This article provides details around how ModelOp Center leverages spark-submit to orchestrate the submission and management of Spark jobs within Spark environments.

Table of Contents

1 Overview
2 Architecture Overview
3 Details
- 3.1 PySpark Dynamic Job Abstraction
- 3.2 PySparkJobManifest
- 3.3 ModelOpJobMonitor
- 3.4 PySpark Job Input and Output Data
  - 3.4.1 Input Data by URL
  - 3.4.2 Input Data Embedded
  - 3.4.3 Output Data by URL
  - 3.4.4 Output Data Embedded
- 3.5 PySpark - Metrics Jobs

Overview

The spark-submit execution process was designed and architected with the following principles and features in mind:

When possible, Python and/or PySpark components should be implemented in python. This principle will ensure testing and debugging are easier when running in local or cluster deploy mode
The spark-runtime-service is monitoring jobs in WAITING and RUNNING state until they reach their COMPLETE, ERROR or CANCELLED state. If any new job changes are detected, model manager will be updated accordingly
Before a job is submitted to the Spark cluster for execution, the ModelOpPySparkDriver implementation will extract the inputData, outputData and storedModel.modelAssets from the MODEL_BATCH_JOB/MODEL_BATCH_TEST_JOB/MODEL_BATCH_TRAINING_JOB and pass them in as parameters to the function to be executed. These external file assets are passed in as lists of Assets:
- input_data – [{“filename“: “test.csv“, “assetType”: “EXTERNAL_FILE, “fileUrl”: “hdfs:///hadoop/test.csv“}]
- output_data – [{“filename“: “output.csv”, “assetType”: “EXTERNAL_FILE“, “fileUrl”: “hdfs:///hadoop/output.csv“}]
The YarnMonitorService component should be listening for and storing in jobMessage the stdout and stderr produced by the job that is running at the Spark cluster. Whether to store or not store stdout and stderr in jobMessages is configurable.

Architecture Overview

The following diagram represents how core components interact, and gives a high level overview of the process flow from a MODEL_BATCH_JOB/MODEL_BATCH_TEST_JOB/MODEL_BATCH_TRAINING_JOB to a Spark job running at the Spark cluster.

Details

PySpark Dynamic Job Abstraction

ModelOp Center abstracts the process of executing PySpark jobs using MODEL_BATCH_JOB/MODEL_BATCH_TEST_JOB/MODEL_BATCH_TRAINING_JOB as input. The approach uses a main PySpark Driver (ModelOpPySparkDriver.py ) that imports the job metadata (details about job input, output and model assets, as well as the name of the method to be invoked), the model source code to be executed, and then just a simple main that will be able to call the desired function.

######################################################################################## ##### dynamic model / resources content. ######################################################################################## # primary source code import model_source_code as modelop_model_source_code # job metadata, variables pointing to [input, output, appname,etc] import modelop_job_metadata as modelop_job_metadata # for printing stack trace import traceback # for checking number of params in function signature from inspect import signature ######################################################################################## ##### static resources content. ######################################################################################## if __name__ == "__main__": try: print("### - ModelOpPySparkExecution execution") ## Check for an init function to be executed; An init function is optional init_method = getattr(modelop_model_source_code, modelop_job_metadata.init_method_to_be_executed, None) if init_method is None: print("### - Optional init '" + modelop_job_metadata.init_method_to_be_executed + "' function was not found in model source code") else: print("### - Executing function: " + modelop_job_metadata.init_method_to_be_executed) init_method() ## Check for a scoring or metrics function to be executed; A scoring or metrics function is required execution_method = getattr(modelop_model_source_code, modelop_job_metadata.method_to_be_executed, None) if execution_method is None: print("### - '" + modelop_job_metadata.method_to_be_executed + "' function was not found in model source code") raise Exception("### - '" + modelop_job_metadata.method_to_be_executed + "' function was not found in model source code") ## Executing requested function print("### - Executing function: " + modelop_job_metadata.method_to_be_executed) num_params = len(signature(execution_method).parameters) if num_params == 0: execution_method() elif num_params == 3: execution_method(modelop_job_metadata.job_input, modelop_job_metadata.job_output, modelop_job_metadata.job_model_assets_input) else: traceback.print_exc() raise Exception("Number of function parameters, '" + str(num_params) + "', does not match expected number of parameters (0 or 3)") except Exception as e: print("### - An exception of ", e.__class__, " occurred") traceback.print_exc() print("#################### RUNTIME ERROR ####################") raise Exception("### - An exception occurred in the ModelOpPySparkDriver") print("### - PySpark code execution completed")

PySparkJobManifest

ModelOp Center decouples the transformation process that takes a MODEL_BATCH_JOB/MODEL_BATCH_TEST_JOB/MODEL_BATCH_TRAINING_JOB as input and produces a SparkLauncher as output. For this purpose, ModelOp Center uses the PySparkJobManifest intermediate component. PySparkJobManifest contains all the required values when running a spark-submit: Python source code and metadata, function name, application name (all of which are used inside ModelOpPySparkDriver). This design allows us to decouple and to keep agnostic the spark-submit.

The following diagram illustrates the transformation process of a MODEL_BATCH_JOB/MODEL_BATCH_TEST_JOB/MODEL_BATCH_TRAINING_JOB into a SparkLauncher:

ModelOpJobMonitor

The ModelOpJobMonitor has two main responsibilities:

Submitting jobs to the Spark cluster
Monitoring job statuses for existing, waiting and running, Spark jobs.

In order to successfully fulfill these responsibilities, it relies on two key services:

SparkLauncherService – component in charge of translating jobs into SparkLauncher objects
YarnMonitorService – component in charge of fetching job statuses and output produced from the Spark cluster
KerberizedYarnMonitorService – component that is an instance of YarnMonitorService and in charge of authenticating the principal with Kerberos before delegating control to YarnMonitorService

PySpark Job Input and Output Data

The spark-runtime-service supports two types of input and output data for MODEL_BATCH_JOB/MODEL_BATCH_TEST_JOB/MODEL_BATCH_TRAINING_JOB:

HDFS asset(s) by URL a.k.a. External asset(s)
Embedded asset(s) a.k.a. File asset(s)

Input Data by URL

When the user provides HDFS asset(s) by URL as input data for a job, the HDFS asset(s) have to be present at the Spark cluster before the job is submitted to the Spark cluster for execution.

Input Data Embedded

When the user provides embedded input data asset(s), the spark-runtime-service will create a temporary HDFS directory for the job and upload the file content of each embedded input data asset to HDFS. The newly created HDFS file(s) will be represented as HDFS asset(s) by URL and used as the input data when the job is submitted to the Spark cluster for execution.

The change in the input data from embedded asset(s) to HDFS asset(s) by URL is not visible to the user because the MODEL_BATCH_JOB/MODEL_BATCH_TEST_JOB/MODEL_BATCH_TRAINING_JOB is never updated to reflect this change. Instead, the change is handled internally in PySparkPreprocessorService.

Output Data by URL

When the user provides HDFS asset(s) by URL as output data for a job, the job output will be stored at the given HDFS file url.

Output Data Embedded

When the user provides embedded output data asset(s), the spark-runtime-service will create a temporary HDFS directory for the job, if one does not exist yet. Then, the following actions are performed in the given order:

Represent each embedded output data asset as HDFS asset by URL where the file url of the new HDFS asset is the temporary HDFS directory and the filename of the new HDFS asset is the filename of the corresponding embedded asset
Update MODEL_BATCH_JOB/MODEL_BATCH_TEST_JOB/MODEL_BATCH_TRAINING_JOB by storing the HDFS asset(s) by URL in its job parameters Map where the key is TMP_EXTERNAL_OUTPUT
Use the newly created HDFS asset(s) by URL as the output data when the job is submitted to the Spark cluster for execution
Download each HDFS asset by URL and store its content as the file content for the corresponding embedded output data asset in MODEL_BATCH_JOB/MODEL_BATCH_TEST_JOB/MODEL_BATCH_TRAINING_JOB
Remove TMP_EXTERNAL_OUTPUT from the job parameters Map

The change in the output data from embedded asset(s) to HDFS asset(s) by URL is not visible to the user because the MODEL_BATCH_JOB/MODEL_BATCH_TEST_JOB/MODEL_BATCH_TRAINING_JOB is never updated to reflect this change. Instead, the change is handled internally in PySparkPreprocessorService and ModelOpJobMonitor.

For input and output data, the user can have any combination of HDFS asset(s) by URL or embedded asset(s).

PySpark - Metrics Jobs

Running jobs of type MODEL_BATCH_TEST_JOB is one of the key features of the spark-runtime-service. These jobs produce a ModelTestResult whose generation is performed by the MLC.

Spark Details: Spark Submit