Predictor implementation

Once your model is exported, you can implement one of Cortex's Predictor classes to deploy your model. A Predictor is a Python class that describes how to initialize your model and use it to make predictions.

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

The response type of the predictor can vary depending on your requirements, see API responses below.

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):
"""(Required) Called once before the API becomes available. Performs
setup such as downloading/initializing the model or downloading a
vocabulary.
Args:
config (required): Dictionary passed from API configuration (if
specified). This may contain information on where to download
the model and/or metadata.
"""
pass
def predict(self, payload, query_params, headers):
"""(Required) Called once per request. Preprocesses the request payload
(if necessary), runs inference, and postprocesses the inference output
(if necessary).
Args:
payload (optional): The request payload (see below for the possible
payload types).
query_params (optional): A dictionary of the query parameters used
in the request.
headers (optional): A dictionary of the headers sent in the request.
Returns:
Prediction or a batch of predictions.
"""
pass
def post_predict(self, response, payload, query_params, headers):
"""(Optional) Called in the background after returning a response.
Useful for tasks that the client doesn't need to wait on before
receiving a response such as recording metrics or storing results.
Args:
response (optional): The response as returned by the predict method.
payload (optional): The request payload (see below for the possible
payload types).
query_params (optional): A dictionary of the query parameters used
in the request.
headers (optional): A dictionary of the headers sent in the request.
"""
pass

For proper separation of concerns, it is recommended to use the constructor's config parameter for information such as from where to download the model and initialization files, or any configurable model parameters. You define config in your API configuration, and it is passed through to your Predictor's constructor.

Your API can accept requests with different types of payloads such as JSON-parseable, bytes or starlette.datastructures.FormData data. Navigate to the API requests section to learn about how headers can be used to change the type of payload that is passed into your predict method.

Your predictor method can return different types of objects such as JSON-parseable, string, and bytes objects. Navigate to the API responses section to learn about how to configure your predictor method to respond with different response codes and content-types.

Examples

Many of the examples use the Python Predictor, including all of the PyTorch examples.

Here is the Predictor for examples/pytorch/text-generator:

import torch
from transformers import GPT2Tokenizer, GPT2LMHeadModel
class PythonPredictor:
def __init__(self, config):
self.device = "cuda" if torch.cuda.is_available() else "cpu"
print(f"using device: {self.device}")
self.tokenizer = GPT2Tokenizer.from_pretrained("gpt2")
self.model = GPT2LMHeadModel.from_pretrained("gpt2").to(self.device)
def predict(self, payload):
input_length = len(payload["text"].split())
tokens = self.tokenizer.encode(payload["text"], return_tensors="pt").to(self.device)
prediction = self.model.generate(tokens, max_length=input_length + 20, do_sample=True)
return self.tokenizer.decode(prediction[0])

Pre-installed packages

The following Python packages are pre-installed in Python Predictors and can be used in your implementations:

boto3==1.13.7
cloudpickle==1.4.1
Cython==0.29.17
dill==0.3.1.1
fastapi==0.54.1
joblib==0.14.1
Keras==2.3.1
msgpack==1.0.0
nltk==3.5
np-utils==0.5.12.1
numpy==1.18.4
opencv-python==4.2.0.34
pandas==1.0.3
Pillow==7.1.2
pyyaml==5.3.1
requests==2.23.0
scikit-image==0.17.1
scikit-learn==0.22.2.post1
scipy==1.4.1
six==1.14.0
statsmodels==0.11.1
sympy==1.5.1
tensorflow-hub==0.8.0
tensorflow==2.1.0
torch==1.5.0
torchvision==0.6.0
xgboost==1.0.2

Inferentia-equipped APIs

The list is slightly different for inferentia-equipped APIs:

boto3==1.13.7
cloudpickle==1.3.0
Cython==0.29.17
dill==0.3.1.1
fastapi==0.54.1
joblib==0.14.1
msgpack==1.0.0
neuron-cc==1.0.9410.0+6008239556
nltk==3.4.5
np-utils==0.5.12.1
numpy==1.16.5
opencv-python==4.2.0.32
pandas==1.0.3
Pillow==6.2.2
pyyaml==5.3.1
requests==2.23.0
scikit-image==0.16.2
scikit-learn==0.22.2.post1
scipy==1.3.2
six==1.14.0
statsmodels==0.11.1
sympy==1.5.1
tensorflow-neuron==1.15.0.1.0.1333.0
torch-neuron==1.0.825.0
torchvision==0.4.2

The pre-installed system packages are listed in images/python-predictor-cpu/Dockerfile (for CPU), images/python-predictor-gpu/Dockerfile (for GPU), or images/python-predictor-inf/Dockerfile (for Inferentia).

If your application requires additional dependencies, you can install additional Python packages and system packages.

TensorFlow Predictor

Interface

class TensorFlowPredictor:
def __init__(self, tensorflow_client, config):
"""(Required) Called once before the API becomes available. Performs
setup such as downloading/initializing 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).
"""
self.client = tensorflow_client
# Additional initialization may be done here
def predict(self, payload, query_params, headers):
"""(Required) Called once per request. Preprocesses the request payload
(if necessary), runs inference (e.g. by calling
self.client.predict(model_input)), and postprocesses the inference
output (if necessary).
Args:
payload (optional): The request payload (see below for the possible
payload types).
query_params (optional): A dictionary of the query parameters used
in the request.
headers (optional): A dictionary of the headers sent in the request.
Returns:
Prediction or a batch of predictions.
"""
pass
def post_predict(self, response, payload, query_params, headers):
"""(Optional) Called in the background after returning a response.
Useful for tasks that the client doesn't need to wait on before
receiving a response such as recording metrics or storing results.
Args:
response (optional): The response as returned by the predict method.
payload (optional): The request payload (see below for the possible
payload types).
query_params (optional): A dictionary of the query parameters used
in the request.
headers (optional): A dictionary of the headers sent in the request.
"""
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")). See the multi model guide for more information.

For proper separation of concerns, it is recommended to use the constructor's config parameter for information such as configurable model parameters or download links for initialization files. You define config in your API configuration, and it is passed through to your Predictor's constructor.

Your API can accept requests with different types of payloads such as JSON-parseable, bytes or starlette.datastructures.FormData data. Navigate to the API requests section to learn about how headers can be used to change the type of payload that is passed into your predict method.

Your predictor method can return different types of objects such as JSON-parseable, string, and bytes objects. Navigate to the API responses section to learn about how to configure your predictor method to respond with different response codes and content-types.

Examples

Most of the examples in examples/tensorflow use the TensorFlow Predictor.

Here is the Predictor for examples/tensorflow/iris-classifier:

labels = ["setosa", "versicolor", "virginica"]
class TensorFlowPredictor:
def __init__(self, tensorflow_client, config):
self.client = tensorflow_client
def predict(self, payload):
prediction = self.client.predict(payload)
predicted_class_id = int(prediction["class_ids"][0])
return labels[predicted_class_id]

Pre-installed packages

The following Python packages are pre-installed in TensorFlow Predictors and can be used in your implementations:

boto3==1.13.7
dill==0.3.1.1
fastapi==0.54.1
msgpack==1.0.0
numpy==1.18.4
opencv-python==4.2.0.34
pyyaml==5.3.1
requests==2.23.0
tensorflow-hub==0.8.0
tensorflow-serving-api==2.1.0
tensorflow==2.1.0

The pre-installed system packages are listed in images/tensorflow-predictor/Dockerfile.

If your application requires additional dependencies, you can install additional Python packages and system packages.

ONNX Predictor

Interface

class ONNXPredictor:
def __init__(self, onnx_client, config):
"""(Required) Called once before the API becomes available. Performs
setup such as downloading/initializing a vocabulary.
Args:
onnx_client (required): ONNX client which is used to make
predictions. This should be saved for use in predict().
config (required): Dictionary passed from API configuration (if
specified).
"""
self.client = onnx_client
# Additional initialization may be done here
def predict(self, payload, query_params, headers):
"""(Required) Called once per request. Preprocesses the request payload
(if necessary), runs inference (e.g. by calling
self.client.predict(model_input)), and postprocesses the inference
output (if necessary).
Args:
payload (optional): The request payload (see below for the possible
payload types).
query_params (optional): A dictionary of the query parameters used
in the request.
headers (optional): A dictionary of the headers sent in the request.
Returns:
Prediction or a batch of predictions.
"""
pass
def post_predict(self, response, payload, query_params, headers):
"""(Optional) Called in the background after returning a response.
Useful for tasks that the client doesn't need to wait on before
receiving a response such as recording metrics or storing results.
Args:
response (optional): The response as returned by the predict method.
payload (optional): The request payload (see below for the possible
payload types).
query_params (optional): A dictionary of the query parameters used
in the request.
headers (optional): A dictionary of the headers sent in the request.
"""
pass

Cortex provides an onnx_client to your Predictor's constructor. onnx_client is an instance of ONNXClient that manages an ONNX Runtime session to make predictions using your model. It should be saved as an instance variable in your Predictor, and your predict() function should call onnx_client.predict() to make an inference with your exported ONNX 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 onnx_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(model_input, "text-generator")). See the multi model guide for more information.

For proper separation of concerns, it is recommended to use the constructor's config parameter for information such as configurable model parameters or download links for initialization files. You define config in your API configuration, and it is passed through to your Predictor's constructor.

Your API can accept requests with different types of payloads such as JSON-parseable, bytes or starlette.datastructures.FormData data. Navigate to the API requests section to learn about how headers can be used to change the type of payload that is passed into your predict method.

Your predictor method can return different types of objects such as JSON-parseable, string, and bytes objects. Navigate to the API responses section to learn about how to configure your predictor method to respond with different response codes and content-types.

Examples

examples/onnx/iris-classifier uses the ONNX Predictor:

labels = ["setosa", "versicolor", "virginica"]
class ONNXPredictor:
def __init__(self, onnx_client, config):
self.client = onnx_client
def predict(self, payload):
model_input = [
payload["sepal_length"],
payload["sepal_width"],
payload["petal_length"],
payload["petal_width"],
]
prediction = self.client.predict(model_input)
predicted_class_id = prediction[0][0]
return labels[predicted_class_id]

Pre-installed packages

The following Python packages are pre-installed in ONNX Predictors and can be used in your implementations:

boto3==1.13.7
dill==0.3.1.1
fastapi==0.54.1
msgpack==1.0.0
numpy==1.18.4
onnxruntime==1.2.0
pyyaml==5.3.1
requests==2.23.0

The pre-installed system packages are listed in images/onnx-predictor-cpu/Dockerfile (for CPU) or images/onnx-predictor-gpu/Dockerfile (for GPU).

If your application requires additional dependencies, you can install additional Python packages and system packages.

API requests

The type of the payload parameter in predict(self, payload) can vary based on the content type of the request. The payload parameter is parsed according to the Content-Type header in the request:

  1. For Content-Type: application/json, payload will be the parsed JSON body.

  2. For Content-Type: multipart/form-data / Content-Type: application/x-www-form-urlencoded, payload will be starlette.datastructures.FormData (key-value pairs where the value is a string for form data, or starlette.datastructures.UploadFile for file uploads, see Starlette's documentation).

  3. For all other Content-Type values, payload will be the raw bytes of the request body.

The payload parameter type will be a Python object (lists, dicts, numbers) if a request with a JSON payload is made:

$ curl http://***.amazonaws.com/my-api \
-X POST -H "Content-Type: application/json" \
-d '{"key": "value"}'

The payload parameter type will be a bytes object if a request with a Content-Type: application/octet-stream is made:

$ curl http://***.amazonaws.com/my-api \
-X POST -H "Content-Type: application/octet-stream" \
-d @file.bin

The payload parameter type will be a bytes object if a request doesn't have the Content-Type set:

$ curl http://***.amazonaws.com/my-api \
-X POST -H "Content-Type:" \
-d @sample.txt

The payload parameter type will be a starlette.datastructures.FormData object if a request with a Content-Type: multipart/form-data is made:

$ curl http://***.amazonaws.com/my-api \
-X POST -H "Content-Type: multipart/form-data" \
-F "fieldName=@file.txt"

The payload parameter type will be a starlette.datastructures.FormData object if a request with a Content-Type: application/x-www-form-urlencoded is made:

$ curl http://***.amazonaws.com/my-api \
-X POST -H "Content-Type: application/x-www-form-urlencoded" \
-d @file.txt

The payload parameter type will be a starlette.datastructures.FormData object if no headers are added to the request:

$ curl http://***.amazonaws.com/my-api \
-X POST \
-d @file.txt

API responses

The response of your predict() function may be:

  1. A JSON-serializable object (lists, dictionaries, numbers, etc.)

  2. A string object (e.g. "class 1")

  3. A bytes object (e.g. bytes(4) or pickle.dumps(obj))

Here are some examples:

def predict(self, payload):
# json-serializable object
response = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
return response
def predict(self, payload):
# string object
response = "class 1"
return response
def predict(self, payload):
# bytes-like object
array = np.random.randn(3, 3)
response = pickle.dumps(array)
return response
def predict(self, payload):
# starlette.responses.Response
data = "class 1"
response = starlette.responses.Response(
content=data, media_type="text/plain")
return response