Build Your Own Container with Multi Model Server

Custom Elastic Container Registry (ECR) images deployed in Amazon SageMaker are expected to adhere to the basic contract described in Use Your Own Inference Code with Hosting Services that govern how Amazon SageMaker interacts with a Docker container that runs your own inference code. For a container to be capable of loading and serving multiple models concurrently, there are additional APIs and behaviors that must be followed. This additional contract includes new APIs to load, list, get, and unload models, and a different API to invoke models. There are also different behaviors for error scenarios that the APIs need to abide by. To indicate that the container complies with the additional requirements, you can add the following command to your Docker file:

LABEL com.amazonaws.sagemaker.capabilities.multi-models=true

Amazon SageMaker also injects an environment variable into the container

SAGEMAKER_MULTI_MODEL=true

If you are creating a multi-model endpoint for a serial inference pipline, your Docker file must have the required labels for both multi-models and serial inference pipelines. For more information about serial information pipelines, see Run Real-time Predictions with an Inference Pipeline.

To help you implement these requirements for a custom container, two libraries are available:

• Multi Model Server is an open source framework for serving machine learning models that can be installed in containers to provide the front end that fulfills the requirements for the new multi-model endpoint container APIs. It provides the HTTP front end and model management capabilities required by multi-model endpoints to host multiple models within a single container, load models into and unload models out of the container dynamically, and performs inference on a specified loaded model. It also provides a pluggable backend that supports a pluggable custom backend handler where you can implement your own algorithm.

• Amazon SageMaker Inference Toolkit is a library that bootstraps Multi Model Server with a configuration and settings that make it compatible with Amazon SageMaker multi-model endpoints. It also allows you to tweak important performance parameters, such as the number of workers per model, depending on the needs of your scenario.

Use the Amazon SageMaker Inference Toolkit

Currently, the only pre-built containers that support multi-model endpoints are the MXNet inference container an the PyTorch inference container. If you want to use any other framework or algorithm, you need to build a container. The easiest way to do this is to use the Amazon SageMaker Inference Toolkit to extend an existing pre-built container. The Amazon SageMaker inference toolkit is an implementation for the multi-model server (MMS) that creates endpoints that can be deployed in Amazon SageMaker. For a sample notebook that shows how to set up and deploy a custom container that supports multi-model endpoints in Amazon SageMaker, see the Multi-Model Endpoint BYOC Sample Notebook.

Note

The Amazon SageMaker inference toolkit supports only Python model handlers. If you want to implement your handler in any other language, you must build your own container that implements the additional multi-model endpoint APIs. For information, see Contract for Custom Containers to Serve Multiple Model.

To extend a container by using the Amazon SageMaker inference toolkit

1. Create a model handler. MMS expects a model handler, which is a Python file that implements functions to pre-process, get preditions from the model, and process the output in a model handler. For an example of a model handler, see model_handler.py from the sample notebook.

2. Import the inference toolkit and use its model_server.start_model_server function to start MMS. The following example is from the dockerd-entrypoint.py file from the sample notebook. Notice that the call to model_server.start_model_server passes the model handler described in the previous step:

   import subprocess
   import sys
   import shlex
   import os
   from retrying import retry
   from subprocess import CalledProcessError
   from sagemaker_inference import model_server
   
   def _retry_if_error(exception):
       return isinstance(exception, CalledProcessError or OSError)
   
   @retry(stop_max_delay=1000 * 50,
          retry_on_exception=_retry_if_error)
   def _start_mms():
       # by default the number of workers per model is 1, but we can configure it through the
       # environment variable below if desired.
       # os.environ['SAGEMAKER_MODEL_SERVER_WORKERS'] = '2'
       model_server.start_model_server(handler_service='/home/model-server/model_handler.py:handle')
   
   def main():
       if sys.argv[1] == 'serve':
           _start_mms()
       else:
           subprocess.check_call(shlex.split(' '.join(sys.argv[1:])))
   
       # prevent docker exit
       subprocess.call(['tail', '-f', '/dev/null'])
       
   main()

3. In your Dockerfile, copy the model handler from the first step and specify the Python file from the previous step as the entrypoint in your Dockerfile. The following lines are from the Dockerfile used in the sample notebook:

   # Copy the default custom service file to handle incoming data and inference requests
   COPY model_handler.py /home/model-server/model_handler.py
   
   # Define an entrypoint script for the docker image
   ENTRYPOINT ["python", "/usr/local/bin/dockerd-entrypoint.py"]

4. Build and register your container. The following shell script from the sample notebook builds the container and uploads it to an Amazon Elastic Container Registry repository in your AWS account:

   %%sh
   
   # The name of our algorithm
   algorithm_name=demo-sagemaker-multimodel
   
   cd container
   
   account=$(aws sts get-caller-identity --query Account --output text)
   
   # Get the region defined in the current configuration (default to us-west-2 if none defined)
   region=$(aws configure get region)
   region=${region:-us-west-2}
   
   fullname="${account}.dkr.ecr.${region}.amazonaws.com/${algorithm_name}:latest"
   
   # If the repository doesn't exist in ECR, create it.
   aws ecr describe-repositories --repository-names "${algorithm_name}" > /dev/null 2>&1
   
   if [ $? -ne 0 ]
   then
       aws ecr create-repository --repository-name "${algorithm_name}" > /dev/null
   fi
   
   # Get the login command from ECR and execute it directly
   $(aws ecr get-login --region ${region} --no-include-email)
   
   # Build the docker image locally with the image name and then push it to ECR
   # with the full name.
   
   docker build -q -t ${algorithm_name} .
   docker tag ${algorithm_name} ${fullname}
   
   docker push ${fullname}

You can now use this container to deploy multi-model endpoints in Amazon SageMaker.

Topics

• Contract for Custom Containers to Serve Multiple Model