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How to use Apache Spark (powered by Azure Synapse Analytics) in your machine learning pipeline (deprecated)

  • Raksts

APPLIES TO: Python SDK azureml v1

Warning

The Azure Synapse Analytics integration with Azure Machine Learning, available in Python SDK v1, is deprecated. Users can still use Synapse workspace, registered with Azure Machine Learning, as a linked service. However, a new Synapse workspace can no longer be registered with Azure Machine Learning as a linked service. We recommend use of serverless Spark compute and attached Synapse Spark pools, available in CLI v2 and Python SDK v2. For more information, visit https://aka.ms/aml-spark.

In this article, you learn how to use Apache Spark pools powered by Azure Synapse Analytics as the compute target for a data preparation step in an Azure Machine Learning pipeline. You learn how a single pipeline can use compute resources suited for the specific step - for example, data preparation or training. You'll also learn how data is prepared for the Spark step and how it passes to the next step.

Prerequisites

You create and administer your Apache Spark pools in an Azure Synapse Analytics workspace. To integrate an Apache Spark pool with an Azure Machine Learning workspace, you must link to the Azure Synapse Analytics workspace. Once you link your Azure Machine Learning workspace and your Azure Synapse Analytics workspaces, you can attach an Apache Spark pool with

  • Azure Machine Learning studio

  • Python SDK, as explained later

  • Azure Resource Manager (ARM) template. For more information, visit Example ARM template

    • You can use the command line to follow the ARM template, add the linked service, and attach the Apache Spark pool with this code sample:
    az deployment group create --name --resource-group <rg_name> --template-file "azuredeploy.json" --parameters @"azuredeploy.parameters.json"

Important

To successfully link to the Synapse workspace, you must be granted the Owner role of the Synapse workspace. Check your access in the Azure portal.

The linked service will get a system-assigned managed identity (SAI) at creation time. You must assign this link service SAI the "Synapse Apache Spark administrator" role from Synapse Studio, so that it can submit the Spark job (see How to manage Synapse RBAC role assignments in Synapse Studio).

You must also give the user of the Azure Machine Learning workspace the "Contributor" role, from Azure portal of resource management.

This code shows how to retrieve linked services in your workspace:

from azureml.core import Workspace, LinkedService, SynapseWorkspaceLinkedServiceConfiguration

ws = Workspace.from_config()

for service in LinkedService.list(ws) : 
    print(f"Service: {service}")

# Retrieve a known linked service
linked_service = LinkedService.get(ws, 'synapselink1')

First, Workspace.from_config() accesses your Azure Machine Learning workspace with the configuration in the config.json file. (For more information, visit Create a workspace configuration file). Then, the code prints all of the linked services available in the workspace. Finally, LinkedService.get() retrieves a linked service named 'synapselink1'.

Attach your Apache spark pool as a compute target for Azure Machine Learning

To use your Apache spark pool to power a step in your machine learning pipeline, you must attach it as a ComputeTarget for the pipeline step, as shown in this code sample:

from azureml.core.compute import SynapseCompute, ComputeTarget

attach_config = SynapseCompute.attach_configuration(
        linked_service = linked_service,
        type="SynapseSpark",
        pool_name="spark01") # This name comes from your Synapse workspace

synapse_compute=ComputeTarget.attach(
        workspace=ws,
        name='link1-spark01',
        attach_configuration=attach_config)

synapse_compute.wait_for_completion()

The code first configures the SynapseCompute. The linked_service argument is the LinkedService object you created or retrieved in the previous step. The type argument must be SynapseSpark. The pool_name argument in SynapseCompute.attach_configuration() must match that of an existing pool in your Azure Synapse Analytics workspace. For more information about creation of an Apache spark pool in the Azure Synapse Analytics workspace, visit Quickstart: Create a serverless Apache Spark pool using Synapse Studio. The attach_config type is ComputeTargetAttachConfiguration.

After creation of the configuration, create a machine learning ComputeTarget by passing in the Workspace and ComputeTargetAttachConfiguration values, and the name by which you'd like to refer to the compute within the machine learning workspace. The call to ComputeTarget.attach() is asynchronous, so the sample is blocked until the call completes.

Create a SynapseSparkStep that uses the linked Apache Spark pool

The sample notebook Spark job on Apache spark pool defines a simple machine learning pipeline. First, the notebook defines a data preparation step, powered by the synapse_compute defined in the previous step. Then, the notebook defines a training step powered by a compute target more appropriate for training. The sample notebook uses the Titanic survival database to show data input and output. It doesn't actually clean the data or make a predictive model. Since this sample doesn't really involve training, the training step uses an inexpensive, CPU-based compute resource.

Data flows into a machine learning pipeline through DatasetConsumptionConfig objects, which can hold tabular data or sets of files. The data often comes from files in blob storage in a workspace datastore. This code sample shows typical code that creates input for a machine learning pipeline:

from azureml.core import Dataset

datastore = ws.get_default_datastore()
file_name = 'Titanic.csv'

titanic_tabular_dataset = Dataset.Tabular.from_delimited_files(path=[(datastore, file_name)])
step1_input1 = titanic_tabular_dataset.as_named_input("tabular_input")

# Example only: it wouldn't make sense to duplicate input data, especially one as tabular and the other as files
titanic_file_dataset = Dataset.File.from_files(path=[(datastore, file_name)])
step1_input2 = titanic_file_dataset.as_named_input("file_input").as_hdfs()

The code sample assumes that the file Titanic.csv is in blob storage. The code shows how to read the file both as a TabularDataset and as a FileDataset. This code is for demonstration purposes only, because it would become confusing to duplicate inputs or to interpret a single data source as both a table-containing resource, and strictly as a file.

Important

To use a FileDataset as input, you need an azureml-core version of at least 1.20.0. You can specify this with the Environment class, as discussed later. When a step completes, you can store the output data, as shown in this code sample:

from azureml.data import HDFSOutputDatasetConfig
step1_output = HDFSOutputDatasetConfig(destination=(datastore,"test")).register_on_complete(name="registered_dataset")

In this code sample, the datastore would store the data in a file named test. The data would be available within the machine learning workspace as a Dataset, with the name registered_dataset.

In addition to data, a pipeline step can have per-step Python dependencies. Additionally, individual SynapseSparkStep objects can specify their precise Azure Synapse Apache Spark configuration. To show this, the following code sample specifies that the azureml-core package version must be at least 1.20.0. As mentioned previously, this requirement for the azureml-core package is needed to use a FileDataset as an input.

from azureml.core.environment import Environment
from azureml.pipeline.steps import SynapseSparkStep

env = Environment(name="myenv")
env.python.conda_dependencies.add_pip_package("azureml-core>=1.20.0")

step_1 = SynapseSparkStep(name = 'synapse-spark',
                          file = 'dataprep.py',
                          source_directory="./code", 
                          inputs=[step1_input1, step1_input2],
                          outputs=[step1_output],
                          arguments = ["--tabular_input", step1_input1, 
                                       "--file_input", step1_input2,
                                       "--output_dir", step1_output],
                          compute_target = 'link1-spark01',
                          driver_memory = "7g",
                          driver_cores = 4,
                          executor_memory = "7g",
                          executor_cores = 2,
                          num_executors = 1,
                          environment = env)

This code specifies a single step in the Azure Machine Learning pipeline. The environment value of this code sets a specific azureml-core version, and the code can add other conda or pip dependencies as needed.

The SynapseSparkStep zips and uploads the ./code subdirectory from the local computer. That directory is recreated on the compute server, and the step runs the dataprep.py script from that directory. The inputs and outputs of that step are the step1_input1, step1_input2, and step1_output objects discussed earlier. The easiest way to access those values within the dataprep.py script is to associate them with named arguments.

The next set of arguments to the SynapseSparkStep constructor controls Apache Spark. The compute_target is the 'link1-spark01' that we attached as a compute target previously. The other parameters specify the memory and cores we'd like to use.

The sample notebook uses this code for dataprep.py:

import os
import sys
import azureml.core
from pyspark.sql import SparkSession
from azureml.core import Run, Dataset

print(azureml.core.VERSION)
print(os.environ)

import argparse
parser = argparse.ArgumentParser()
parser.add_argument("--tabular_input")
parser.add_argument("--file_input")
parser.add_argument("--output_dir")
args = parser.parse_args()

# use dataset sdk to read tabular dataset
run_context = Run.get_context()
dataset = Dataset.get_by_id(run_context.experiment.workspace,id=args.tabular_input)
sdf = dataset.to_spark_dataframe()
sdf.show()

# use hdfs path to read file dataset
spark= SparkSession.builder.getOrCreate()
sdf = spark.read.option("header", "true").csv(args.file_input)
sdf.show()

sdf.coalesce(1).write\
.option("header", "true")\
.mode("append")\
.csv(args.output_dir)

This "data preparation" script doesn't do any real data transformation, but it shows how to retrieve data, convert it to a Spark dataframe, and how to do some basic Apache Spark manipulation. To find the output in Azure Machine Learning studio, open the child job, choose the Outputs + logs tab, and open the logs/azureml/driver/stdout file, as shown in this screenshot:

Screenshot of Studio showing stdout tab of child job

Use the SynapseSparkStep in a pipeline

The next example uses the output from the SynapseSparkStep created in the previous section. Other steps in the pipeline might have their own unique environments, and might run on different compute resources appropriate to the task at hand. The sample notebook runs the "training step" on a small CPU cluster:

from azureml.core.compute import AmlCompute

cpu_cluster_name = "cpucluster"

if cpu_cluster_name in ws.compute_targets:
    cpu_cluster = ComputeTarget(workspace=ws, name=cpu_cluster_name)
    print('Found existing cluster, use it.')
else:
    compute_config = AmlCompute.provisioning_configuration(vm_size='STANDARD_D2_V2', max_nodes=1)
    cpu_cluster = ComputeTarget.create(ws, cpu_cluster_name, compute_config)
    print('Allocating new CPU compute cluster')

cpu_cluster.wait_for_completion(show_output=True)

step2_input = step1_output.as_input("step2_input").as_download()

step_2 = PythonScriptStep(script_name="train.py",
                          arguments=[step2_input],
                          inputs=[step2_input],
                          compute_target=cpu_cluster_name,
                          source_directory="./code",
                          allow_reuse=False)

This code creates the new compute resource if necessary. Then, it converts the step1_output result to input for the training step. The as_download() option means that the data is moved onto the compute resource, resulting in faster access. If the data was so large that it wouldn't fit on the local compute hard drive, you must use the as_mount() option to stream the data with the FUSE filesystem. The compute_target of this second step is 'cpucluster', not the 'link1-spark01' resource you used in the data preparation step. This step uses a simple train.py script instead of the dataprep.py script you used in the previous step. The sample notebook has details of the train.py script.

After you define all of your steps, you can create and run your pipeline.

from azureml.pipeline.core import Pipeline

pipeline = Pipeline(workspace=ws, steps=[step_1, step_2])
pipeline_run = pipeline.submit('synapse-pipeline', regenerate_outputs=True)

This code creates a pipeline consisting of the data preparation step on Apache Spark pools, powered by Azure Synapse Analytics (step_1) and the training step (step_2). Azure examines the data dependencies between the steps to calculate the execution graph. In this case, there's only one straightforward dependency. Here, step2_input necessarily requires step1_output.

The pipeline.submit call creates, if necessary, an Experiment named synapse-pipeline, and asynchronously starts a Job within it. Individual steps within the pipeline run as Child Jobs of this main job, and the Experiments page of Studio can monitor and review those steps.

Next steps