PrismRunner - Apache Beam

The PrismRunner is a local portable runner authored in Go that executes Beam pipelines on your machine. It’s designed for fast startup, comprehensive testing, and excellent debugging support.

Overview

PrismRunner provides:

Fast Startup: Quick pipeline execution for rapid development
Portable: Uses the Beam FnAPI to work with all SDKs
Local Execution: Runs on your machine for easy debugging
Testing Focused: Enforces correctness to catch bugs early
Modern Architecture: Built with Go’s concurrency model

When to Use PrismRunner

Best For

Local development
Fast iteration cycles
Testing pipelines
Debugging workflows
Cross-language pipelines
CI/CD testing

Not Suitable For

Production workloads
Large datasets
Distributed processing
Long-running jobs
High-throughput streaming

PrismRunner is designed to eventually replace the DirectRunner for Go SDK users and provide better local testing for all SDKs.

Setup and Configuration

Installation

PrismRunner is automatically downloaded when needed by the Beam SDK:

Java
Python
Go

Add the Prism runner dependency:

<dependency>
  <groupId>org.apache.beam</groupId>
  <artifactId>beam-runners-prism-java</artifactId>
  <version>{beam-version}</version>
</dependency>

For Gradle:

implementation 'org.apache.beam:beam-runners-prism-java:{beam-version}'

Install Beam with Prism support:

pip install apache-beam

Prism binary is automatically managed by the SDK.

Import the Prism runner:

import "github.com/apache/beam/sdks/v2/go/pkg/beam/runners/prism"

Or install the Prism binary directly:

go install github.com/apache/beam/sdks/v2/go/cmd/prism@latest

Manual Installation

You can also install Prism manually:

# Download from GitHub releases
wget https://github.com/apache/beam/releases/download/v{version}/prism-{os}-{arch}.zip
unzip prism-{os}-{arch}.zip

# Or build from source
git clone https://github.com/apache/beam.git
cd beam/sdks/go/cmd/prism
go build

Running a Pipeline

Basic Usage

Java
Python
Go

import org.apache.beam.runners.prism.PrismRunner;
import org.apache.beam.runners.prism.PrismPipelineOptions;
import org.apache.beam.sdk.Pipeline;
import org.apache.beam.sdk.options.PipelineOptionsFactory;

public class MyPrismPipeline {
  public static void main(String[] args) {
    PrismPipelineOptions options = 
        PipelineOptionsFactory.fromArgs(args)
            .withValidation()
            .as(PrismPipelineOptions.class);
    
    // Set the runner
    options.setRunner(PrismRunner.class);
    
    Pipeline p = Pipeline.create(options);
    
    // Build your pipeline
    p.apply(/* your transforms */);
    
    // Execute with Prism
    p.run().waitUntilFinish();
  }
}

import apache_beam as beam
from apache_beam.options.pipeline_options import PipelineOptions

def run():
    options = PipelineOptions([
        '--runner=PrismRunner',
    ])
    
    with beam.Pipeline(options=options) as p:
        # Build your pipeline
        (p 
         | beam.Create(['Hello', 'Prism'])
         | beam.Map(lambda x: x.upper())
         | beam.Map(print))

if __name__ == '__main__':
    run()

package main

import (
    "context"
    
    "github.com/apache/beam/sdks/v2/go/pkg/beam"
    "github.com/apache/beam/sdks/v2/go/pkg/beam/runners/prism"
)

func main() {
    beam.Init()
    
    p := beam.NewPipeline()
    s := p.Root()
    
    // Build your pipeline
    data := beam.Create(s, "Hello", "Prism")
    // ... more transforms
    
    if err := prism.Execute(context.Background(), p); err != nil {
        panic(err)
    }
}

Command Line

Run with PrismRunner from the command line:

# Java
mvn compile exec:java -Dexec.mainClass=com.example.MyPipeline \
  -Dexec.args="--runner=PrismRunner"

# Python
python my_pipeline.py --runner=PrismRunner

# Go
go run my_pipeline.go --runner=prism

PrismPipelineOptions

Configure PrismRunner with these options:

Core Options

prismLocation

string

Path or URL to the Prism binary. If not set, the SDK will auto-download it.

options.setPrismLocation("/path/to/prism");

Can be:

Local file path: /usr/local/bin/prism
URL to binary: https://example.com/prism
GitHub release URL: Auto-constructs download URL

prismVersionOverride

string

Override the SDK version for downloading Prism from GitHub releases.

options.setPrismVersionOverride("2.50.0");

enableWebUI

boolean

default:"true"

Enable the Prism Web UI for monitoring.

options.setEnableWebUI(true);

Access at http://localhost:8080 when enabled.

idleShutdownTimeout

string

default:"5m"

Duration Prism waits for a new job before shutting down. Negative durations disable auto-shutdown.

options.setIdleShutdownTimeout("10m");

Valid time units: ns, us, ms, s, m, h

prismLogLevel

string

default:"warn"

Log level for Prism: debug, info, warn, or error.

options.setPrismLogLevel("info");

Features and Capabilities

Supported Transforms

✅ ParDo: All DoFn features
✅ GroupByKey: Including session windows
✅ CoGroupByKey: Multi-input grouping
✅ Combine: Lifted and unlifted
✅ Flatten: Multiple PCollections
✅ Side Inputs: All side input patterns
✅ Windowing: Fixed, sliding, session, global

Windowing Support

import org.apache.beam.sdk.transforms.windowing.*;

pipeline
    .apply(/* source */)
    .apply(Window.<String>into(
        FixedWindows.of(Duration.standardMinutes(1))))
    .apply(/* transforms */);

Supported window types:

Global windows
Fixed windows
Sliding windows
Session windows

State and Timers

State and timers support is limited in the current version of PrismRunner.

Splittable DoFn

PrismRunner expands Splittable DoFns:

public class MySplittableDoFn extends DoFn<String, String> {
  @ProcessElement
  public void processElement(
      @Element String element,
      RestrictionTracker<OffsetRange, Long> tracker,
      OutputReceiver<String> out) {
    // Splittable processing
  }
  
  @GetInitialRestriction
  public OffsetRange getInitialRestriction(@Element String element) {
    return new OffsetRange(0, element.length());
  }
}

Web UI

PrismRunner includes a built-in web UI for monitoring:

Accessing the UI

When enableWebUI is true:

Start your pipeline with PrismRunner
Open http://localhost:8080 in your browser
View job progress, metrics, and logs

Features

Job status and progress
Transform graph visualization
Metrics and counters
Error messages and logs
Watermark tracking

The Web UI is particularly useful for debugging complex pipelines and understanding execution flow.

Testing with PrismRunner

PrismRunner is excellent for testing:

Unit Tests

Java
Python
Go

import org.apache.beam.sdk.testing.TestPipeline;
import org.apache.beam.sdk.testing.PAssert;
import org.junit.Rule;
import org.junit.Test;

public class MyPipelineTest {
  @Rule
  public final transient TestPipeline pipeline = 
      TestPipeline.fromOptions(
          PipelineOptionsFactory.create()
              .as(PrismPipelineOptions.class));
  
  @Test
  public void testWithPrism() {
    PrismPipelineOptions options = 
        pipeline.getOptions().as(PrismPipelineOptions.class);
    options.setRunner(PrismRunner.class);
    
    PCollection<String> output = pipeline
        .apply(Create.of("Hello", "World"))
        .apply(MapElements.into(TypeDescriptors.strings())
            .via(String::toUpperCase));
    
    PAssert.that(output).containsInAnyOrder("HELLO", "WORLD");
    
    pipeline.run();
  }
}

import unittest
import apache_beam as beam
from apache_beam.testing.test_pipeline import TestPipeline
from apache_beam.testing.util import assert_that, equal_to
from apache_beam.options.pipeline_options import PipelineOptions

class MyPipelineTest(unittest.TestCase):
    def test_with_prism(self):
        options = PipelineOptions([
            '--runner=PrismRunner',
        ])
        
        with TestPipeline(options=options) as p:
            output = (
                p 
                | beam.Create(['Hello', 'World'])
                | beam.Map(str.upper)
            )
            
            assert_that(output, equal_to(['HELLO', 'WORLD']))

package main

import (
    "context"
    "testing"
    
    "github.com/apache/beam/sdks/v2/go/pkg/beam"
    "github.com/apache/beam/sdks/v2/go/pkg/beam/runners/prism"
    "github.com/apache/beam/sdks/v2/go/pkg/beam/testing/passert"
)

func TestPipeline(t *testing.T) {
    p, s := beam.NewPipelineWithRoot()
    
    input := beam.Create(s, "Hello", "World")
    output := /* transforms */
    
    passert.Equals(s, output, "HELLO", "WORLD")
    
    if err := prism.Execute(context.Background(), p); err != nil {
        t.Fatalf("Pipeline failed: %v", err)
    }
}

Integration Tests

PrismRunner is ideal for CI/CD integration tests:

# GitHub Actions example
name: Test Pipeline

on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      
      - name: Set up Java
        uses: actions/setup-java@v2
        with:
          java-version: '11'
      
      - name: Run tests with Prism
        run: |
          mvn test -Dtest=MyPipelineTest \
            -Drunner=PrismRunner

Debugging

PrismRunner provides excellent debugging support:

Local Debugging

Since Prism runs locally, you can:

Set breakpoints in your DoFns
Use your IDE’s debugger
Inspect variables in real-time
Step through pipeline execution

Logging

Java
Python
Go

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class MyDoFn extends DoFn<String, String> {
  private static final Logger LOG = LoggerFactory.getLogger(MyDoFn.class);
  
  @ProcessElement
  public void processElement(ProcessContext c) {
    LOG.info("Processing: {}", c.element());
    c.output(c.element());
  }
}

import logging

class MyDoFn(beam.DoFn):
    def process(self, element):
        logging.info(f'Processing: {element}')
        yield element.upper()

import "github.com/apache/beam/sdks/v2/go/pkg/beam/log"

func processElement(ctx context.Context, element string) string {
    log.Infof(ctx, "Processing: %s", element)
    return element
}

Prism Logs

Control Prism’s own logging:

PrismPipelineOptions options = 
    PipelineOptionsFactory.as(PrismPipelineOptions.class);

// Set to debug for detailed Prism internals
options.setPrismLogLevel("debug");

Portable Architecture

PrismRunner uses Beam’s portable architecture:

How It Works

Pipeline Translation: SDK translates pipeline to portable proto
Job Submission: Prism receives the job via FnAPI
SDK Harness: Prism launches SDK-specific workers
Execution: Prism coordinates execution across workers
Results: Results are returned to the client

Cross-Language Support

PrismRunner supports cross-language pipelines:

// Java pipeline using Python transform
pipeline
    .apply(Create.of("data"))
    .apply("PythonTransform", 
        PythonExternalTransform.from("my_transform"))
    .apply(/* more Java transforms */);

Performance Considerations

PrismRunner is optimized for development, not production:

Memory: All data processed in memory
Single Machine: No distributed execution
Fast Startup: Quick iteration for development
Testing Focus: Prioritizes correctness over speed

For production workloads or large datasets, use DataflowRunner, FlinkRunner, or SparkRunner.

Comparison with DirectRunner

Feature	PrismRunner	DirectRunner
Architecture	Portable/FnAPI	SDK-specific
Languages	All SDKs	Per-SDK
Startup Time	Fast	Fast
Cross-language	Yes	No
Web UI	Yes	No
State	Limited	Full
Maturity	Newer	Mature

Current Limitations

PrismRunner is under active development. Some limitations:

Testing Use Only: Not for production workloads
In-Memory Only: Not suitable for large jobs
Limited State: State and timers support is incomplete
Single Machine: No distributed execution
Feature Coverage: Some Beam features not yet implemented

See the Prism README for current status.

Future Roadmap

Upcoming features:

Complete state and timers support
Triggers and complex windowing
Test Stream support
Container execution for cross-language
Better streaming support
Performance optimizations

Best Practices

Development Workflow

Start with PrismRunner for development

python my_pipeline.py --runner=PrismRunner

Test with DirectRunner for comprehensive validation
```
python my_pipeline.py --runner=DirectRunner
```

Deploy with production runner

python my_pipeline.py --runner=DataflowRunner \
  --project=my-project \
  --region=us-central1

Testing Strategy

Use PrismRunner for fast unit tests
Use DirectRunner for thorough validation tests
Use production runner for integration tests

CI/CD Integration

# Use PrismRunner for fast CI tests
- name: Fast Tests
  run: mvn test -Drunner=PrismRunner

# Use DirectRunner for thorough validation
- name: Validation Tests
  run: mvn verify -Drunner=DirectRunner

Troubleshooting

Prism binary not found

The SDK will auto-download Prism. If this fails:Check internet connectivity
Manually download from GitHub releases
Set --prismLocation to local binary

Web UI not accessible

Ensure --enableWebUI=true
Check port 8080 is not in use
Verify firewall settings

Pipeline fails with 'feature not implemented'

Check Prism’s current feature support
Consider using DirectRunner instead
Report the issue on GitHub

Slow execution

Reduce data size for local testing
Check for inefficient transforms
Consider using a distributed runner for large data

Next Steps

Prism GitHub

View source and contribute

DirectRunner

Alternative local runner

Testing Guide

Learn more about testing

Cross-Language

Build multi-language pipelines

Getting Started

Core Concepts

SDKs

Runners

I/O Connectors

Documentation Index

​Overview

​When to Use PrismRunner

Best For

Not Suitable For

​Setup and Configuration

​Installation

​Manual Installation

​Running a Pipeline

​Basic Usage

​Command Line

​PrismPipelineOptions

​Core Options

​Features and Capabilities

​Supported Transforms

​Windowing Support

​State and Timers

​Splittable DoFn

​Web UI

​Accessing the UI

​Features

​Testing with PrismRunner

​Unit Tests

​Integration Tests

​Debugging

​Local Debugging

​Logging

​Prism Logs

​Portable Architecture

​How It Works

​Cross-Language Support

​Performance Considerations

​Comparison with DirectRunner

​Current Limitations

​Future Roadmap

​Best Practices

​Development Workflow

​Testing Strategy

​CI/CD Integration

​Troubleshooting

​Next Steps

Prism GitHub

DirectRunner

Testing Guide

Cross-Language

Build docs developers (and LLMs) love

Overview

When to Use PrismRunner

Setup and Configuration

Installation

Manual Installation

Running a Pipeline

Basic Usage

Command Line

PrismPipelineOptions

Core Options

Features and Capabilities

Supported Transforms

Windowing Support

State and Timers

Splittable DoFn

Web UI

Accessing the UI

Features

Testing with PrismRunner

Unit Tests

Integration Tests

Debugging

Local Debugging

Logging

Prism Logs

Portable Architecture

How It Works

Cross-Language Support

Performance Considerations

Comparison with DirectRunner

Current Limitations

Future Roadmap

Best Practices

Development Workflow

Testing Strategy

CI/CD Integration

Troubleshooting

Next Steps