Predictor

Which Predictor you use depends on how your model is exported:

• TensorFlow Predictor if your model is exported as a TensorFlow SavedModel

• Python Predictor for all other cases: PyTorch, ONNX, scikit-learn, XGBoost, TensorFlow (if not using SavedModels), etc.

Project files

Cortex makes all files in the project directory (i.e. the directory which contains cortex.yaml) available for use in your Predictor implementation. Python bytecode files (*.pyc, *.pyo, *.pyd), files or folders that start with ., and the api configuration file (e.g. cortex.yaml) are excluded.

The following files can also be added at the root of the project's directory:

• .cortexignore file, which follows the same syntax and behavior as a .gitignore file.

• .env file, which exports environment variables that can be used in the predictor. Each line of this file must follow the VARIABLE=value format.

For example, if your directory looks like this:

./my-classifier/
├── cortex.yaml
├── values.json
├── predictor.py
├── ...
└── requirements.txt

You can access values.json in your Predictor like this:

import json

class PythonPredictor:
    def __init__(self, config):
        with open('values.json', 'r') as values_file:
            values = json.load(values_file)
        self.values = values

Python Predictor

Interface

# initialization code and variables can be declared here in global scope

class PythonPredictor:
    def __init__(self, config, job_spec):
        """(Required) Called once during each worker initialization. Performs
        setup such as downloading/initializing the model or downloading a
        vocabulary.

        Args:
            config (required): Dictionary passed from API configuration (if
                specified) merged with configuration passed in with Job
                Submission API. If there are conflicting keys, values in
                configuration specified in Job submission takes precedence.
            job_spec (optional): Dictionary containing the following fields:
                "job_id": A unique ID for this job
                "api_name": The name of this batch API
                "config": The config that was provided in the job submission
                "workers": The number of workers for this job
                "total_batch_count": The total number of batches in this job
                "start_time": The time that this job started
        """
        pass

    def predict(self, payload, batch_id):
        """(Required) Called once per batch. Preprocesses the batch payload (if
        necessary), runs inference, postprocesses the inference output (if
        necessary), and writes the predictions to storage (i.e. S3 or a
        database, if desired).

        Args:
            payload (required): a batch (i.e. a list of one or more samples).
            batch_id (optional): uuid assigned to this batch.
        Returns:
            Nothing
        """
        pass

    def on_job_complete(self):
        """(Optional) Called once after all batches in the job have been
        processed. Performs post job completion tasks such as aggregating
        results, executing web hooks, or triggering other jobs.
        """
        pass

TensorFlow Predictor

Uses TensorFlow version 2.3.0 by default

Interface

class TensorFlowPredictor:
    def __init__(self, tensorflow_client, config, job_spec):
        """(Required) Called once during each worker initialization. Performs
        setup such as downloading/initializing the model or downloading a
        vocabulary.

        Args:
            tensorflow_client (required): TensorFlow client which is used to
                make predictions. This should be saved for use in predict().
            config (required): Dictionary passed from API configuration (if
                specified) merged with configuration passed in with Job
                Submission API. If there are conflicting keys, values in
                configuration specified in Job submission takes precedence.
            job_spec (optional): Dictionary containing the following fields:
                "job_id": A unique ID for this job
                "api_name": The name of this batch API
                "config": The config that was provided in the job submission
                "workers": The number of workers for this job
                "total_batch_count": The total number of batches in this job
                "start_time": The time that this job started
        """
        self.client = tensorflow_client
        # Additional initialization may be done here

    def predict(self, payload, batch_id):
        """(Required) Called once per batch. Preprocesses the batch payload (if
        necessary), runs inference (e.g. by calling
        self.client.predict(model_input)), postprocesses the inference output
        (if necessary), and writes the predictions to storage (i.e. S3 or a
        database, if desired).

        Args:
            payload (required): a batch (i.e. a list of one or more samples).
            batch_id (optional): uuid assigned to this batch.
        Returns:
            Nothing
        """
        pass

    def on_job_complete(self):
        """(Optional) Called once after all batches in the job have been
        processed. Performs post job completion tasks such as aggregating
        results, executing web hooks, or triggering other jobs.
        """
        pass

Cortex provides a tensorflow_client to your Predictor's constructor. tensorflow_client is an instance of TensorFlowClient that manages a connection to a TensorFlow Serving container to make predictions using your model. It should be saved as an instance variable in your Predictor, and your predict() function should call tensorflow_client.predict() to make an inference with your exported TensorFlow model. Preprocessing of the JSON payload and postprocessing of predictions can be implemented in your predict() function as well.

When multiple models are defined using the Predictor's models field, the tensorflow_client.predict() method expects a second argument model_name which must hold the name of the model that you want to use for inference (for example: self.client.predict(payload, "text-generator")).

If you need to share files between your predictor implementation and the TensorFlow Serving container, you can create a new directory within /mnt (e.g. /mnt/user) and write files to it. The entire /mnt directory is shared between containers, but do not write to any of the directories in /mnt that already exist (they are used internally by Cortex).

Structured logging

You can use Cortex's logger in your predictor implemention to log in JSON. This will enrich your logs with Cortex's metadata, and you can add custom metadata to the logs by adding key value pairs to the extra key when using the logger. For example:

...
from cortex_internal.lib.log import logger as cortex_logger

class PythonPredictor:
    def predict(self, payload, batch_id):
        ...
        cortex_logger.info("completed processing batch", extra={"batch_id": batch_id, "confidence": confidence})

The dictionary passed in via the extra will be flattened by one level. e.g.

{"asctime": "2021-01-19 15:14:05,291", "levelname": "INFO", "message": "completed processing batch", "process": 235, "batch_id": "iuasyd8f7", "confidence": 0.97}

To avoid overriding essential Cortex metadata, please refrain from specifying the following extra keys: asctime, levelname, message, labels, and process. Log lines greater than 5 MB in size will be ignored.

Cortex Python client

A default Cortex Python client environment has been configured for your API. This can be used for deploying/deleting/updating or submitting jobs to your running cluster based on the execution flow of your batch predictor. For example:

import cortex

class PythonPredictor:
    def on_job_complete(self):
        ...
        # get client pointing to the default environment
        client = cortex.client()
        # deploy API in the existing cluster using the artifacts in the previous step
        client.create_api(...)