Tutorial

This tutorial showcases how you can use MLflow end-to-end to:

  • Train a linear regression model
  • Package the code that trains the model in a reusable and reproducible model format
  • Deploy the model into a simple HTTP server that will enable you to score predictions

This tutorial uses a dataset to predict the quality of wine based on quantitative features like the wine’s “fixed acidity”, “pH”, “residual sugar”, and so on. The dataset is from UCI’s machine learning repository. [1]

What You’ll Need

This tutorial uses MLflow, conda, and the tutorial code located at example/tutorial in the MLflow repository. To download the tutorial code, run:

git clone https://github.com/databricks/mlflow

Training the Model

First, train a linear regression model that takes two hyperparameters: alpha and l1_ratio. The code is located at example/tutorial/train.py and is reproduced below.

import os
import sys

import pandas as pd
import numpy as np
from sklearn.metrics import mean_squared_error, mean_absolute_error, r2_score
from sklearn.model_selection import train_test_split
from sklearn.linear_model import ElasticNet

import mlflow
import mlflow.sklearn
# Run from the root of MLflow
# Read the wine-quality csv file
wine_path = os.path.join(os.path.dirname(os.path.abspath(__file__)), "wine-quality.csv")
data = pd.read_csv(wine_path)

# Split the data into training and test sets. (0.75, 0.25) split.
train, test = train_test_split(data)

# The predicted column is "quality" which is a scalar from [3, 9]
train_x = train.drop(["quality"], axis=1)
test_x = test.drop(["quality"], axis=1)
train_y = train[["quality"]]
test_y = test[["quality"]]

alpha = float(sys.argv[1]) if len(sys.argv) > 1 else 0.5
l1_ratio = float(sys.argv[2]) if len(sys.argv) > 2 else 0.5

with mlflow.start_run():
    lr = ElasticNet(alpha=alpha, l1_ratio=l1_ratio, random_state=42)
    lr.fit(train_x, train_y)

    predicted_qualities = lr.predict(test_x)

    (rmse, mae, r2) = eval_metrics(test_y, predicted_qualities)

    print("Elasticnet model (alpha=%f, l1_ratio=%f):" % (alpha, l1_ratio))
    print("  RMSE: %s" % rmse)
    print("  MAE: %s" % mae)
    print("  R2: %s" % r2)

    mlflow.log_param("alpha", alpha)
    mlflow.log_param("l1_ratio", l1_ratio)
    mlflow.log_metric("rmse", rmse)
    mlflow.log_metric("r2", r2)
    mlflow.log_metric("mae", mae)

    mlflow.sklearn.log_model(lr, "model")

This example uses the familiar pandas, numpy, and sklearn APIs to create a simple machine learning model. The MLflow tracking APIs log information about each training run, like the hyperparameters alpha and l1_ratio, used to train the model and metrics, like the root mean square error, used to evaluate the model. The example also serializes the model in a format that MLflow knows how to deploy.

You can run the example with default hyperparameters as follows:

python example/tutorial/train.py

Try out some other values for alpha and l1_ratio by passing them as arguments to train.py:

python example/tutorial/train.py <alpha> <l1_ratio>

Each time you run the example, MLflow logs information about your experiment runs in the directory mlruns.

Note

If you would like to use the Jupyter notebook version of train.py, try out the tutorial notebook at example/tutorial/train.py/train.ipynb.

Comparing the Models

Next, use the MLflow UI to compare the models that you have produced. Run mlflow ui in the same current working directory as the one that contains the mlruns directory and open http://localhost:5000 in your browser.

On this page, you can see a list of experiment runs with metrics you can use to compare the models.

_images/tutorial-compare.png

You can see that the lower alpha is, the better the model. You can also use the search feature to quickly filter out many models. For example, the query metrics.rmse < 0.8 returns all the models with root mean squared error less than 0.8. For more complex manipulations, you can download this table as a CSV and use your favorite data munging software to analyze it.

Packaging the Training Code

Now that you have your training code, you can package it so that other data scientists can easily reuse the model, or so that you can run the training remotely, for example on Databricks. You do this by using MLflow Projects conventions to specify the dependencies and entry points to your code. The example/tutorial/MLproject file specifies that the project has the dependencies located in a Conda environment file called conda.yaml and has one entry point that takes two parameters: alpha and l1_ratio.

# example/tutorial/MLproject

name: tutorial

conda_env: conda.yaml

entry_points:
  main:
    parameters:
      alpha: float
      l1_ratio: {type: float, default: 0.1}
    command: "python train.py {alpha} {l1_ratio}"

The Conda file lists the dependencies:

# example/tutorial/conda.yaml

name: tutorial
channels:
  - defaults
dependencies:
  - numpy=1.14.3
  - pandas=0.22.0
  - scikit-learn=0.19.1
  - pip:
    - mlflow

To run this project, invoke mlflow run example/tutorial -P alpha=0.42. After running this command, MLflow will run your training code in a new Conda environment with the dependencies specified in conda.yaml.

If the repository has an MLproject file in the root you can also run a project directly from GitHub. This tutorial is duplicated in the https://github.com/databricks/mlflow-example repository which you can run with mlflow run git@github.com:databricks/mlflow-example.git -P alpha=0.42.

Serving the Model

Now that you have packaged your model using the MLproject convention and have identified the best model, it is time to deploy the model using MLflow Models. 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.

In the example training code, after training the linear regression model, a function in MLflow saved the model as an artifact within the run.

mlflow.sklearn.log_model(lr, "model")

To view this artifact, you can use the UI again. When you click a date in the list of experiment runs you’ll see this page.

_images/tutorial-artifact.png

At the bottom, you can see that the call to mlflow.sklearn.log_model produced two files in /Users/mlflow/mlflow-prototype/mlruns/0/7c1a0d5c42844dcdb8f5191146925174/artifacts/model. The first file, MLmodel, is a metadata file that tells MLflow how to load the model. The second file, model.pkl, is a serialized version of the linear regression model that you trained.

In this example, you can use this MLmodel format with MLflow to deploy a local REST server that can serve predictions.

To deploy the server, run:

mlflow sklearn serve /Users/mlflow/mlflow-prototype/mlruns/0/7c1a0d5c42844dcdb8f5191146925174/artifacts/model -p 1234

Note

The version of Python used to create the model must be the same as the one running mlflow sklearn. If this is not the case, you may see the error UnicodeDecodeError: 'ascii' codec can't decode byte 0x9f in position 1: ordinal not in range(128) or raise ValueError, "unsupported pickle protocol: %d".

To serve a prediction, run:

curl -X POST -H "Content-Type:application/json" --data '[{"fixed acidity": 6.2, "volatile acidity": 0.66, "citric acid": 0.48, "residual sugar": 1.2, "chlorides": 0.029, "free sulfur dioxide": 29, "total sulfur dioxide": 75, "density": 0.98, "pH": 3.33, "sulphates": 0.39, "alcohol": 12.8}]' http://127.0.0.1:1234/invocations

which should return something like:

{"predictions": [6.379428821398614]}

More Resources

Congratulations on finishing the tutorial! For more reading, see MLflow Tracking, MLflow Projects, MLflow Models, and more.

[1]
  1. Cortez, A. Cerdeira, F. Almeida, T. Matos and J. Reis. Modeling wine preferences by data mining from physicochemical properties. In Decision Support Systems, Elsevier, 47(4):547-553, 2009.