Using MicroStream persistence with Micronaut

Learn how to use MicroStream as a high-performance persistence layer.

Authors: Tim Yates

Micronaut Version: 4.6.3

1. Getting Started

In this guide, we will create a Micronaut application written in Java.

You will use MicroStream for persistence.

2. What you will need

To complete this guide, you will need the following:

Some time on your hands
A decent text editor or IDE (e.g. IntelliJ IDEA)
JDK 17 or greater installed with JAVA_HOME configured appropriately

3. Solution

We recommend that you follow the instructions in the next sections and create the application step by step. However, you can go right to the completed example.

Download and unzip the source

4. Writing the Application

Create an application using the Micronaut Command Line Interface or with Micronaut Launch.

mn create-app example.micronaut.micronautguide \
    --features=yaml,microstream,serialization-jackson,validation \
    --build=gradle \
    --lang=java \
    --test=junit

If you don’t specify the --build argument, Gradle with the Kotlin DSL is used as the build tool.
If you don’t specify the --lang argument, Java is used as the language.
If you don’t specify the --test argument, JUnit is used for Java and Kotlin, and Spock is used for Groovy.

The previous command creates a Micronaut application with the default package example.micronaut in a directory named micronautguide.

If you use Micronaut Launch, select Micronaut Application as application type and add yaml, microstream, serialization-jackson, and validation features.

If you have an existing Micronaut application and want to add the functionality described here, you can view the dependency and configuration changes from the specified features, and apply those changes to your application.

Diff

Setup IntelliJ IDEA to develop Micronaut Applications.

4.1. Dependencies

The microstream features adds the following dependencies:

build.gradle

annotationProcessor("io.micronaut.microstream:micronaut-microstream-annotations")
implementation("io.micronaut.microstream:micronaut-microstream-annotations")
implementation("io.micronaut.microstream:micronaut-microstream")

4.2. Domain object

Create a Fruit class which will be used as the domain object.

src/main/java/example/micronaut/Fruit.java

package example.micronaut;

import io.micronaut.core.annotation.NonNull;
import io.micronaut.core.annotation.Nullable;
import io.micronaut.serde.annotation.Serdeable;

import jakarta.validation.constraints.NotBlank;

@Serdeable (1)
public class Fruit {

    @NonNull
    @NotBlank (2)
    private final String name;

    @Nullable (3)
    private String description;

    public Fruit(@NonNull String name,
                 @Nullable String description) {
        this.name = name;
        this.description = description;
    }

    @NonNull
    public String getName() {
        return name;
    }

    @Nullable
    public String getDescription() {
        return description;
    }

    public void setDescription(@Nullable String description) {
        this.description = description;
    }
}

1	Declare the `@Serdeable` annotation at the type level in your source code to allow the type to be serialized or deserialized.
2	Use `jakarta.validation.constraints` Constraints to ensure the data matches your expectations.
3	The description is allowed to be null.

4.3. Root Object

Create a FruitContainer POJO which we will be used as the root of our object graph.

src/main/java/example/micronaut/FruitContainer.java

package example.micronaut;

import io.micronaut.core.annotation.NonNull;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

public class FruitContainer {

    @NonNull
    private final Map<String, Fruit> fruits = new ConcurrentHashMap<>();

    @NonNull
    public Map<String, Fruit> getFruits() {
        return fruits;
    }
}

4.4. Configuration

Add the following snippet to application.yml to configure MicroStream.

Since Micronaut Framework 4.0, to use YAML configuration, you have to add the YAML dependency.

src/main/resources/application.yml

microstream:
  storage:
    main:
      root-class: 'example.micronaut.FruitContainer'
      storage-directory: 'build/fruit-storage'

4.5. Command object

And a FruitCommand class which will be used as the command object over HTTP.

src/main/java/example/micronaut/FruitCommand.java

package example.micronaut;

import io.micronaut.core.annotation.Creator;
import io.micronaut.core.annotation.NonNull;
import io.micronaut.core.annotation.Nullable;
import io.micronaut.serde.annotation.Serdeable;

import jakarta.validation.constraints.NotBlank;

@Serdeable (1)
public class FruitCommand {

    @NonNull
    @NotBlank (2)
    private final String name;

    @Nullable (3)
    private final String description;

    public FruitCommand(@NonNull String name) {
        this(name, null);
    }

    @Creator
    public FruitCommand(@NonNull String name,
                        @Nullable String description) {
        this.name = name;
        this.description = description;
    }

    @NonNull
    public String getName() {
        return name;
    }

    @Nullable
    public String getDescription() {
        return description;
    }
}

1	Declare the `@Serdeable` annotation at the type level in your source code to allow the type to be serialized or deserialized.
2	Use `jakarta.validation.constraints` Constraints to ensure the data matches your expectations.
3	The description is allowed to be null.

4.6. Repository

Create a repository interface to encapsulate the CRUD actions for Fruit.

src/main/java/example/micronaut/FruitRepository.java

package example.micronaut;

import io.micronaut.core.annotation.NonNull;
import io.micronaut.core.annotation.Nullable;
import jakarta.validation.constraints.NotBlank;
import jakarta.validation.constraints.NotNull;
import java.util.Collection;
import jakarta.validation.Valid;

interface FruitRepository {

    @NonNull
    Collection<Fruit> list();

    @NonNull
    Fruit create(@NonNull @NotNull @Valid FruitCommand fruit) (1)
            throws FruitDuplicateException;

    @Nullable
    Fruit update(@NonNull @NotNull @Valid FruitCommand fruit); (1)

    @Nullable
    Fruit find(@NonNull @NotBlank String name);

    void delete(@NonNull @NotNull @Valid FruitCommand fruit); (1)
}

1	Add `@Valid` to any method parameter which requires validation.

4.7. Error handling

In the event an attempt is made to create a duplicate fruit, we will catch the exception with a custom class.

src/main/java/example/micronaut/FruitDuplicateException.java

package example.micronaut;

public class FruitDuplicateException extends RuntimeException{

    public FruitDuplicateException(String name) {
        super("Fruit '" + name + "' already exists.");
    }
}

This exception will be handled by a custom ExceptionHandler to return a 400 error with a sensible message.

src/main/java/example/micronaut/FruitDuplicateExceptionHandler.java

package example.micronaut;

import io.micronaut.http.HttpRequest;
import io.micronaut.http.HttpResponse;
import io.micronaut.http.annotation.Produces;
import io.micronaut.http.server.exceptions.ExceptionHandler;
import io.micronaut.http.server.exceptions.response.ErrorContext;
import io.micronaut.http.server.exceptions.response.ErrorResponseProcessor;
import jakarta.inject.Singleton;

@Produces (1)
@Singleton (2)
public class FruitDuplicateExceptionHandler implements ExceptionHandler<FruitDuplicateException, HttpResponse<?>> {

    private final ErrorResponseProcessor<?> errorResponseProcessor;

    public FruitDuplicateExceptionHandler(ErrorResponseProcessor<?> errorResponseProcessor) {
        this.errorResponseProcessor = errorResponseProcessor;
    }

    @Override
    public HttpResponse<?> handle(HttpRequest request, FruitDuplicateException exception) {
        ErrorContext errorContext = ErrorContext.builder(request)
                .cause(exception)
                .errorMessage(exception.getMessage())
                .build();
        return errorResponseProcessor.processResponse(errorContext, HttpResponse.unprocessableEntity());
    }
}

1	Ensure the response content-type is set to `application/json` with the `@Produces` annotation.
2	Use `jakarta.inject.Singleton` to designate a class as a singleton.

4.8. Repository implementation

Implement the FruitRepository interface.

When an object in your graph changes, you need to persist the object that contains the change. This can be achieved through the StoreParams and StoreReturn annotations

src/main/java/example/micronaut/FruitRepositoryImpl.java

package example.micronaut;

import io.micronaut.core.annotation.NonNull;
import io.micronaut.core.annotation.Nullable;
import io.micronaut.microstream.RootProvider;
import io.micronaut.microstream.annotations.StoreParams;
import io.micronaut.microstream.annotations.StoreReturn;
import jakarta.inject.Singleton;

import jakarta.validation.Valid;
import jakarta.validation.constraints.NotNull;
import jakarta.validation.constraints.NotBlank;
import java.util.Collection;
import java.util.Map;

@Singleton (1)
public class FruitRepositoryImpl implements FruitRepository {

    private final RootProvider<FruitContainer> rootProvider;

    FruitRepositoryImpl(RootProvider<FruitContainer> rootProvider) { (2)
        this.rootProvider = rootProvider;
    }

    @Override
    @NonNull
    public Collection<Fruit> list() {
        return rootProvider.root().getFruits().values(); (3)
    }

    @Override
    @NonNull
    public Fruit create(@NonNull @NotNull @Valid FruitCommand fruit) throws FruitDuplicateException {
        Map<String, Fruit> fruits = rootProvider.root().getFruits();
        if (fruits.containsKey(fruit.getName())) {
            throw new FruitDuplicateException(fruit.getName());
        }
        return performCreate(fruits, fruit);
    }

    @StoreParams("fruits") (4)
    protected Fruit performCreate(Map<String, Fruit> fruits, FruitCommand fruit) {
        Fruit newFruit = new Fruit(fruit.getName(), fruit.getDescription());
        fruits.put(fruit.getName(), newFruit);
        return newFruit;
    }

    @Nullable
    public Fruit update(@NonNull @NotNull @Valid FruitCommand fruit) {
        Map<String, Fruit> fruits = rootProvider.root().getFruits();
        Fruit foundFruit = fruits.get(fruit.getName());
        if (foundFruit != null) {
            return performUpdate(foundFruit, fruit);
        }
        return null;
    }

    @StoreReturn (5)
    protected Fruit performUpdate(@NonNull Fruit foundFruit, @NonNull FruitCommand fruit) {
        foundFruit.setDescription(fruit.getDescription());
        return foundFruit;
    }

    @Override
    @Nullable
    public Fruit find(@NonNull @NotBlank String name) {
        return rootProvider.root().getFruits().get(name);
    }

    @Override
    public void delete(@NonNull @NotNull @Valid FruitCommand fruit) {
        performDelete(fruit);
    }

    @StoreReturn (5)
    protected Map<String, Fruit> performDelete(FruitCommand fruit) {
        if (rootProvider.root().getFruits().remove(fruit.getName()) != null) {
            return rootProvider.root().getFruits();
        }
        return null;
    }
}

1	Use `jakarta.inject.Singleton` to designate a class as a singleton.
2	Use constructor injection to inject a bean of type `RootProvider`.
3	Return all the values in the `FruitContainer`.
4	With `@StoreParams`, on successful completion of this method, the Map argument `fruits` will be persisted in MicroStream.
5	With `@StoreReturn`, on successful completion of this method, the return value will be persisted in MicroStream.

4.9. Controller

Create FruitController:

src/main/java/example/micronaut/FruitController.java

package example.micronaut;

import io.micronaut.core.annotation.NonNull;
import io.micronaut.http.HttpStatus;
import io.micronaut.http.annotation.Body;
import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Delete;
import io.micronaut.http.annotation.Get;
import io.micronaut.http.annotation.PathVariable;
import io.micronaut.http.annotation.Post;
import io.micronaut.http.annotation.Put;
import io.micronaut.http.annotation.Status;
import io.micronaut.scheduling.annotation.ExecuteOn;

import jakarta.validation.Valid;
import jakarta.validation.constraints.NotNull;
import java.util.Collection;

import static io.micronaut.scheduling.TaskExecutors.BLOCKING;

@Controller("/fruits") (1)
class FruitController {

    private final FruitRepository fruitRepository;

    FruitController(FruitRepository fruitRepository) {  (2)
        this.fruitRepository = fruitRepository;
    }

    @Get (3)
    Collection<Fruit> list() {
        return fruitRepository.list();
    }

    @ExecuteOn(BLOCKING)
    @Post (4)
    @Status(HttpStatus.CREATED) (5)
    Fruit create(@NonNull @NotNull @Valid @Body FruitCommand fruit) { (6)
        return fruitRepository.create(fruit);
    }

    @Put
    Fruit update(@NonNull @NotNull @Valid @Body FruitCommand fruit) {
        return fruitRepository.update(fruit);
    }

    @Get("/{name}") (7)
    Fruit find(@PathVariable String name) {
        return fruitRepository.find(name);
    }

    @ExecuteOn(BLOCKING)
    @Delete
    @Status(HttpStatus.NO_CONTENT)
    void delete(@NonNull @Valid @Body FruitCommand fruit) {
        fruitRepository.delete(fruit);
    }
}

1	The class is defined as a controller with the @Controller annotation mapped to the path `/fruits`.
2	Use constructor injection to inject a bean of type `FruitRepository`.
3	The @Get annotation maps the `list` method to an HTTP GET request on `/fruits`.
4	The @Post annotation maps the `save` method to an HTTP POST request on `/fruits`.
5	You can specify the HTTP status code via the `@Status` annotation.
6	Add `@Valid` to any method parameter which requires validation.
7	The @Get annotation maps the `find` method to an HTTP GET request on `/fruits/{name}`.

4.10. Test

Create a test that verifies the validation of the FruitCommand POJO when we invoke the FruitRepository interface:

src/test/java/example/micronaut/FruitRepositoryTest.java

package example.micronaut;

import io.micronaut.test.extensions.junit5.annotation.MicronautTest;
import jakarta.inject.Inject;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.TestInstance;
import org.junit.jupiter.api.function.Executable;
import jakarta.validation.ConstraintViolationException;
import static org.junit.jupiter.api.Assertions.assertThrows;

@MicronautTest(startApplication = false) (1)
class FruitRepositoryTest {

    @Inject
    FruitRepository fruitRepository;

    @Test
    void methodsValidateParamers() {
        Executable e = () -> fruitRepository.create(new FruitCommand(""));
        assertThrows(ConstraintViolationException.class, e);
    }
}

1 Annotate the class with @MicronautTest so the Micronaut framework will initialize the application context and the embedded server. By default, each @Test method will be wrapped in a transaction that will be rolled back when the test finishes. This behaviour is is changed by setting transaction to false.

Create a test that verifies the validation of the FruitCommand POJO when we create a new entity via POST:

src/test/java/example/micronaut/FruitValidationControllerTest.java

package example.micronaut;

import io.micronaut.http.HttpRequest;
import io.micronaut.http.HttpStatus;
import io.micronaut.http.client.HttpClient;
import io.micronaut.http.client.annotation.Client;
import io.micronaut.http.client.exceptions.HttpClientResponseException;
import io.micronaut.test.extensions.junit5.annotation.MicronautTest;
import jakarta.inject.Inject;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.TestInstance;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertThrows;

@MicronautTest (1)
class FruitValidationControllerTest {

    @Inject
    @Client("/")
    HttpClient httpClient; (2)

    @Test
    void fruitIsValidated() {
        HttpClientResponseException exception = assertThrows(
                HttpClientResponseException.class,
                () -> httpClient.toBlocking().exchange(HttpRequest.POST("/fruits", new FruitCommand("", "")))
        );

        assertEquals(HttpStatus.BAD_REQUEST, exception.getStatus());
    }
}

1	Annotate the class with `@MicronautTest` so the Micronaut framework will initialize the application context and the embedded server. More info.
2	Inject the `HttpClient` bean and point it to the embedded server.

We will use temporary directories to persist our data under test.

To facilitate this, create a base test class that handles the creation of a temporary folder, and configuring the application.

src/test/java/example/micronaut/BaseTest.java

package example.micronaut;

import io.micronaut.test.support.TestPropertyProvider;
import org.junit.jupiter.api.io.TempDir;

import jakarta.validation.constraints.NotNull;
import java.io.File;
import java.util.Collections;
import java.util.Map;
import io.micronaut.core.annotation.NonNull;

abstract class BaseTest implements TestPropertyProvider {

    @TempDir
    static File tempDir;

    @Override
    @NonNull
    public Map<String, String> getProperties() {
        return Collections.singletonMap(
                "microstream.storage.main.storage-directory", tempDir.getAbsolutePath()
        );
    }
}

Create a test which validate FruitDuplicateExceptionHandler.

src/test/java/example/micronaut/FruitDuplicationExceptionHandlerTest.java

package example.micronaut;

import io.micronaut.http.HttpRequest;
import io.micronaut.http.HttpResponse;
import io.micronaut.http.HttpStatus;
import io.micronaut.http.client.HttpClient;
import io.micronaut.http.client.annotation.Client;
import io.micronaut.http.client.exceptions.HttpClientResponseException;
import io.micronaut.test.extensions.junit5.annotation.MicronautTest;
import jakarta.inject.Inject;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.TestInstance;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertThrows;

@MicronautTest (1)
@TestInstance(TestInstance.Lifecycle.PER_CLASS) (2)
class FruitDuplicationExceptionHandlerTest extends BaseTest {
    @Inject
    @Client("/")
    HttpClient httpClient; (3)

    @Test
    void duplicatedFruitsReturns400() {
        FruitCommand banana = new FruitCommand("Banana");
        HttpRequest<?> request = HttpRequest.POST("/fruits", banana);
        HttpResponse<?> response = httpClient.toBlocking().exchange(request);
        assertEquals(HttpStatus.CREATED, response.status());
        HttpClientResponseException exception = assertThrows(
                HttpClientResponseException.class,
                () -> httpClient.toBlocking().exchange(request)
        );
        assertEquals(HttpStatus.UNPROCESSABLE_ENTITY, exception.getStatus());
        HttpRequest<?> deleteRequest = HttpRequest.DELETE("/fruits", banana);
        HttpResponse<?> deleteResponse = httpClient.toBlocking().exchange(deleteRequest);
        assertEquals(HttpStatus.NO_CONTENT, deleteResponse.status());
    }
}

1	Annotate the class with `@MicronautTest` so the Micronaut framework will initialize the application context and the embedded server. More info.
2	Classes that implement `TestPropertyProvider` must use this annotation to create a single class instance for all tests (not necessary in Spock tests).
3	Inject the `HttpClient` bean and point it to the embedded server.

Add a Micronaut declarative HTTP Client to src/test to ease the testing of the application’s API.

src/test/java/example/micronaut/FruitClient.java

package example.micronaut;

import io.micronaut.core.annotation.NonNull;
import io.micronaut.http.HttpResponse;
import io.micronaut.http.HttpStatus;
import io.micronaut.http.annotation.Body;
import io.micronaut.http.annotation.Delete;
import io.micronaut.http.annotation.Get;
import io.micronaut.http.annotation.PathVariable;
import io.micronaut.http.annotation.Post;
import io.micronaut.http.annotation.Put;
import io.micronaut.http.client.annotation.Client;

import jakarta.validation.Valid;
import jakarta.validation.constraints.NotBlank;
import jakarta.validation.constraints.NotNull;
import java.util.Optional;

@Client("/fruits")
interface FruitClient {

    @Get
    Iterable<Fruit> list();

    @Get("/{name}")
    Optional<Fruit> find(@NonNull @NotBlank @PathVariable String name);

    @Post
    HttpResponse<Fruit> create(@NonNull @NotNull @Valid @Body FruitCommand fruit);

    @Put
    Optional<Fruit> update(@NonNull @NotNull @Valid @Body FruitCommand fruit);

    @NonNull
    @Delete
    HttpStatus delete(@NonNull @Valid @Body FruitCommand fruit);
}

And finally, create a test that checks our controller works against MicroStream correctly:

src/test/java/example/micronaut/FruitControllerTest.java

package example.micronaut;

import io.micronaut.context.ApplicationContext;
import io.micronaut.http.HttpResponse;
import io.micronaut.http.HttpStatus;
import io.micronaut.runtime.server.EmbeddedServer;
import org.junit.jupiter.api.Test;

import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;

import static org.junit.jupiter.api.Assertions.*;

class FruitControllerTest extends BaseTest {

    @Test
    void testInteractionWithTheController() {
        FruitCommand apple = new FruitCommand("apple", "Keeps the doctor away");
        String bananaName = "banana";
        String bananaDescription = "Yellow and curved";
        Map<String, Object> properties = new HashMap<>(getProperties());
        try (EmbeddedServer embeddedServer = ApplicationContext.run(EmbeddedServer.class, properties)) { (1)
            FruitClient fruitClient = embeddedServer.getApplicationContext().getBean(FruitClient.class);
            HttpResponse<Fruit> response = fruitClient.create(new FruitCommand(bananaName));
            assertEquals(HttpStatus.CREATED, response.getStatus());
            assertTrue(response.getBody().isPresent());
            Fruit banana = response.getBody().get();

            List<Fruit> fruitList = fruitsList(fruitClient);
            assertEquals(1, fruitList.size());
            assertEquals(banana.getName(), fruitList.get(0).getName());
            assertNull(fruitList.get(0).getDescription());

            Optional<Fruit> bananaOptional = fruitClient.update(apple);
            assertFalse(bananaOptional.isPresent());

            response = fruitClient.create(apple);
            assertEquals(HttpStatus.CREATED, response.getStatus());

            assertTrue(fruitsStream(fruitClient)
                    .anyMatch(f -> "Keeps the doctor away".equals(f.getDescription())));
            bananaOptional = fruitClient.update(new FruitCommand(bananaName, bananaDescription));
            assertTrue(bananaOptional.isPresent());
            assertEquals(
                    Stream.of("Keeps the doctor away", "Yellow and curved").collect(Collectors.toSet()),
                    fruitsStream(fruitClient)
                            .map(Fruit::getDescription)
                            .collect(Collectors.toSet())
            );
        }
        try (EmbeddedServer embeddedServer = ApplicationContext.run(EmbeddedServer.class, properties)) { (1)
            FruitClient fruitClient = embeddedServer.getApplicationContext().getBean(FruitClient.class);
            assertEquals(2, numberOfFruits(fruitClient));
            fruitClient.delete(apple);
            fruitClient.delete(new FruitCommand(bananaName, bananaDescription));
        }
        try (EmbeddedServer embeddedServer = ApplicationContext.run(EmbeddedServer.class, properties)) { (1)
            FruitClient fruitClient = embeddedServer.getApplicationContext().getBean(FruitClient.class);
            assertEquals(0, numberOfFruits(fruitClient));
        }
    }

    private int numberOfFruits(FruitClient fruitClient) {
        return fruitsList(fruitClient).size();
    }

    private List<Fruit> fruitsList(FruitClient fruitClient) {
        return fruitsStream(fruitClient)
                .collect(Collectors.toList());
    }

    private Stream<Fruit> fruitsStream(FruitClient fruitClient) {
        Iterable<Fruit> fruits = fruitClient.list();
        return StreamSupport.stream(fruits.spliterator(), false);
    }
}

1	Start and stop application to verify the data is persisted to disk by MicroStream and can be retrieved after application restart.

5. Testing the Application

To run the tests:

./gradlew test

Then open build/reports/tests/test/index.html in a browser to see the results.

6. Running the Application

To run the application, use the ./gradlew run command, which starts the application on port 8080.

Create a new fruit

curl -i -d '{"name":"Pear"}' \
     -H "Content-Type: application/json" \
     -X POST http://localhost:8080/fruits

Output

HTTP/1.1 201 Created
date: Thu, 12 May 2022 13:45:56 GMT
Content-Type: application/json
content-length: 16
connection: keep-alive

{"name":"Pear"}

Get a list of all fruits

curl -i localhost:8080/fruits

Output

HTTP/1.1 200 OK
date: Thu, 12 May 2022 13:46:54 GMT
Content-Type: application/json
content-length: 70
connection: keep-alive

[{"name":"Pear"}]

7. MicroStream REST and GUI

Often, during development is useful to see the data being saved by MicroStream. Micronaut MicroStream integration helps to do that.

Add the following dependency:

build.gradle

developmentOnly("io.micronaut.microstream:micronaut-microstream-rest")

The above dependency provides several JSON endpoints which expose the contents of the MicroStream storage.

7.1. MicroStream Client GUI

Download MicroStream client GUI.

Run the client and connect to the MicroStream REST API exposed by the Micronaut application:

You can visualize the data you saved via cURL.

8. Next steps

Explore more features with Micronaut Guides.

Read more about the Micronaut MicroStream integration. Read more about MicroStream for Java.

Read more about Micronaut Serialization.

9. Sponsors

MicroStream sponsored the creation of this Guide.

10. License

All guides are released with an Apache license 2.0 license for the code and a Creative Commons Attribution 4.0 license for the writing and media (images…).

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