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Create a serving ready model

To deploy a machine learning model for inference usually involve more than the model artifacts. In most cases, developer has to handle pre-process, post-process and batching for inference. DJL introduces Translator interface to handle most of the boilerplate code and allows developer focus on their model logic.

There are many state-of-the-art models published publicly. Due to the complicity nature of the data processing, developers still need to dig into examples, original training scripts or even contact the original author to figure out how to implement the data processing. DJL provides two ways to address this gap.

ModelZoo

Models in the DJL ModelZoo are ready to use. End user don’t need to worry about data processing. DJL’s ModelZoo allows you easily organize different type of models and their versions. However, creating a custom model zoo isn’t straightforward. We are still working on the tooling to make it easy for model authors to create their own model zoo.

Bundle your data processing scripts together with model artifacts

DJL allows model author to create a ServingTranslator class together with the model artifacts. DJL will load the bundled ServingTranslator and use this class to conduct the data processing.

Step 1: Create a ServingTranslator class

Create a java class that implements ServingTranslator interface. See: MyTranslator as an example.

Step 2: Create a `libs` folder in your model directory

DJL will look into libs folder to search for Translator implementation.

Step 3: Copy Translator into `libs` folder

DJL can load Translator from the following source:

from jar files directly locate in libs folder
from compiled java .class file in libs/classes folder
DJL can compile .java files in libs/classes folder at runtime and load compiled class

Configure data processing based on standard Translator

DJL provides several built-in Translator for well-know ML applications, such as Image Classification and Object Detection. You can customize those built-in Translators’ behavior by providing configuration parameters.

There are two ways to supply configurations to the Translator:

Add a serving.properties file in the model’s folder

Here is an example:

# serving.properties can be used to define model's metadata, all the arguments will be
# passed to TranslatorFactory to create proper Translator

# defines model's application
application=nlp/question_answer

# defines the model's engine, can be overrid by Criteria.optEngine()
engine=PyTorch

# defines TranslatorFactory, can be overrid by Criteria.optTranslator() or Criteria.optTranslatorFactory()
translatorFactory=ai.djl.modality.cv.translator.ImageClassificationTranslatorFactory

# Add Translator specific arguments here to customize pre-processing and post-processing
# specify image size to be cropped
width=224
height=224
# specify the input image should be treated as grayscale image
flag=GRAYSCALE
# specify if apply softmax for post-processing
softmax=true

Pass arguments in Criteria:

You can customize Translator’s behavior with Criteria, for example:

Criteria<Image, Classifications> criteria = Criteria.builder()
        .setTypes(Image.class, Classifications.class) // defines input and output data type
        .optApplication(Application.CV.IMAGE_CLASSIFICATION) // spcific model's application
        .optModelUrls("file:///var/models/my_resnet50") // search models in specified path
        .optArgument("width", 224)
        .optArgument("height", 224)
        .optArgument("height", 224)
        .optArgument("flag", "GRAYSCALE")
        .optArgument("softmax", true)
        .build();

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