Hello World

In this guide we’ll cover how to get a very simple Orbit application running in the form of “Hello World”. It shows using a single-module in a single-process environment, often useful for development purposes. This will demonstrate how to set up an Actor and communicate with an Orbit Server.

This tutorial assumes that you have set up a development environment as described in the Getting Started Prerequisites document and have some familiarity with Gradle based Kotlin projects. All samples are in Kotlin, the language in which Orbit is developed, but the principles work for a Java app as well.

Gradle Project

The first step is to set up a Gradle project and pull in the Orbit dependencies.

implementation("cloud.orbit:orbit-client:2.0.0-alpha.108")

Actor Interface

In Orbit all actors must have an interface, below we’ll create a very simple actor interface.

greeter.kt

package orbit.hello

import orbit.client.actor.ActorWithStringKey

interface Greeter : ActorWithStringKey {
    suspend fun sayHello(): String
}

• Actor interfaces are standard Kotlin interfaces with special constraints
• All Actor interfaces must extend an Actor type
• All interface methods must return a future in the form of a Deferred or be a suspending Kotlin method
• The return type must be serializable or Unit.

Actor Implementation

Once you have an actor interface in place, the final step to complete the actor is to create an actor implementation.

greeterImpl.kt

package orbit.hello

import orbit.client.actor.AbstractActor

class GreeterImpl : AbstractActor(), Player {
{
    override suspend fun sayHello(greeting: String): String {
    {
        println("Here: ${greeting}")
        return "You said: '${greeting}', I say: 'Hello from ${context.reference.key} at node ${context.client.nodeId?.key}!'")
    }
}

• An actor implementation is a standard Kotlin or Java class
• Extending AbstractActor grants access to the context with a reference to client and the actor’s address
• The actor must implement an actor interface
• Only one actor implementation per actor interface is permitted

Using The Actor

The final step to get a working example is for us to actually use the actor.

app.kt

package orbit.hello

import orbit.hello.actors.Actor
import orbit.hello.actors.Stage

fun main() {
    runBlocking {
        val orbitClient = OrbitClient(
            OrbitClientConfig(
                namespace = "hello",
                grpcEndpoint = "dns:///localhost:50056/"
            )
        )

        orbitClient.start().join()

        val greeter = orbit.actorFactory.createProxy<Greeter>("Tim")
        val response = greeter.hello("Welcome to Orbit")
        println(response)

        orbit.stop().join()
    }
}

• We create an orbit client instance in our namespace “hello”
• We get a reference to an actor
• The framework will handle the activation of the actor.
• You can communicate with the actor without knowing it’s status.

Running Orbit Server

Assure Docker Desktop is running and Docker Compose is installed from the Prerequisites step.

In a terminal window, run the following.

> docker run -it -p 50056:50056 orbitframework/orbit:2.0.0-alpha.108
Listening for transport dt_socket at address: 5005
[main] INFO orbit.application.impl.SettingsLoader - Searching for Orbit Settings...
[main] INFO orbit.application.impl.SettingsLoader - No settings found. Using defaults.
[main] INFO orbit.server.mesh.local.LocalMeterRegistry - Starting simple meter registry
[orbit-cpu-1] INFO orbit.server.OrbitServer - Starting Orbit server...
[orbit-cpu-1] INFO orbit.server.OrbitServer - Lease expirations: Addressable: 600s, Node: 10s
[orbit-cpu-1] INFO orbit.server.pipeline.Pipeline - Started a rail worker with 32 rails and a 10000 entry buffer.
[orbit-cpu-1] INFO orbit.server.mesh.LocalNodeInfo - Joined cluster as (NodeId(key=aFmxt6MWvWP5HihR, namespace=management))
[orbit-cpu-1] INFO orbit.server.service.GrpcEndpoint - Starting gRPC Endpoint on LocalServerInfo(port=50056, url=localhost:50056).port...
[orbit-cpu-1] INFO orbit.server.service.GrpcEndpoint - gRPC Endpoint started on LocalServerInfo(port=50056, url=localhost:50056).port.
[orbit-cpu-1] INFO orbit.server.OrbitServer - Orbit server started successfully in 338ms.

Running

You should now be able to run the project. If everything has gone well, you should see output similar to the following:

Connecting to Orbit at dns:///localhost:50056/
Here: Welcome to Orbit
You said: 'Welcome to Orbit!', I say: Hello from Tim at node aFmxt6MWvWP5HihR!

Congratulations, you have created your first Orbit application!