KServe

MLServer is used as the core Python inference server in KServe (formerly known as KFServing). This allows for a straightforward avenue to deploy your models into a scalable serving infrastructure backed by Kubernetes.

This section assumes a basic knowledge of KServe and Kubernetes, as well as access to a working Kubernetes cluster with KServe installed. To learn more about KServe or how to install it, please visit the KServe documentation.

Serving Runtimes

KServe provides built-in serving runtimes to deploy models trained in common ML frameworks. These allow you to deploy your models into a robust infrastructure by just pointing to where the model artifacts are stored remotely.

Some of these runtimes leverage MLServer as the core inference server. Therefore, it should be straightforward to move from your local testing to your serving infrastructure.

Usage

To use any of the built-in serving runtimes offered by KServe, it should be enough to select the relevant one your InferenceService manifest.

For example, to serve a Scikit-Learn model, you could use a manifest like the one below:

apiVersion: serving.kserve.io/v1beta1
kind: InferenceService
metadata:
  name: my-model
spec:
  predictor:
    sklearn:
      protocolVersion: v2
      storageUri: gs://seldon-models/sklearn/iris

As you can see highlighted above, the InferenceService manifest will only need to specify the following points:

• The model artifact is a Scikit-Learn model. Therefore, we will use the sklearn serving runtime to deploy it.

• The model will be served using the V2 inference protocol, which can be enabled by setting the protocolVersion field to v2.

Once you have your InferenceService manifest ready, then the next step is to apply it to your cluster. There are multiple ways to do this, but the simplest is probably to just apply it directly through kubectl, by running:

kubectl apply -f my-inferenceservice-manifest.yaml

Supported Serving Runtimes

As mentioned above, KServe offers support for built-in serving runtimes, some of which leverage MLServer as the inference server. Below you can find a table listing these runtimes, and the MLServer inference runtime that they correspond to.

Framework	MLServer Runtime	KServe Serving Runtime	Documentation
Scikit-Learn	MLServer SKLearn	sklearn	SKLearn Serving Runtime
XGBoost	MLServer XGBoost	xgboost	XGBoost Serving Runtime

Note that, on top of the ones shown above (backed by MLServer), KServe also provides a wider set of serving runtimes. To see the full list, please visit the KServe documentation.

Custom Runtimes

Sometimes, the serving runtimes built into KServe may not be enough for our use case. The framework provided by MLServer makes it easy to write custom runtimes, which can then get packaged up as images. These images then become self-contained model servers with your custom runtime. Therefore, it's easy to deploy them into your serving infrastructure leveraging KServe support for custom runtimes.

Usage

The InferenceService manifest gives you full control over the containers used to deploy your machine learning model. This can be leveraged to point your deployment to the custom MLServer image containing your custom logic. For example, if we assume that our custom image has been tagged as my-custom-server:0.1.0, we could write an InferenceService manifest like the one below:

apiVersion: serving.kserve.io/v1beta1
kind: InferenceService
metadata:
  name: my-model
spec:
  predictor:
    containers:
      - name: classifier
        image: my-custom-server:0.1.0
        env:
          - name: PROTOCOL
            value: v2
        ports:
          - containerPort: 8080
            protocol: TCP

As we can see highlighted above, the main points that we'll need to take into account are:

• Pointing to our custom MLServer image in the custom container section of our InferenceService.

• Explicitly choosing the V2 inference protocol to serve our model.

• Let KServe know what port will be exposed by our custom container to send inference requests.

Once you have your InferenceService manifest ready, then the next step is to apply it to your cluster. There are multiple ways to do this, but the simplest is probably to just apply it directly through kubectl, by running:

kubectl apply -f my-inferenceservice-manifest.yaml