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Build a Temporal "Hello World!" app from scratch in Go

Tutorial information
  • Level: ⭐ Temporal beginner
  • Time: ⏱️ ~20 minutes
  • Goals: 🙌
    • Set up, build, and test a Temporal application project from scratch using the Go SDK.
    • Become more familiar with core concepts and the application structure.

Introduction

In this tutorial you will build your first Temporal from scratch using the Go SDK

The app will consist of four pieces:

  1. An Activity: An Activity is just a function that contains your business logic. Ours will simply format some text and return it.
  2. A Workflow: Workflows are functions that organize Activity method calls. Our Workflow will orchestrate the call of a single Activity function.
  3. A Worker: Workers host the Activity and Workflow code and execute the code piece by piece.
  4. An initiator: To start a Workflow, we must send a signal to the Temporal server to tell it to track the state of the Workflow. We'll write a separate function to do this.

All of the code in this tutorial is available in the hello-world Go template repository repository.

Prerequisites

Before starting this tutorial:

This tutorial focuses on the practicalities of building an application from scratch. To better understand why you should use Temporal, we recommend that you follow the tutorial where you run a Temporal money transfer application to get a taste of its value propositions.

Scaffold Go project

In a terminal, create a new project directory named hello-world-project-template-go, or something similar and cd into it.

From the root of your new project directory, initialize a new Go module. Make sure the module path (for example, hello-world-project-template-go) matches that of the directory in which you are creating the module. Then, add the Temporal Go SDK as a project dependency:

go mod init hello-world-project-template-go/app
go get go.temporal.io/sdk@latest

Create an Activity

First, let's define our Activity. Activities are meant to handle non-deterministic code that could result in unexpected results or errors. But for this tutorial all we are doing is taking a string, appending it to "Hello", and returning it back to the Workflow.

In the Go SDK, an Activity function is just like any other exported Go function.

Create activity.go in the project root and add the following code:

activity.go

package app

import (
"fmt"
)

func ComposeGreeting(name string) (string, error) {
greeting := fmt.Sprintf("Hello %s!", name)
return greeting, nil
}

Create a Workflow

Next is our Workflow. Workflow functions are where you configure and organize the execution of Activity functions. Again, the Workflow function is defined like any other Go function. Our Workflow just calls ComposeGreeting() and returns the result.

Create workflow.go and add the following code:

workflow.go

package app

import (
"time"

"go.temporal.io/sdk/workflow"
)

func GreetingWorkflow(ctx workflow.Context, name string) (string, error) {
options := workflow.ActivityOptions{
StartToCloseTimeout: time.Second * 5,
}
ctx = workflow.WithActivityOptions(ctx, options)
var result string
err := workflow.ExecuteActivity(ctx, ComposeGreeting, name).Get(ctx, &result)
return result, err
}

Task Queues are how the Temporal server supplies information to Workers. When you start a Workflow, you tell the server which Task Queue the Workflow and/or Activities use as an information queue. We will configure our Worker to listen to the same Task Queue that our Workflow and Activities use. Since the Task Queue name is used by multiple things, let's create shared.go and define our Task Queue name there:

shared.go

package app

const GreetingTaskQueue = "GREETING_TASK_QUEUE"

Define the Worker

Our Worker hosts Workflow and Activity functions and executes them one at a time. The Worker is instructed to execute a specific function via information it pulls from the Task Queue. After it runs the code, it communicates the results back to the server.

Create worker/main.go and add the following code:

worker/main.go

package main

import (
"log"

"go.temporal.io/sdk/client"
"go.temporal.io/sdk/worker"

"hello-world-project-template-go/app"
)

func main() {
// Create the client object just once per process
c, err := client.NewClient(client.Options{})
if err != nil {
log.Fatalln("unable to create Temporal client", err)
}
defer c.Close()
// This worker hosts both Workflow and Activity functions
w := worker.New(c, app.GreetingTaskQueue, worker.Options{})
w.RegisterWorkflow(app.GreetingWorkflow)
w.RegisterActivity(app.ComposeGreeting)
// Start listening to the Task Queue
err = w.Run(worker.InterruptCh())
if err != nil {
log.Fatalln("unable to start Worker", err)
}
}

Create a Workflow starter

There are two ways to start a Workflow, via the Temporal CLI or Temporal SDK. In this tutorial we use the SDK to start the Workflow which is how most Workflows are started in live environments. Additionally, the call to the Temporal server can be made synchronously or asynchronously. Here we do it synchronously, so you will see the caller wait for the result of the Workflow.

Create start/main.go and add the following code:

start/main.go

package main

import (
"context"
"fmt"
"log"

"go.temporal.io/sdk/client"

"hello-world-project-template-go/app"
)

func main() {
// Create the client object just once per process
c, err := client.NewClient(client.Options{})
if err != nil {
log.Fatalln("unable to create Temporal client", err)
}
defer c.Close()
options := client.StartWorkflowOptions{
ID: "greeting-workflow",
TaskQueue: app.GreetingTaskQueue,
}
name := "World"
we, err := c.ExecuteWorkflow(context.Background(), options, app.GreetingWorkflow, name)
if err != nil {
log.Fatalln("unable to complete Workflow", err)
}
var greeting string
err = we.Get(context.Background(), &greeting)
if err != nil {
log.Fatalln("unable to get Workflow result", err)
}
printResults(greeting, we.GetID(), we.GetRunID())
}

func printResults(greeting string, workflowID, runID string) {
fmt.Printf("\nWorkflowID: %s RunID: %s\n", workflowID, runID)
fmt.Printf("\n%s\n\n", greeting)
}

Test the app

Let's add a simple unit test to our application to make sure things are working as expected. Create workflow_test.go and add the following code:

workflow_test.go

package app

import (
"testing"

"github.com/stretchr/testify/mock"
"github.com/stretchr/testify/require"
"go.temporal.io/sdk/testsuite"
)

func Test_Workflow(t *testing.T) {
testSuite := &testsuite.WorkflowTestSuite{}
env := testSuite.NewTestWorkflowEnvironment()
// Mock activity implementation
env.OnActivity(ComposeGreeting, mock.Anything).Return("Hello World!", nil)
env.ExecuteWorkflow(GreetingWorkflow, "World")
require.True(t, env.IsWorkflowCompleted())
require.NoError(t, env.GetWorkflowError())
var greeting string
require.NoError(t, env.GetWorkflowResult(&greeting))
require.Equal(t, "Hello World!", greeting)
}

Add the required testify packages to your go.mod file by running the following:

go get github.com/stretchr/testify/mock
go get github.com/stretchr/testify/require
go mod tidy

Run this command from the project root to execute the unit tests:

go test

Run the app

To run the app we need to start the Workflow and the Worker. You can start them in any order, but run each command from a separate terminal window.

To start the Worker run this command from the project root:

go run worker/main.go

To start the Workflow run this command from the project root:

go run start/main.go
Celebratory confetti

You have successfully built a Temporal application from scratch.

Conclusion

You now know how to build a Temporal Workflow application using the Go SDK.

Review

Answer the following questions to see if you remember some of the more important concepts from this tutorial:

What are the minimum four pieces of a Temporal Workflow application?

  1. An Activity function.
  2. A Workflow function.
  3. A Worker to host the Activity and Workflow code.
  4. A frontend to start the Workflow.

How does the Temporal server get information to the Worker?

It adds the information to a Task Queue.

True or false, Temporal Activity and Workflow functions are just normal Go functions?

True