Packaging a Java model for Seldon Core using s2i

In this guide, we illustrate the steps needed to wrap your own Java model in a docker image ready for deployment with Seldon Core using source-to-image app s2i.

If you are not familiar with s2i you can read general instructions on using s2i and then follow the steps below.

Step 1 - Install s2i

  • Prerequisites for using s2i are:

    • Docker

    • Git (if building from a remote git repo)

To check everything is working you can run

s2i usage seldonio/seldon-core-s2i-java-build:0.1

Step 2 - Create your source code

To use our s2i builder image to package your Java model you will need:

  • A Maven project that depends on io.seldon.wrapper library

  • A Spring Boot configuration class

  • A class that implements io.seldon.wrapper.api.SeldonPredictionService for the type of component you are creating

  • .s2i/environment - model definitions used by the s2i builder to correctly wrap your model

We will go into detail for each of these steps:

Maven Project

Create a Spring Boot Maven project and include the dependency:


A full example can be found at incubating/wrappers/s2i/java/test/model-template-app/pom.xml.

Spring Boot Intialization

Create a main App class:

  • Add @EnableAsync annotation (to allow the embedded gRPC server to start at Spring Boot startup)

  • include the io.seldon.wrapper in the scan base packages list along with your App’s package, in the example below the Apps’s package is io.seldon.example.

  • Import the config class at io.seldon.wrapper.config.AppConfig.class

For example:

@SpringBootApplication(scanBasePackages = {"io.seldon.wrapper","io.seldon.example"})
@Import({ io.seldon.wrapper.config.AppConfig.class })
public class App {
    public static void main(String[] args) throws Exception {
  , args);

Prediction Class

To handle requests to your model or other component you need to implement one or more of the methods in io.seldon.wrapper.api.SeldonPredictionService, in particular:

default public SeldonMessage predict(SeldonMessage request);
default public SeldonMessage route(SeldonMessage request);
default public SeldonMessage sendFeedback(Feedback request);
default public SeldonMessage transformInput(SeldonMessage request);
default public SeldonMessage transformOutput(SeldonMessage request);
default public SeldonMessage aggregate(SeldonMessageList request);

Your implementing class should be created as a Spring Component so it will be managed by Spring. There is a full H2O example in examples/models/h2o_mojo/src/main/java/io/seldon/example/h2o/model, whose implementation is shown below:

public class H2OModelHandler implements SeldonPredictionService {
    private static Logger logger = LoggerFactory.getLogger(H2OModelHandler.class.getName());
    EasyPredictModelWrapper model;

    public H2OModelHandler() throws IOException {
        MojoReaderBackend reader =
        MojoModel modelMojo = ModelMojoReader.readFrom(reader);
        model = new EasyPredictModelWrapper(modelMojo);"Loaded model");

    public SeldonMessage predict(SeldonMessage payload) {
        List<RowData> rows = H2OUtils.convertSeldonMessage(payload.getData());
        List<AbstractPrediction> predictions = new ArrayList<>();
        for(RowData row : rows)
                BinomialModelPrediction p = model.predictBinomial(row);
            } catch (PredictException e) {
      "Error in prediction ",e);
        DefaultData res = H2OUtils.convertH2OPrediction(predictions, payload.getData());

        return SeldonMessage.newBuilder().setData(res).build();


The above code:

  • loads a model from the local resources folder on startup

  • Converts the proto buffer message into H2O RowData using provided utility classes.

  • Runs a BionomialModel prediction and converts the result back into a SeldonMessage for return

H2O Helper Classes

We provide H2O utility class io.seldon.wrapper.utils.H2OUtils in seldon-core-wrapper to convert to and from the seldon-core proto buffer message types.

DL4J Helper Classes

We provide a DL4J utility class io.seldon.wrapper.utils.DL4JUtils in seldon-core-wrapper to convert to and from the seldon-core proto buffer message types.


Define the core parameters needed by our R builder image to wrap your model. An example is:


These values can also be provided or overridden on the command line when building the image.

Step 3 - Build your image

Use s2i build to create your Docker image from source code. You will need Docker installed on the machine and optionally git if your source code is in a public git repo.

Using s2i you can build directly from a git repo or from a local source folder. See the s2i docs for further details. The general format is:

s2i build <git-repo> seldonio/seldon-core-s2i-java-build:0.1 <my-image-name> --runtime-image seldonio/seldon-core-s2i-java-runtime:0.1
s2i build <src-folder> seldonio/seldon-core-s2i-java-build:0.1 <my-image-name> --runtime-image seldonio/seldon-core-s2i-java-runtime:0.1

An example invocation using the test template model inside seldon-core:

s2i build --context-dir=incubating/wrappers/s2i/java/test/model-template-app seldonio/seldon-core-s2i-java-build:0.1 h2o-test:0.1 --runtime-image seldonio/seldon-core-s2i-java-runtime:0.1

The above s2i build invocation:

  • uses the GitHub repo: and the directory incubating/wrappers/s2i/java/test/model-template-app inside that repo.

  • uses the builder image seldonio/seldon-core-s2i-java-build

  • uses the runtime image seldonio/seldon-core-s2i-java-runtime

  • creates a docker image seldon-core-template-model

For building from a local source folder, an example where we clone the seldon-core repo:

git clone
cd seldon-core
s2i build incubating/wrappers/s2i/java/test/model-template-app seldonio/seldon-core-s2i-java-build:0.1 h2o-test:0.1 --runtime-image seldonio/seldon-core-s2i-java-runtime:0.1

For more help see:

s2i usage seldonio/seldon-core-s2i-java-build:0.1
s2i build --help


Environment Variables

The required environment variables understood by the builder image are explained below. You can provide them in the .s2i/environment file or on the s2i build command line.


API type to create. Can be REST or GRPC.


The service type being created. Available options are:





Creating different service types