Multi-model pipelines

Apache Beam allows you to develop multi-model pipelines. This example demonstrates how to ingest and transform input data, run it through a model, and then pass the outcome of your first model into a second model. This page explains how multi-model pipelines work and gives an overview of what you need to know to build one.

Before reading this section, it is recommended that you become familiar with the information in the Pipeline development lifecycle.

How to build a Multi-model pipeline with Beam

A typical machine learning workflow involves a series of data transformation steps, such as data ingestion, data processing tasks, inference, and post-processing. Apache Beam enables you to orchestrate all of those steps together by encapsulating them in a single Apache Beam Directed Acyclic Graph (DAG), which allows you to build resilient and scalable end-to-end machine learning systems.

To deploy your machine learning model in an Apache Beam pipeline, use the RunInferenceAPI, which facilitates the integration of your model as a PTransform step in your DAG. Composing multiple RunInference transforms within a single DAG makes it possible to build a pipeline that consists of multiple ML models. In this way, Apache Beam supports the development of complex ML systems.

You can use different patterns to build multi-model pipelines in Apache Beam. This page explores A/B patterns and cascade patterns.

A/B Pattern

The A/B pattern describes a framework multiple where ML models are running in parallel. One application for this pattern is to test the performance of different machine learning models and decide whether a new model is an improvement over an existing one. This is also known as the “Champion/Challenger” method. Typically, you define a business metric to compare the performance of a control model with the current model.

An example could be recommendation engine models where you have an existing model that recommends ads based on the user’s preferences and activity history. When deciding to deploy a new model, you could split the incoming user traffic into two branches, where half of the users are exposed to the new model and the other half to the current one.

After, you can measure the average click-through rate (CTR) of ads for both sets of users over a defined period of time to determine if the new model is performing better than the existing one.

import apache_beam as beam

with beam.Pipeline() as pipeline:
   userset_a_traffic, userset_b_traffic =
     (pipeline | 'ReadFromStream' >> beam.ReadFromStream('stream_source')
               | ‘Partition’ >> beam.partition(split_dataset, 2, ratio=[5, 5])

model_a_predictions = userset_a_traffic | RunInference(<model_handler_A>)
model_b_predictions = userset_b_traffic | RunInference(<model_handler_B>)

Where beam.partition is used to split the data source into 50/50 split partitions. For more information about data partitioning, see Partition.

Cascade Pattern

The Cascade pattern is used when the solution to a problem involves a series of ML models. In this scenario, the output of a model is typically transformed to a suitable format using a PTransform before passing it to another model.

with pipeline as p:
   data = p | 'Read' >> beam.ReadFromSource('a_source')
   model_a_predictions = data | RunInference(<model_handler_A>)
   model_b_predictions = model_a_predictions | beam.ParDo(post_processing()) | RunInference(<model_handler_B>)

The Ensemble model using an image captioning and ranking example notebook shows an end-to-end example of a cascade pipeline used to generate and rank image captions. The solution consists of two open-source models:

  1. A caption generation model (BLIP) that generates candidate image captions from an input image.
  2. A caption ranking model (CLIP) that uses the image and candidate captions to rank the captions in the order in which they best describe the image.