Restate JVM SDK

Restate is a system for easily building resilient applications using distributed durable async/await. This repository contains the Restate SDK for writing services using JVM languages.

This SDK features:

• Implement Restate services using either:
  • Java
  • Kotlin coroutines
• Deploy Restate services as:
  • Non-blocking HTTP servers
  • On AWS Lambda

Community

• 🤗️ Join our online community for help, sharing feedback and talking to the community.
• 📖 Check out our documentation to get quickly started!
• 📣 Follow us on Twitter for staying up to date.
• 🙋 Create a GitHub issue for requesting a new feature or reporting a problem.
• 🏠 Visit our GitHub org for exploring other repositories.

Using the SDK

tl;dr Use project templates

To get started, follow the Java quickstart.

Setup a project (Java)

Scaffold a project using the build tool of your choice. For example, with Gradle (Kotlin script):

gradle init --type java-application

Add the runtime dependency sdk-api and the annotation processor dependency sdk-api-gen:

annotationProcessor("dev.restate:sdk-api-gen:1.0.0")
implementation("dev.restate:sdk-api:1.0.0")

Setup a project (Kotlin)

Scaffold a project using the build tool of your choice. For example, with Gradle (Kotlin script):

gradle init --type kotlin-application

Add the Kotlin symbol processing plugin:

plugins {
    id("com.google.devtools.ksp") version "2.0.0-1.0.21"
}

Add the runtime dependency sdk-api-kotlin and the ksp dependency sdk-api-gen:

ksp("dev.restate:sdk-api-kotlin-gen:1.0.0")
implementation("dev.restate:sdk-api-kotlin:1.0.0")

Implement your first Restate component (Java)

Implement your first virtual object in a new class, for example:

import dev.restate.sdk.ObjectContext;
import dev.restate.sdk.annotation.Handler;
import dev.restate.sdk.annotation.VirtualObject;
import dev.restate.sdk.JsonSerdes;
import dev.restate.sdk.common.StateKey;

@VirtualObject
public class Greeter {

  private static final StateKey<Long> COUNT = StateKey.of("total", JsonSerdes.LONG);

  @Handler
  public String greet(ObjectContext ctx, String name) {
    long count = ctx.get(COUNT).orElse(0L);
    ctx.set(COUNT, count + 1);

    return String.format("Hello %s for the %d time!", name, count);
  }
}

When using composite types/POJOs for input/output, Jackson Databind will be used. The Jackson dependency is not automatically included, you must add it with sdk-serde-jackson:

implementation("dev.restate:sdk-serde-jackson:1.0.0")

If you want to store types/POJOs in state, use JacksonSerdes:

private static final StateKey<Person> PERSON = StateKey.of("person", JacksonSerdes.of(Person.class));

Implement your first Restate component (Kotlin)

Implement your first virtual object in a new class, for example:

import dev.restate.sdk.annotation.Handler
import dev.restate.sdk.annotation.VirtualObject
import dev.restate.sdk.kotlin.*

@VirtualObject
class Greeter {
  companion object {
    private val COUNT = KtStateKey.json<Long>("total")
  }

  @Handler
  suspend fun greet(context: ObjectContext, name: String): String {
    val count = context.get(COUNT) ?: 0L
    context.set(COUNT, count + 1)
    return "Hello $name for the $count time!"
  }
}

When using composite data types for input/output, kotlinx.serialization will be used.

Deploy the service (HTTP Server)

To deploy the Restate service as HTTP server, add sdk-http-vertx to the dependencies. For example, in Gradle:

implementation("dev.restate:sdk-http-vertx:1.0.0")

To deploy the service, add the following code to the main. For example in Java:

public static void main(String[] args) {
  RestateHttpEndpointBuilder.builder()
        .bind(new Greeter())
        .buildAndListen();
}

In Kotlin:

fun main() {
  RestateHttpEndpointBuilder.builder()
          .bind(Greeter())
          .buildAndListen()
}

Execute the project. For example, using Gradle:

gradle run

Deploy the service (AWS Lambda)

To deploy the Restate service as Lambda, add sdk-lambda to the dependencies. For example, in Gradle:

implementation("dev.restate:sdk-lambda:1.0.0")

Configure the build tool to generate Fat-JARs, which are required by AWS Lambda to correctly load the JAR. For example, using Gradle:

plugins {
  // ...
  // The shadow plugin generates a shadow JAR ready for AWS Lambda
  id("com.github.johnrengelman.shadow").version("7.1.2")
  // ...
}

Now create the Lambda handler invoking the service. For example, in Java:

public class MyLambdaHandler extends BaseRestateLambdaHandler {
  @Override
  public void register(RestateLambdaEndpointBuilder builder) {
    builder.bind(new Greeter());
  }
}

In Kotlin:

class MyLambdaHandler : BaseRestateLambdaHandler {
  override fun register(builder: RestateLambdaEndpointBuilder) {
    builder.bind(Greeter())
  }
}

Now build the Fat-JAR. For example, using Gradle:

gradle shadowJar

You can now upload the generated Jar in AWS Lambda, and configure MyLambdaHandler as the Lambda class in the AWS UI.

Additional setup

Logging

The SDK uses log4j2 as logging facade. To enable logging, add the log4j2 implementation to the dependencies:

implementation("org.apache.logging.log4j:log4j-core:2.23.0")

And configure the logging adding the file resources/log4j2.properties:

# Set to debug or trace if log4j initialization is failing
status = warn

# Console appender configuration
appender.console.type = Console
appender.console.name = consoleLogger
appender.console.layout.type = PatternLayout
appender.console.layout.pattern = %d{yyyy-MM-dd HH:mm:ss} %-5p %notEmpty{[%X{restateInvocationTarget}]}%notEmpty{[%X{restateInvocationId}]} %c - %m%n

# Filter out logging during replay
appender.console.filter.replay.type = ContextMapFilter
appender.console.filter.replay.onMatch = DENY
appender.console.filter.replay.onMismatch = NEUTRAL
appender.console.filter.replay.0.type = KeyValuePair
appender.console.filter.replay.0.key = restateInvocationStatus
appender.console.filter.replay.0.value = REPLAYING

# Restate logs to debug level
logger.app.name = dev.restate
logger.app.level = info
logger.app.additivity = false
logger.app.appenderRef.console.ref = consoleLogger

# Root logger
rootLogger.level = info
rootLogger.appenderRef.stdout.ref = consoleLogger

The SDK injects the following additional metadata to the logging context that can be used for filtering as well:

• restateInvocationTarget: invocation target, e.g. counter.Counter/Add.
• restateInvocationId: Invocation identifier, to be used in Restate observability tools. See https://docs.restate.dev/operate/invocation#invocation-identifier.
• restateInvocationStatus: Invocation status, can be WAITING_START, REPLAYING, PROCESSING, CLOSED.

When assembling fat-jars, make sure to enable merging META-INF/services files. For more info, see apache/logging-log4j2#2099.

Tracing with OpenTelemetry

The SDK can generate additional tracing information on top of what Restate already publishes. See https://docs.restate.dev/operate/monitoring/tracing to configure Restate tracing.

You can the additional SDK tracing information by configuring the OpenTelemetry in the RestateHttpEndpointBuilder/LambdaRestateServer.

For example, to set up tracing using environment variables, add the following modules to your dependencies:

implementation("io.opentelemetry:opentelemetry-sdk-extension-autoconfigure:1.38.0")
implementation("io.opentelemetry:opentelemetry-exporter-otlp:1.38.0")

And then configure it in the Restate builder:

.withOpenTelemetry(AutoConfiguredOpenTelemetrySdk.initialize().getOpenTelemetrySdk())

By exporting the following environment variables the OpenTelemetry SDK will be automatically configured to push traces:

export OTEL_SERVICE_NAME=my-service
export OTEL_TRACES_SAMPLER=always_on
export OTEL_EXPORTER_OTLP_TRACES_ENDPOINT=http://localhost:14250

Please refer to the Opentelemetry manual instrumentation documentation and the autoconfigure documentation for more info.

Versions

This library follows Semantic Versioning.

The compatibility with Restate is described in the following table:

Restate Server\sdk-java	1.0	1.1
1.0	✅	✅
1.1	✅	✅

Contributing

We’re excited if you join the Restate community and start contributing! Whether it is feature requests, bug reports, ideas & feedback or PRs, we appreciate any and all contributions. We know that your time is precious and, therefore, deeply value any effort to contribute!

Building the SDK locally

Prerequisites:

• JDK >= 11
• Docker or Podman

To build the SDK:

./gradlew build

To run the tests:

./gradlew check

To publish local snapshots of the project:

./gradlew -DskipSigning publishToMavenLocal

To update the service-protocol git subtree:

git subtree pull --prefix sdk-core/src/main/service-protocol/ git@github.com:restatedev/service-protocol.git main --squash