To deploy and manage your trained machine learning models, ZenML provides a stack component called Model Deployer. This component is responsible for interacting with the deployment tool, framework or platform.

When present in a stack, the model deployer can also act as a registry for models that are served with ZenML. You can use the model deployer to list all models that are currently deployed for online inference or filtered according to a particular pipeline run or step, or to suspend, resume or delete an external model server managed through ZenML.

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Base Abstraction

In ZenML, the base abstraction of the model deployer is built on top of three major criteria:

  1. It needs to contain all the stack-related configuration attributes required to interact with the remote model serving tool, service or platform (e.g. hostnames, URLs, references to credentials, other client-related configuration parameters).

  2. It needs to implement the continuous deployment logic necessary to deploy models in a way that updates an existing model server that is already serving a previous version of the same model instead of creating a new model server for every new model version (see the deploy_model abstract method). This functionality can be consumed directly from ZenML pipeline steps, but it can also be used outside the pipeline to deploy ad-hoc models. It is also usually coupled with a standard model deployer step, implemented by each integration, that hides the details of the deployment process from the user.

  3. It needs to act as a ZenML BaseService registry, where every BaseService instance is used as an internal representation of a remote model server (see the find_model_server abstract method). To achieve this, it must be able to re-create the configuration of a BaseService from information that is persisted externally, alongside or even as part of the remote model server configuration itself. For example, for model servers that are implemented as Kubernetes resources, the BaseService instances can be serialized and saved as Kubernetes resource annotations. This allows the model deployer to keep track of all externally running model servers and to re-create their corresponding BaseService instance representations at any given time. The model deployer also defines methods that implement basic life-cycle management on remote model servers outside the coverage of a pipeline (see stop_model_server, start_model_server and delete_model_server).

Putting all these considerations together, we end up with the following interface:

from abc import ABC, abstractmethod
from typing import Dict, List, Optional, Type
from uuid import UUID

from zenml.enums import StackComponentType
from zenml.services import BaseService, ServiceConfig
from zenml.stack import StackComponent, StackComponentConfig, Flavor

DEFAULT_DEPLOYMENT_START_STOP_TIMEOUT = 300

class BaseModelDeployerConfig(StackComponentConfig):
    """Base class for all ZenML model deployer configurations."""

class BaseModelDeployer(StackComponent, ABC):
    """Base class for all ZenML model deployers."""

    @abstractmethod
    def deploy_model(
        self,
        config: ServiceConfig,
        replace: bool = False,
        timeout: int = DEFAULT_DEPLOYMENT_START_STOP_TIMEOUT,
    ) -> BaseService:
        """Abstract method to deploy a model."""

    @staticmethod
    @abstractmethod
    def get_model_server_info(
        service: BaseService,
    ) -> Dict[str, Optional[str]]:
        """Give implementation-specific way to extract relevant model server
        properties for the user."""

    @abstractmethod
    def find_model_server(
        self,
        running: bool = False,
        service_uuid: Optional[UUID] = None,
        pipeline_name: Optional[str] = None,
        pipeline_run_id: Optional[str] = None,
        pipeline_step_name: Optional[str] = None,
        model_name: Optional[str] = None,
        model_uri: Optional[str] = None,
        model_type: Optional[str] = None,
    ) -> List[BaseService]:
        """Abstract method to find one or more model servers that match the
        given criteria."""

    @abstractmethod
    def stop_model_server(
        self,
        uuid: UUID,
        timeout: int = DEFAULT_DEPLOYMENT_START_STOP_TIMEOUT,
        force: bool = False,
    ) -> None:
        """Abstract method to stop a model server."""

    @abstractmethod
    def start_model_server(
        self,
        uuid: UUID,
        timeout: int = DEFAULT_DEPLOYMENT_START_STOP_TIMEOUT,
    ) -> None:
        """Abstract method to start a model server."""

    @abstractmethod
    def delete_model_server(
        self,
        uuid: UUID,
        timeout: int = DEFAULT_DEPLOYMENT_START_STOP_TIMEOUT,
        force: bool = False,
    ) -> None:
        """Abstract method to delete a model server."""


class BaseModelDeployerFlavor(Flavor):
    """Base class for model deployer flavors."""

    @property
    @abstractmethod
    def name(self):
        """Returns the name of the flavor."""

    @property
    def type(self) -> StackComponentType:
        """Returns the flavor type.

        Returns:
            The flavor type.
        """
        return StackComponentType.MODEL_DEPLOYER

    @property
    def config_class(self) -> Type[BaseModelDeployerConfig]:
        """Returns `BaseModelDeployerConfig` config class.

        Returns:
                The config class.
        """
        return BaseModelDeployerConfig

    @property
    @abstractmethod
    def implementation_class(self) -> Type[BaseModelDeployer]:
        """The class that implements the model deployer."""

This is a slimmed-down version of the base implementation which aims to highlight the abstraction layer. In order to see the full implementation and get the complete docstrings, please check the API docs.

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Building your own model deployers

If you want to create your own custom flavor for a model deployer, you can follow the following steps:

  1. Create a class which inherits from the BaseModelDeployer class and implement the abstract methods.
  2. If you need to provide any configuration, create a class which inherits from the BaseModelDeployerConfig class add your configuration parameters.
  3. Bring both of the implementation and the configuration together by inheriting from the BaseModelDeployerFlavor class. Make sure that you give a name to the flavor through its abstract property.

Once you are done with the implementation, you can register it through the CLI as:

zenml model-deployer flavor register

It is important to draw attention to when and how these base abstractions are coming into play in a ZenML workflow.

  • The CustomModelDeployerFlavor class is imported and utilized upon the creation of the custom flavor through the CLI.
  • The CustomModelDeployerConfig class is imported when someone tries to register/update a stack component with this custom flavor. Especially, during the registration process of the stack component, the config will be used to validate the values given by the user. As Config object are inherently pydantic objects, you can also add your own custom validators here.
  • The CustomModelDeployer only comes into play when the component is ultimately in use.

The design behind this interaction lets us separate the configuration of the flavor from its implementation. This way we can register flavors and components even when the major dependencies behind their implementation are not installed in our local setting (assuming the CustomModelDeployerFlavor and the CustomModelDeployerConfig are implemented in a different module/path than the actual CustomModelDeployer).