The spark integration brings two different step operators:
  • Step Operator: The SparkStepOperator serves as the base class for all the Spark-related step operators.
  • Step Operator: The KubernetesSparkStepOperator is responsible for launching ZenML steps as Spark applications with Kubernetes as a cluster manager.

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Step Operators: SparkStepOperator

A summarized version of the implementation can be summarized in two parts. First, the configuration: 
from typing import Optional, Dict, Any
from zenml.step_operators import BaseStepOperatorConfig

class SparkStepOperatorConfig(BaseStepOperatorConfig):
    """Spark step operator config.

    Attributes:
        master: is the master URL for the cluster. You might see different
            schemes for different cluster managers which are supported by Spark
            like Mesos, YARN, or Kubernetes. Within the context of this PR,
            the implementation supports Kubernetes as a cluster manager.
        deploy_mode: can either be 'cluster' (default) or 'client' and it
            decides where the driver node of the application will run.
        submit_kwargs: is the JSON string of a dict, which will be used
            to define additional params if required (Spark has quite a
            lot of different parameters, so including them, all in the step
            operator was not implemented).
    """

    master: str
    deploy_mode: str = "cluster"
    submit_kwargs: Optional[Dict[str, Any]] = None
and then the implementation: 
from typing import List
from pyspark.conf import SparkConf

from zenml.step_operators import BaseStepOperator

class SparkStepOperator(BaseStepOperator):
    """Base class for all Spark-related step operators."""

    def _resource_configuration(
        self,
        spark_config: SparkConf,
        resource_configuration: "ResourceSettings",
    ) -> None:
      """Configures Spark to handle the resource configuration."""

    def _backend_configuration(
        self,
        spark_config: SparkConf,
        step_config: "StepConfiguration",
    ) -> None:
        """Configures Spark to handle backends like YARN, Mesos or Kubernetes."""

    def _io_configuration(
        self, 
        spark_config: SparkConf
    ) -> None:
        """Configures Spark to handle different input/output sources."""

    def _additional_configuration(
        self, 
        spark_config: SparkConf
	) -> None:
        """Appends the user-defined configuration parameters."""

    def _launch_spark_job(
        self, 
        spark_config: SparkConf, 
        entrypoint_command: List[str]
    ) -> None:
        """Generates and executes a spark-submit command."""

    def launch(
        self,
        info: "StepRunInfo",
        entrypoint_command: List[str],
    ) -> None:
        """Launches the step on Spark."""
Under the base configuration, you will see is the main configuration parameters:
  • master is the master URL for the cluster where Spark will run. You might see different schemes for this URL with varying cluster managers such as Mesos, YARN, or Kubernetes.
  • deploy_mode can either be ‘cluster’ (default) or ‘client’ and it decides where the driver node of the application will run.
  • submit_args is the JSON string of a dictionary, which will be used to define additional params if required (Spark has a wide variety of parameters, thus including them all in a single class was deemed unnecessary.).
In addition to this configuration, the launch method of the step operator gets additional configuration parameters from the DockerSettings and ResourceSettings. As a result, the overall configuration happens in 4 base methods:
  • _resource_configuration translates the ZenML ResourceSettings object to Spark’s own resource configuration.
  • _backend_configuration is responsible for cluster-manager-specific configuration.
  • _io_configuration is a critical method. Even though we have materializers, Spark might require additional packages and configuration to work with a specific filesystem. This method is used as an interface to provide this configuration.
  • _additional_configuration takes the submit_args, converts, and appends them to the overall configuration.
Once the configuration is completed, _launch_spark_job comes into play. This takes the completed configuration and runs a Spark job on the given master URL with the specified deploy_mode. By default, this is achieved by creating and executing a spark-submit command.

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Warning

In its first iteration, the pre-configuration with _io_configuration method is only effective when it is paired with an S3ArtifactStore (which has an authentication secret). When used with other artifact store flavors, you might be required to provide additional configuration through the submit_args.

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Stack Component: KubernetesSparkStepOperator

The KubernetesSparkStepOperator is implemented by subclassing the base SparkStepOperator and uses the PipelineDockerImageBuilder class to build and push the required docker images. 
from typing import Optional

from zenml.integrations.spark.step_operators.spark_step_operator import (
    SparkStepOperatorConfig
)

class KubernetesSparkStepOperatorConfig(SparkStepOperatorConfig):
    """Config for the Kubernetes Spark step operator."""

    namespace: Optional[str] = None
    service_account: Optional[str] = None

from typing import Optional
from pyspark.conf import SparkConf

from zenml.utils.pipeline_docker_image_builder import PipelineDockerImageBuilder
from zenml.integrations.spark.step_operators.spark_step_operator import (
    SparkStepOperator
)

class KubernetesSparkStepOperator(SparkStepOperator):
    """Step operator which runs Steps with Spark on Kubernetes."""

    def _backend_configuration(
        self,
        spark_config: SparkConf,
        step_config: "StepConfiguration",
    ) -> None:
        """Configures Spark to run on Kubernetes."""
        # Build and push the image
        docker_image_builder = PipelineDockerImageBuilder()
        image_name = docker_image_builder.build_and_push_docker_image(...)

        # Adjust the spark configuration
        spark_config.set("spark.kubernetes.container.image", image_name)
        ...
For Kubernetes, there are also some additional important configuration parameters:
  • namespace is the namespace under which the driver and executor pods will run.
  • service_account is the service account that will be used by various Spark components (to create and watch the pods).
Additionally, the _backend_configuration method is adjusted to handle the Kubernetes-specific configuration.

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When to use it

You should use the Spark step operator:
  • when you are dealing with large amounts of data.
  • when you are designing a step which can benefit from distributed computing paradigms in terms of time and resources.

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How to deploy it

The KubernetesSparkStepOperator requires a Kubernetes cluster in order to run. There are many ways to deploy a Kubernetes cluster using different cloud providers or on your custom infrastructure, and we can’t possibly cover all of them, but you can check out the spark example to see how it is deployed on AWS.

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How to use it

In order to use the KubernetesSparkStepOperator, you need:
  • the ZenML spark integration. If you haven’t installed it already, run
zenml integration install spark
We can then register the step operator and use it in our active stack: 
zenml step-operator register  \
	--flavor=spark-kubernetes \
	--master=k8s:// \
	--namespace= \
	--service_account=
Once you added the step operator to your active stack, you can use it to execute individual steps of your pipeline by specifying it in the @step decorator as follows: 
from zenml.steps import step

@step(step_operator=)
def preprocess(...) -> ...:
    """Preprocess your dataset."""
    # This step will be executed with Spark on Kubernetes.

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Additional configuration

For additional configuration of the Spark step operator, you can pass SparkStepOperatorSettings when defining or running your pipeline. Check out the API docs for a full list of available attributes and this docs page for more information on how to specify settings. A concrete example of using the Spark step operator can be found here.