image-classification-tensorflow

Data processing Model training Deploying and smoke testing

Overview

Demonstrates how to use Azure DevOps and Azure ML to build, train, evaluate, and track models, including how to retrain on new data based on the Tensorflow Image Classification sample.

What does this sample demonstrate:

• Track ML experimentation and model performance in Azure ML, and trace back to the source code build version and training dataset version.
• Manage dependencies in CI/CD, training, inferencing, and local development for an image classification model based on Tensorflow and Keras.
• Use Azure ML input/output file datasets when training on image data.
• Manage datasets and retrain on new data.

What doesn't this sample demonstrate:

• Comprehensive unit and integration tests - this sample doesn't have the level of unit tests or integration tests adequate for production deployment yet. Refer to this sample to learn how to mock Azure ML SDK and build a rich set of tests.
• Production scale inferencing - this sample stops at deploying the model to Azure Container Instance for smoke testing.

Model Tracking

An ML model comes from a training experiment which consists of multiple runs. In this sample, each run is an Azure ML pipeline run which also consists of multiple steps or child runs. The goal is to track the following lineage as well as the input parameters to and output metrics from model training.

model -> experiment -> pipeline run -> step runs -> datasets and devops build

Dependency Management

This solution takes dependencies on Python libraries, Azure ML SDK, Tensorflow and Keras packages. It also relies on Azure Cli, Azure ML extension for Azure Cli, and PyTest etc dependng on what needs to run and where. Dependencies are managed as following:

1. Packages required for ML training are defined in ml_model/conda_dependencies.yml. When training in Azure, Azure ML creates a docker image based on this file.
2. For Azure DevOps pipelines to run unit tests, the build agent must also have the dependent packages installed. This is defined in devops_pipelines/build_agent/ci_dependencies.yml. The ML related dependencies are same as ml_model/conda_dependencies.yml. However, it also needs linting and testing frameworks. The build agent pipeline then builds this conda environment into a Docker image to run for all pipelines.
3. When running locally on the dev machine, you can either use a VSCode dev container or a conda environment. Dev dependencies is similar to build agent dependencies, except you may also want to install Jupyter notebook or debugger. Dev dependencies is defined in local_development/dev_dependencies.yml. The dev container create a conda environment based on this file, or you can simply create a conda environment on the dev machine without a container.

We use the same ML dependencies for running all ML operations in Azure ML. In reality, preprocessing or inferencing don't always need all the packages used in model training. Similarly, not all Azure DevOps pipelines require the same dependencies in the build agent. You can create different Docker images with minimum required dependencies to keep the image size small, with the tradeoff of having to manage more images.

Dataset Management

When preprocessing images, such as normalizing and resizing, the output of the processed data needs to be registered as a dataset so that models can be trained on such datasets and tracked. Also, we don't want to preprocess the data over and over just because we need to train the models over and over to get the best results. This means:

• Preprocessing and training should be in separate pipelines.
• Datasets are immutable when you mount them. How do you write a new output dataset for the processed images? You can of course use Azure Blob Storage SDK to write files to blob storage, and then use Azure ML SDK to create new datasets. But since we are already using Azure ML pipeline to produce the data, using OutputFileDatasetConfig makes it easier to register a dataset as data is produced in an Azure ML pipeline.

Retrain on New Data

When new data arrives, there's no code change, so retraining the model should happen in the ML pipelines not DevOps pipelines. Additionally the newly trained model should be able to trace back to the new data it's trained on. This means:

• Datasets should be immutable.
• Training dataset or dataset version can't be determined at pipeline publishing time, it has to be passed in as parameters at pipeline runtime. To train on new data, put new data in a new folder. The data processing pipeline uses a pre-registered dataset name. It also takes a folder name as its parameter. When a new folder is specified for a run, a new version of the dataset is registered and the folder is mounted. When this parameter is nopath, the latest version of the dataset is used for training.

Getting Started

Prerequisite

1. Whether you run this project locally or in Azure DevOps CI/CD pipelines, the code needs to get Azure ML context for remote or offline runs. Create Azure resources as documented here.
2. Review the folder structure explained here.

Running locally

1. Make a copy of .env.example, place it in the root of this sample, configure the variables, and rename the file to .env.

2. Install Anaconda or Mini Conda and create a Conda envrionment by running local_install_requirements.sh.

3. In VSCode, open the root folder of this sample, select the Conda environment created above as the Python interpretor.

4. Most of the code you'd want to run locally is in ml_model folder. For code that doesn't depend on Azure ML, for example, preprocess_images.py, you can debug as usual. For code that depends on Azure ML, you don't have access to Azure ML resources such as Datasets. You'll need to write different code for local vs. remote runs. For example, to debug preprocess_aml.py, do the following:

   • Open a terminal, activate the Conda environment for this sample, nativate to the root folder of this sample, and run pytest.

   • In the terminal, navigate to ml_model folder of this sample, and run:

   image-classification-tensorflow/ml_model$ python -m debugpy --listen 5678 --wait-for-client preprocess/preprocess_aml.py --dataset_name flower_dataset --data_file_path /path/to/local/raw/images --output_dataset /path/to/processed/images

   • In VSCode, create a launch configuration to attach to the debugger, and F5:

   "configurations": [
     {
       "name": "Python: Attach",
       "cwd": "${workspaceFolder}/samples/image-classification-tensorflow/ml_model",
       "type": "python",
       "request": "attach",
       "connect": {
         "host": "localhost",
         "port": 5678
       },
     }
   ]

CI/CD in Azure DevOps

1. Create an Azure DevOps variable group devopsforai-aml-vg that contains the following variables:

name	description
ACR_SVC_CONNECTION	Service Connection to a Docker Container Registry to store and retrieve the Docker container for build agent
AML_COMPUTE_CLUSTER_NAME	Azure ML Compute cluster used for training
RESOURCE_GROUP	Azure Resource Group where the Azure ML Workspace is located
WORKSPACE_NAME	Azure ML Workspace name
WORKSPACE_SVC_CONNECTION	Service Connection to Azure ML Workspace
ACI_DEPLOYMENT_NAME	Azure ML deployment name to Azure Container Instance
TEST_IMAGE_CLASSES	a comma separated list of image classification class names of images for smoke testing
TEST_IMAGE_URLS	a comma separated URLs of images for smoke testing

Note that you can also overwrite the variables defined in variables-template.yml with the ones defined in this variable group. Variables defined in the variable group takes precedence over variables-template.yml because of the order they are defined in Azure DevOps pipelines.

2. Create the build agent

The build agent needs to run linting, unit tests, and call Azure ML SDK to publish Azure ML pipelines so that models can be trained, evaluated, and deployed in Azure ML pipelines. To create a Docker image for the build agent, create and run a build pipeline with 00-build-agent-pipeline.yml.

3. Create other pipelines

Create the remaining CI/CD pipelines defined in devops_pipelines folder. Verify or adjust their triggers if needed. By default, only linting and unit tests are triggered for pull request validation. Data processing and model training are only triggered on merging to main.