An MLflow Model is a standard format for packaging machine learning models that can be used in a variety of downstream tools—for example, real-time serving through a REST API or batch inference on Apache Spark. The format defines a convention that lets you save a model in different “flavors” that can be understood by different downstream tools.
Table of Contents
Each MLflow Model is a directory containing arbitrary files, together with an
file in the root of the directory that can define multiple flavors that the model can be viewed
Flavors are the key concept that makes MLflow Models powerful: they are a convention that deployment
tools can use to understand the model, which makes it possible to write tools that work with models
from any ML library without having to integrate each tool with each library. MLflow defines
several “standard” flavors that all of its built-in deployment tools support, such as a “Python
function” flavor that describes how to run the model as a Python function. However, libraries can
also define and use other flavors. For example, MLflow’s
mlflow.sklearn library allows
loading models back as a scikit-learn
Pipeline object for use in code that is aware of
scikit-learn, or as a generic Python function for use in tools that just need to apply the model
(for example, the
mlflow sagemaker tool for deploying models to Amazon SageMaker).
All of the flavors that a particular model supports are defined in its
MLmodel file in YAML
format. For example,
mlflow.sklearn outputs models as follows:
# Directory written by mlflow.sklearn.save_model(model, "my_model") my_model/ ├── MLmodel └── model.pkl
MLmodel file describes two flavors:
time_created: 2018-05-25T17:28:53.35 flavors: sklearn: sklearn_version: 0.19.1 pickled_model: model.pkl python_function: loader_module: mlflow.sklearn
This model can then be used with any tool that supports either the
python_function model flavor. For example, the
mlflow sklearn command can serve a
model with the
mlflow sklearn serve my_model
In addition, the
mlflow sagemaker command-line tool can package and deploy models to AWS
SageMaker as long as they support the
mlflow sagemaker deploy -m my_model [other options]
Fields in the MLmodel Format
Apart from a flavors field listing the model flavors, the MLmodel YAML format can contain the following fields:
- Date and time when the model was created, in UTC ISO 8601 format.
- ID of the run that created the model, if the model was saved using MLflow Tracking.
You can save and load MLflow Models in multiple ways. First, MLflow includes integrations with
several common libraries. For example,
load_model functions for scikit-learn models. Second,
you can use the
mlflow.models.Model class to create and write models. This
class has four key functions:
add_flavorto add a flavor to the model. Each flavor has a string name and a dictionary of key-value attributes, where the values can be any object that can be serialized to YAML.
saveto save the model to a local directory.
logto log the model as an artifact in the current run using MLflow Tracking.
loadto load a model from a local directory or from an artifact in a previous run.
Built-In Model Flavors
MLflow provides several standard flavors that might be useful in your applications. Specifically, many of its deployment tools support these flavors, so you can export your own model in one of these flavors to benefit from all these tools.
Python Function (
python_function model flavor defines a generic filesystem format for Python models and provides utilities
for saving and loading models to and from this format. The format is self-contained in the sense
that it includes all the information necessary to load and use a model. Dependencies
are stored either directly with the model or referenced via Conda environment.
The convention for
python_function models is to have a
predict method or function with the following
predict(data: pandas.DataFrame) -> [pandas.DataFrame | numpy.array]
Other MLflow components expect
python_function models to follow this convention.
python_function model format is defined as a directory structure containing all required data, code, and
./dst-path/ ./MLmodel: configuration <code>: code packaged with the model (specified in the MLmodel file) <data>: data packaged with the model (specified in the MLmodel file) <env>: Conda environment definition (specified in the MLmodel file)
python_function model directory must contain an
MLmodel file in its root with “python_function” format and the following parameters:
- loader_module [required]:
Python module that can load the model. Expected to be a module identifier (for example,
mlflow.sklearn) importable via
importlib.import_module. The imported module must contain a function with the following signature:
load_pyfunc(path: string) -> <pyfunc model>
The path argument is specified by the
dataparameter and may refer to a file or directory.
- code [optional]:
A relative path to a directory containing the code packaged with this model. All files and directories inside this directory are added to the Python path prior to importing the model loader.
- data [optional]:
A relative path to a file or directory containing model data. The path is passed to the model loader.
- env [optional]:
A relative path to an exported Conda environment. If present this environment is activated prior to running the model.
├── MLmodel ├── code │ ├── sklearn_iris.py │ ├── data │ └── model.pkl └── mlflow_env.yml
python_function: code: code data: data/model.pkl loader_module: mlflow.sklearn env: mlflow_env.yml main: sklearn_iris
For more information, see
The H2O model flavor enables logging and loading H2O models. These models will be saved by using the
mlflow.h2o.log_model will also enable a valid
Python Function flavor.
When loading a H2O model as a PyFunc model,
h2o.init(...) will be called. Therefore, the right version of h2o(-py) has to be in the environment. The arguments given to
h2o.init(...) can be customized in
model.h2o/h2o.yaml under the key
init. For more information, see
keras model flavor enables logging and loading Keras models. This model will be saved in a HDF5 file format, via the model_save functionality provided by Keras. Additionally, model can be loaded back as
Python Function. For more information, see
mleap model flavor supports saving models using the MLeap persistence mechanism. A companion module for loading MLflow models with the MLeap flavor format is available in the
mlflow/java package. For more information, see
pytorch model flavor enables logging and loading PyTorch models. Model is completely stored in .pth format using torch.save(model) method. Given a directory containing a saved model, you can log the model to MLflow via
log_saved_model. The saved model can then be loaded for inference via
load_pyfunc(). For more information, see
sklearn model flavor provides an easy to use interface for handling scikit-learn models with no
external dependencies. It saves and loads models using Python’s pickle module and also generates a valid
python_function flavor model. For more information, see
Spark MLlib (
spark model flavor enables exporting Spark MLlib models as MLflow models. Exported models are
saved using Spark MLLib’s native serialization, and can then be loaded back as MLlib models or
python_function models. When deployed as a
python_function, the model creates its own
SparkContext and converts pandas DataFrame input to a Spark DataFrame before scoring. While this is not
the most efficient solution, especially for real-time scoring, it enables you to easily deploy any MLlib PipelineModel
(as long as the PipelineModel has no external JAR dependencies) to any endpoint supported by
MLflow. For more information, see
tensorflow model flavor enables logging TensorFlow
Saved Models and loading them back as
Python Function models for inference on pandas DataFrames. Given a directory containing a saved model, you can log the model to MLflow via
log_saved_model and then load the saved model for inference using
load_pyfunc. For more information, see
You can add a flavor in MLmodel files, either by writing it directly or
building it with the
mlflow.models.Model class. Choose an arbitrary string name
for your flavor. MLflow tools ignore flavors in the MLmodel file that they do not understand.
Built-In Deployment Tools
MLflow provides tools for deploying models on a local machine and several production environments. You can use these tools to easily apply your models in a production environment. Not all deployment methods are available for all model flavors. Deployment is supported for the Python function format and all compatible formats.
MLflow can deploy models locally as local REST API endpoints or to directly score CSV files.
This functionality is a convenient way of testing models before uploading to a remote model server.
You deploy the Python Function flavor locally via the CLI interface to the
servedeploys the model as a local REST API server.
predictuses the model to generate a prediction for a local CSV file.
For more info, see:
mlflow pyfunc --help mlflow pyfunc serve --help mlflow pyfunc predict --help
mlflow.azureml module can export
python_function models as Azure ML compatible models. It
can also be used to directly deploy and serve models on Azure ML, provided the environment has
been correctly set up.
exportexports the model in Azure ML-compatible format. MLflow will output a directory with the dependencies necessary to deploy the model.
deploydeploys the model directly to Azure ML. You first need to set up your environment to work with the Azure ML CLI. You can do this by starting a shell from the Azure ML Workbench application. You also have to set up all accounts required to run and deploy on Azure ML. Where the model is deployed is dependent on your active Azure ML environment. If the active environment is set up for local deployment, the model will be deployed locally in a Docker container (Docker is required).
Model export example:
mlflow azureml export -m <path-to-model> -o test-output tree test-output
test-output ├── create_service.sh - use this script to upload the model to Azure ML ├── score.py - main module required by Azure ML └── test-output - directory containing MLflow model in Python Function flavor
Example workflow using the MLflow CLI
az ml set env <local-env> - set environment to local deployment mlflow azureml deploy <parameters> - deploy locally to test the model az ml set env <cluster-env> - set environment to cluster mlflow azureml deploy <parameters> - deploy to the cloud
For more info, see:
mlflow azureml --help mlflow azureml export --help mlflow azureml deploy --help
mlflow.sagemaker module can deploy
python_function models on SageMaker
or locally in a Docker container with SageMaker compatible environment.
You have to set up your environment and user accounts first in order to
deploy to SageMaker with MLflow. Also, in order to export a custom model to SageMaker, you need a
MLflow-compatible Docker image to be available on Amazon ECR. MLflow provides a default Docker
image definition; however, it is up to you to build the actual image and upload it to ECR.
MLflow includes a utility function to perform this step. Once built and uploaded, the MLflow
container can be used for all MLflow models.
build-and-push-containerCLI command builds an MLfLow Docker image and uploads it to ECR. The caller must have the correct permissions set up. The image is built locally and requires Docker to be present on the machine that performs this step.
run-localdeploys the model locally in a Docker container. The image and the environment should be identical to how the model would be run remotely and it is therefore useful for testing the model prior to deployment.
deploydeploys the model on Amazon SageMaker. MLflow uploads the Python Function model into S3 and starts an Amazon SageMaker endpoint serving the model.
Example workflow using the MLflow CLI
mlflow sagemaker build-and-push-container - build the container (only needs to be called once) mlflow sagemaker run-local -m <path-to-model> - test the model locally mlflow sagemaker deploy <parameters> - deploy the model to the cloud
For more info, see:
mlflow sagemaker --help mlflow sagemaker build-and-push-container --help mlflow sagemaker run-local --help mlflow sagemaker deploy --help