
        *,
        session: Session,
    ):
        self._gcp_project_id = gcp_project_id
        self._bq_location = bq_location
        self._bq_dataset = bq_dataset
        self._bq_client = bq_client
        self._bq_connection_id = bq_connection_id
        self._bq_connection_manager = bq_connection_manager
        self._session = session

        # Optional attributes only for remote functions.
        self._cloud_function_region = cloud_function_region
        self._cloud_functions_client = cloud_functions_client
        self._cloud_function_service_account = cloud_function_service_account
        self._cloud_function_kms_key_name = cloud_function_kms_key_name
        self._cloud_function_docker_repository = cloud_function_docker_repository
        self._cloud_build_service_account = cloud_build_service_account

    def _create_bq_connection(self) -> None:
        if self._bq_connection_manager:
            self._bq_connection_manager.create_bq_connection(
                self._gcp_project_id,
                self._bq_location,
                self._bq_connection_id,
                "run.invoker",
            )

    def _ensure_dataset_exists(self) -> None:
        # Make sure the dataset exists, i.e. if it doesn't exist, go ahead and
        # create it.
        dataset = bigquery.Dataset(
            bigquery.DatasetReference.from_string(
                self._bq_dataset, default_project=self._gcp_project_id
            )
        )
        dataset.location = self._bq_location
        try:
            # This check does not require bigquery.datasets.create IAM
            # permission. So, if the data set already exists, then user can work
            # without having that permission.
            self._bq_client.get_dataset(dataset)
        except google.api_core.exceptions.NotFound:
            # This requires bigquery.datasets.create IAM permission.
            self._bq_client.create_dataset(dataset, exists_ok=True)

    def _create_bq_function(self, create_function_ddl: str) -> None:
        # TODO(swast): plumb through the original, user-facing api_name.
        import bigframes.session._io.bigquery

        _, query_job = bigframes.session._io.bigquery.start_query_with_client(
            cast(bigquery.Client, self._session.bqclient),
            create_function_ddl,
            job_config=bigquery.QueryJobConfig(),
            location=None,
            project=None,
            timeout=None,
            metrics=None,
            query_with_job=True,
            publisher=self._session._publisher,
        )
        logger.info(f"Created bigframes function {query_job.ddl_target_routine}")

    def _format_function_options(self, function_options: dict) -> str:
        return ", ".join(
            [
                f"{key}='{val}'" if isinstance(val, str) else f"{key}={val}"
                for key, val in function_options.items()
                if val is not None
            ]
        )

    def create_bq_remote_function(
        self,
        input_args: Sequence[str],
        input_types: Sequence[str],
        output_type: str,
        endpoint: str,
        bq_function_name: str,
        max_batching_rows: int,
        metadata: str,
    ):
        """Create a BigQuery remote function given the artifacts of a user defined
        function and the http endpoint of a corresponding cloud function."""
        self._create_bq_connection()

        # Create BQ function
        # https://cloud.google.com/bigquery/docs/reference/standard-sql/remote-functions#create_a_remote_function_2
        bq_function_args = []
        bq_function_return_type = output_type

        # We are expecting the input type annotations to be 1:1 with the input args
        for name, type_ in zip(input_args, input_types):
            bq_function_args.append(f"{name} {type_}")

        remote_function_options = {
            "endpoint": endpoint,
            "max_batching_rows": max_batching_rows,
        }

        if metadata:
            # We are using the description field to store this structured
            # bigframes specific metadata for the lack of a better option
            remote_function_options["description"] = metadata

        remote_function_options_str = self._format_function_options(
            remote_function_options
        )

        create_function_ddl = f"""
            CREATE OR REPLACE FUNCTION `{self._gcp_project_id}.{self._bq_dataset}`.{bq_function_name}({','.join(bq_function_args)})
            RETURNS {bq_function_return_type}
            REMOTE WITH CONNECTION `{self._gcp_project_id}.{self._bq_location}.{self._bq_connection_id}`
            OPTIONS ({remote_function_options_str})"""

        logger.info(f"Creating BQ remote function: {create_function_ddl}")

        self._ensure_dataset_exists()
        self._create_bq_function(create_function_ddl)

    def provision_bq_managed_function(
        self,
        func,
        input_types: Sequence[str],
        output_type: str,
        name: Optional[str],
        packages: Optional[Sequence[str]],
        max_batching_rows: Optional[int],
        container_cpu: Optional[float],
        container_memory: Optional[str],
        is_row_processor: bool,
        bq_connection_id,
        *,
        capture_references: bool = False,
    ):
        """Create a BigQuery managed function."""

        # TODO(b/406283812): Expose the capability to pass down
        # capture_references=True in the public udf API.
        if (
            capture_references
            and (python_version := _utils.get_python_version())
            != _MANAGED_FUNC_PYTHON_VERSION
        ):
            raise bf_formatting.create_exception_with_feedback_link(
                NotImplementedError,
                f"Capturing references for udf is currently supported only in Python version {_MANAGED_FUNC_PYTHON_VERSION}, you are running {python_version}.",
            )

        # Create BQ managed function.
        bq_function_args = []
        bq_function_return_type = output_type

        input_args = inspect.getargs(func.__code__).args
        # We expect the input type annotations to be 1:1 with the input args.
        for name_, type_ in zip(input_args, input_types):
            bq_function_args.append(f"{name_} {type_}")

        managed_function_options: dict[str, Any] = {
            "runtime_version": _MANAGED_FUNC_PYTHON_VERSION,
            "entry_point": "bigframes_handler",
        }
        if max_batching_rows:
            managed_function_options["max_batching_rows"] = max_batching_rows
        if container_cpu:
            managed_function_options["container_cpu"] = container_cpu
        if container_memory:
            managed_function_options["container_memory"] = container_memory

        # Augment user package requirements with any internal package
        # requirements.
        packages = _utils.get_updated_package_requirements(
            packages, is_row_processor, capture_references, ignore_package_version=True
        )
        if packages:
            managed_function_options["packages"] = packages
        managed_function_options_str = self._format_function_options(
            managed_function_options
        )

        session_id = None if name else self._session.session_id
        bq_function_name = name
        if not bq_function_name:
            # Compute a unique hash representing the user code.
            function_hash = _utils.get_hash(func, packages)
            bq_function_name = _utils.get_bigframes_function_name(
                function_hash,
                session_id,
            )

        persistent_func_id = (
            f"`{self._gcp_project_id}.{self._bq_dataset}`.{bq_function_name}"
        )

        udf_name = func.__name__

        with_connection_clause = (
            (
                f"WITH CONNECTION `{self._gcp_project_id}.{self._bq_location}.{self._bq_connection_id}`"
            )
            if bq_connection_id
            else ""
        )

        # Generate the complete Python code block for the managed Python UDF,
        # including the user's function, necessary imports, and the BigQuery
        # handler wrapper.
        python_code_block = bff_template.generate_managed_function_code(
            func, udf_name, is_row_processor, capture_references
        )

        create_function_ddl = (
            textwrap.dedent(
                f"""
                CREATE OR REPLACE FUNCTION {persistent_func_id}({','.join(bq_function_args)})
                RETURNS {bq_function_return_type}
                LANGUAGE python
                {with_connection_clause}
                OPTIONS ({managed_function_options_str})
                AS r'''
                __UDF_PLACE_HOLDER__
                '''
            """
            )
            .strip()
            .replace("__UDF_PLACE_HOLDER__", python_code_block)
        )

        self._ensure_dataset_exists()
        self._create_bq_function(create_function_ddl)

        return bq_function_name

    def get_cloud_function_fully_qualified_parent(self):
        "Get the fully qualilfied parent for a cloud function."
        return self._cloud_functions_client.common_location_path(
            self._gcp_project_id, self._cloud_function_region
        )

    def get_cloud_function_fully_qualified_name(self, name):
        "Get the fully qualilfied name for a cloud function."
        return self._cloud_functions_client.function_path(
            self._gcp_project_id, self._cloud_function_region, name
        )

    def get_remote_function_fully_qualilfied_name(self, name):
        "Get the fully qualilfied name for a BQ remote function."
        return f"{self._gcp_project_id}.{self._bq_dataset}.{name}"

    def get_cloud_function_endpoint(self, name):
        """Get the http endpoint of a cloud function if it exists."""
        fully_qualified_name = self.get_cloud_function_fully_qualified_name(name)
        try:
            response = self._cloud_functions_client.get_function(
                name=fully_qualified_name
            )
            return response.service_config.uri
        except google.api_core.exceptions.NotFound:
            pass
        return None

    def generate_cloud_function_code(
        self,
        def_,
        directory,
        *,
        input_types: Tuple[str],
        output_type: str,
        package_requirements=None,
        is_row_processor=False,
    ):
        """Generate the cloud function code for a given user defined function."""

        # requirements.txt
        if package_requirements:
            requirements_txt = os.path.join(directory, "requirements.txt")
            with open(requirements_txt, "w") as f:
                f.write("\n".join(package_requirements))

        # main.py
        entry_point = bff_template.generate_cloud_function_main_code(
            def_,
            directory,
            input_types=input_types,
            output_type=output_type,
            is_row_processor=is_row_processor,
        )
        return entry_point

    @google.api_core.retry.Retry(
        predicate=google.api_core.retry.if_exception_type(ValueError),
        initial=1.0,
        maximum=10.0,
        multiplier=2.0,
        deadline=300.0,  # Wait up to 5 minutes for propagation
    )
    def _get_cloud_function_endpoint_with_retry(self, name):
        endpoint = self.get_cloud_function_endpoint(name)
        if not endpoint:
            # Raising ValueError triggers the retry predicate
            raise ValueError(f"Endpoint for {name} not yet available.")
        return endpoint

    def create_cloud_function(
        self,
        def_,
        *,
        random_name,
        input_types: Tuple[str],
        output_type: str,
        package_requirements=None,
        timeout_seconds=600,
        max_instance_count=None,
        is_row_processor=False,
        vpc_connector=None,
        vpc_connector_egress_settings="private-ranges-only",
        memory_mib=None,
        cpus=None,
        ingress_settings="internal-only",
        workers=None,
        threads=None,
        concurrency=None,
    ):
        """Create a cloud function from the given user defined function."""

        # Build and deploy folder structure containing cloud function
        with tempfile.TemporaryDirectory() as directory:
            entry_point = self.generate_cloud_function_code(
                def_,
                directory,
                package_requirements=package_requirements,
                input_types=input_types,
                output_type=output_type,
                is_row_processor=is_row_processor,
            )
            archive_path = shutil.make_archive(directory, "zip", directory)

            # We are creating cloud function source code from the currently running
            # python version. Use the same version to deploy. This is necessary
            # because cloudpickle serialization done in one python version and
            # deserialization done in another python version doesn't work.
            # TODO(shobs): Figure out how to achieve version compatibility, specially
            # when pickle (internally used by cloudpickle) guarantees that:
            # https://docs.python.org/3/library/pickle.html#:~:text=The%20pickle%20serialization%20format%20is,unique%20breaking%20change%20language%20boundary.
            python_version = _utils.get_python_version(is_compat=True)

            # Determine an upload URL for user code
            upload_url_request = functions_v2.GenerateUploadUrlRequest(
                kms_key_name=self._cloud_function_kms_key_name
            )
            upload_url_request.parent = self.get_cloud_function_fully_qualified_parent()
            upload_url_response = self._cloud_functions_client.generate_upload_url(
                request=upload_url_request
            )

            # Upload the code to GCS
            with open(archive_path, "rb") as f:
                response = requests.put(
                    upload_url_response.upload_url,
                    data=f,
                    headers={"content-type": "application/zip"},
                )
                if response.status_code != 200:
                    raise bf_formatting.create_exception_with_feedback_link(
                        RuntimeError,
                        f"Failed to upload user code. code={response.status_code}, reason={response.reason}, text={response.text}",
                    )

            # Deploy Cloud Function
            create_function_request = functions_v2.CreateFunctionRequest()
            create_function_request.parent = (
                self.get_cloud_function_fully_qualified_parent()
            )
            create_function_request.function_id = random_name
            function = functions_v2.Function()
            function.name = self.get_cloud_function_fully_qualified_name(random_name)
            function.build_config = functions_v2.BuildConfig()
            function.build_config.runtime = python_version
            function.build_config.entry_point = entry_point
            function.build_config.source = functions_v2.Source()
            function.build_config.source.storage_source = functions_v2.StorageSource()
            function.build_config.source.storage_source.bucket = (
                upload_url_response.storage_source.bucket
            )
            function.build_config.source.storage_source.object_ = (
                upload_url_response.storage_source.object_
            )
            function.build_config.docker_repository = (
                self._cloud_function_docker_repository
            )

            if self._cloud_build_service_account:
                canonical_cloud_build_service_account = (
                    self._cloud_build_service_account
                    if "/" in self._cloud_build_service_account
                    else f"projects/{self._gcp_project_id}/serviceAccounts/{self._cloud_build_service_account}"
                )
                function.build_config.service_account = (
                    canonical_cloud_build_service_account
                )

            function.service_config = functions_v2.ServiceConfig()
            if memory_mib is not None:
                function.service_config.available_memory = f"{memory_mib}Mi"
            if cpus is not None:
                function.service_config.available_cpu = str(cpus)
            if timeout_seconds is not None:
                if timeout_seconds > 1200:
                    raise bf_formatting.create_exception_with_feedback_link(
                        ValueError,
                        "BigQuery remote function can wait only up to 20 minutes"
                        ", see for more details "
                        "https://cloud.google.com/bigquery/quotas#remote_function_limits.",
                    )
                function.service_config.timeout_seconds = timeout_seconds
            if max_instance_count is not None:
                function.service_config.max_instance_count = max_instance_count
            if vpc_connector is not None:
                function.service_config.vpc_connector = vpc_connector
                if vpc_connector_egress_settings is None:
                    msg = bfe.format_message(
                        "The 'vpc_connector_egress_settings' was not specified. Defaulting to 'private-ranges-only'.",
                    )
                    warnings.warn(msg, category=UserWarning)
                    vpc_connector_egress_settings = "private-ranges-only"
                if vpc_connector_egress_settings not in _VPC_EGRESS_SETTINGS_MAP:
                    raise bf_formatting.create_exception_with_feedback_link(
                        ValueError,
                        f"'{vpc_connector_egress_settings}' is not one of the supported vpc egress settings values: {list(_VPC_EGRESS_SETTINGS_MAP)}",
                    )
                function.service_config.vpc_connector_egress_settings = cast(
                    functions_v2.ServiceConfig.VpcConnectorEgressSettings,
                    _VPC_EGRESS_SETTINGS_MAP[vpc_connector_egress_settings],
                )
            function.service_config.service_account_email = (
                self._cloud_function_service_account
            )
            if concurrency:
                function.service_config.max_instance_request_concurrency = concurrency

            # Functions framework use environment variables to pass config to gunicorn
            # See https://github.com/GoogleCloudPlatform/functions-framework-python/issues/241
            # Code: https://github.com/GoogleCloudPlatform/functions-framework-python/blob/v3.10.1/src/functions_framework/_http/gunicorn.py#L37-L43
            env_vars = {}
            if workers:
                env_vars["WORKERS"] = str(workers)
            if threads:
                env_vars["THREADS"] = str(threads)
            if env_vars:
                function.service_config.environment_variables = env_vars

            if ingress_settings not in _INGRESS_SETTINGS_MAP:
                raise bf_formatting.create_exception_with_feedback_link(
                    ValueError,
                    f"'{ingress_settings}' not one of the supported ingress settings values: {list(_INGRESS_SETTINGS_MAP)}",
                )
            function.service_config.ingress_settings = cast(
                functions_v2.ServiceConfig.IngressSettings,
                _INGRESS_SETTINGS_MAP[ingress_settings],
            )
            function.kms_key_name = self._cloud_function_kms_key_name
            create_function_request.function = function

            # Create the cloud function and wait for it to be ready to use
            endpoint = None
            try:
                operation = self._cloud_functions_client.create_function(
                    request=create_function_request
                )
                # operation.result() returns the Function object upon completion
                function_obj = operation.result()
                endpoint = function_obj.service_config.uri

                # Cleanup
                os.remove(archive_path)
            except google.api_core.exceptions.AlreadyExists:
                # b/437124912: The most likely scenario is that
                # `create_function` had a retry due to a network issue. The
                # retried request then fails because the first call actually
                # succeeded, but we didn't get the successful response back.
                #
                # Since the function name was randomly chosen to avoid
                # conflicts, we know the AlreadyExist can only happen because
                # we created it. This error is safe to ignore.
                pass

        # Fetch the endpoint with retries if it wasn't returned by the operation
        if not endpoint:
            try:
                endpoint = self._get_cloud_function_endpoint_with_retry(random_name)
            except Exception as e:
                raise bf_formatting.create_exception_with_feedback_link(
                    ValueError, f"Couldn't fetch the http endpoint: {e}"
                )

        logger.info(
            f"Successfully created cloud function {random_name} with uri ({endpoint})"
        )
        return endpoint

    def provision_bq_remote_function(
        self,
        def_,
        input_types,
        output_type,
        reuse,
        name,
        package_requirements,
        max_batching_rows,
        cloud_function_timeout,
        cloud_function_max_instance_count,
        is_row_processor,
        cloud_function_vpc_connector,
        cloud_function_vpc_connector_egress_settings,
        cloud_function_memory_mib,
        cloud_function_cpus,
        cloud_function_ingress_settings,
        bq_metadata,
    ):
        """Provision a BigQuery remote function."""
        # Augment user package requirements with any internal package
        # requirements
        package_requirements = _utils.get_updated_package_requirements(
            package_requirements, is_row_processor
        )

        # Compute a unique hash representing the user code
        function_hash = _utils.get_hash(def_, package_requirements)

        # If reuse of any existing function with the same name (indicated by the
        # same hash of its source code) is not intended, then attach a unique
        # suffix to the intended function name to make it unique.
        uniq_suffix = None
        if not reuse:
            # use 4 digits as a unique suffix which should suffice for
            # uniqueness per session
            uniq_suffix = "".join(
                random.choices(string.ascii_lowercase + string.digits, k=4)
            )

        # Derive the name of the cloud function underlying the intended BQ
        # remote function. Use the session id to identify the GCF for unnamed
        # functions. The named remote functions are treated as a persistant
        # artifacts, so let's keep them independent of session id, which also
        # makes their naming more stable for the same udf code
        session_id = None if name else self._session.session_id
        cloud_function_name = _utils.get_cloud_function_name(
            function_hash, session_id, uniq_suffix
        )
        cf_endpoint = self.get_cloud_function_endpoint(cloud_function_name)

        if cloud_function_memory_mib is None:
            cloud_function_memory_mib = _DEFAULT_FUNCTION_MEMORY_MIB

        # assumption is most bigframes functions are cpu bound, single-threaded and many won't release GIL
        # therefore, want to allocate a worker for each cpu, and allow a concurrent request per worker
        expected_cpus = cloud_function_cpus or _infer_cpus_from_memory(
            cloud_function_memory_mib
        )
        workers = expected_cpus
        threads = 4  # (per worker)
        concurrency = workers * threads

        # Create the cloud function if it does not exist
        if not cf_endpoint:
            cf_endpoint = self.create_cloud_function(
                def_,
                random_name=cloud_function_name,
                input_types=input_types,
                output_type=output_type,
                package_requirements=package_requirements,
                timeout_seconds=cloud_function_timeout,
                max_instance_count=cloud_function_max_instance_count,
                is_row_processor=is_row_processor,
                vpc_connector=cloud_function_vpc_connector,
                vpc_connector_egress_settings=cloud_function_vpc_connector_egress_settings,
                memory_mib=cloud_function_memory_mib,
                cpus=cloud_function_cpus,
                ingress_settings=cloud_function_ingress_settings,
                workers=workers,
                threads=threads,
                concurrency=concurrency,
            )
        else:
            logger.info(f"Cloud function {cloud_function_name} already exists.")

        # Derive the name of the remote function
        remote_function_name = name
        if not remote_function_name:
            remote_function_name = _utils.get_bigframes_function_name(
                function_hash, self._session.session_id, uniq_suffix
            )
        rf_endpoint, rf_conn = self.get_remote_function_specs(remote_function_name)

        # Create the BQ remote function in following circumstances:
        # 1. It does not exist
        # 2. It exists but the existing remote function has different
        #    configuration than intended
        created_new = False
        if not rf_endpoint or (
            rf_endpoint != cf_endpoint or rf_conn != self._bq_connection_id
        ):
            input_args = inspect.getargs(def_.__code__).args
            if len(input_args) != len(input_types):
                raise bf_formatting.create_exception_with_feedback_link(
                    ValueError,
                    "Exactly one type should be provided for every input arg.",
                )
            self.create_bq_remote_function(
                input_args,
                input_types,
                output_type,
                cf_endpoint,
                remote_function_name,
                max_batching_rows,
                bq_metadata,
            )

            created_new = True
        else:
            logger.info(f"Remote function {remote_function_name} already exists.")

        return remote_function_name, cloud_function_name, created_new

    def get_remote_function_specs(self, remote_function_name):
        """Check whether a remote function already exists for the udf."""
        http_endpoint = None
        bq_connection = None
        routines = self._bq_client.list_routines(
            f"{self._gcp_project_id}.{self._bq_dataset}"
        )
        try:
            for routine in routines:
                routine = cast(bigquery.Routine, routine)
                if routine.reference.routine_id == remote_function_name:
                    rf_options = routine.remote_function_options
                    if rf_options:
                        http_endpoint = rf_options.endpoint
                        bq_connection = rf_options.connection
                        if bq_connection:
                            bq_connection = os.path.basename(bq_connection)
                    break
        except google.api_core.exceptions.NotFound:
            # The dataset might not exist, in which case the http_endpoint doesn't, either.
            # Note: list_routines doesn't make an API request until we iterate on the response object.
            pass
        return (http_endpoint, bq_connection)


def _infer_cpus_from_memory(memory_mib: int) -> int:
    # observed values, not formally documented by cloud run functions
    if memory_mib <= 2048:
        # in actuality, will be 0.583 for 1024mb, 0.33 for 512mb, etc, but we round up to 1
        return 1
    elif memory_mib <= 8192:
        return 2
    elif memory_mib <= 16384:
        return 4
    elif memory_mib <= 32768:
        return 8
    else:
        raise ValueError("Cloud run supports at most 32768MiB per instance")