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Go client - Getting started guide

In this tutorial, you will learn how to use the Go client in a Go application to interact with Camunda Cloud.

You can find the complete source code on GitHub.

Prerequisites​

Set up a project​

First, we need a new Go project. Create a new project using your IDE, or create new Go module with:

mkdir -p $GOPATH/src/github.com/zb-user/zb-example
cd $GOPATH/src/github.com/zb-user/zb-example
go mod init

To use the Zeebe Go client library, add the following dependency to your go.mod:

module github.com/zb-user/zb-example

go 1.13

require github.com/zeebe-io/zeebe/clients/go v0.26.0

Set the connection settings and client credentials as environment variables:

export ZEEBE_ADDRESS='[Zeebe API]'
export ZEEBE_CLIENT_ID='[Client ID]'
export ZEEBE_CLIENT_SECRET='[Client Secret]'
export ZEEBE_AUTHORIZATION_SERVER_URL='[OAuth API]'

Hint: When you create client credentials in Camunda Cloud you have the option to download a file with the lines above filled out for you.

Create a main.go file inside the module and add the following lines to bootstrap the Zeebe client:

package main

import (
    "context"
    "fmt"
    "github.com/zeebe-io/zeebe/clients/go/pkg/zbc"
    "github.com/zeebe-io/zeebe/clients/go/pkg/pb"
    "os"
)

func main() {
    client, err := zbc.NewClient(&zbc.ClientConfig{
        GatewayAddress: os.Getenv("ZEEBE_ADDRESS"),
    })

    if err != nil {
        panic(err)
    }

    ctx := context.Background()
    topology, err := client.NewTopologyCommand().Send(ctx)
    if err != nil {
        panic(err)
    }

    for _, broker := range topology.Brokers {
        fmt.Println("Broker", broker.Host, ":", broker.Port)
        for _, partition := range broker.Partitions {
            fmt.Println("  Partition", partition.PartitionId, ":", roleToString(partition.Role))
        }
    }
}

func roleToString(role pb.Partition_PartitionBrokerRole) string {
    switch role {
    case pb.Partition_LEADER:
        return "Leader"
    case pb.Partition_FOLLOWER:
        return "Follower"
    default:
        return "Unknown"
    }
}

Run the program.

go run main.go

You should see similar output:

Broker 0.0.0.0 : 26501
  Partition 1 : Leader

Model a workflow​

Now, we need a simple workflow we can deploy. Later, we will extend the workflow with more functionality.

Open the modeler of your choice and create a new BPMN diagram.

Add a start event named Order Placed and an end event named Order Delivered to the diagram and connect the events.

model-workflow-step-1

Set the id (the BPMN process id), and mark the diagram as executable.

Save the diagram as src/main/resources/order-process.bpmn under the project's folder.

Deploy a workflow​

Next, we want to deploy the modeled workflow to the broker.

The broker stores the workflow under its BPMN process id and assigns a version.

    // After the client is created
    ctx := context.Background()
    response, err := client.NewDeployWorkflowCommand().AddResourceFile("order-process.bpmn").Send(ctx)
    if err != nil {
        panic(err)
    }
    fmt.Println(response.String())

Run the program and verify that the workflow is deployed successfully. You should see similar the output:

key:2251799813686743 workflows:<bpmnProcessId:"order-process" version:3 workflowKey:2251799813686742 resourceName:"order-process.bpmn" >

Create a workflow instance​

We are ready to create a first instance of the deployed workflow.

A workflow instance is created of a specific version of the workflow, which can be set on creation.

    // After the workflow is deployed.
    variables := make(map[string]interface{})
    variables["orderId"] = "31243"

    request, err := client.NewCreateInstanceCommand().BPMNProcessId("order-process").LatestVersion().VariablesFromMap(variables)
    if err != nil {
        panic(err)
    }

    ctx := context.Background()

    msg, err := request.Send(ctx)
    if err != nil {
        panic(err)
    }

    fmt.Println(msg.String())

Run the program and verify that the workflow instance is created. You should see the output:

workflowKey:2251799813686742 bpmnProcessId:"order-process" version:3 workflowInstanceKey:2251799813686744

You did it!

See the workflow in action​

You want to see how the workflow instance is executed?

  1. Go to the cluster in Camunda Cloud and select it
  2. Click on the link to Operate
  3. Select the workflow order process

As you can see, a workflow instance has been started and finished.

Work on a task​

Now we want to do some work within our workflow.

First, add a few service tasks to the BPMN diagram and set the required attributes. Then extend your main.go file and activate a job which are created when the workflow instance reaches a service task.

Open the BPMN diagram in the modeler. Insert three service tasks between the start and the end event.

  • Name the first task Collect Money.
  • Name the second task Fetch Items.
  • Name the third task Ship Parcel.

model-workflow-step-2

You need to set the type of each task, which identifies the nature of the work to be performed.

  • Set the type of the first task to payment-service.
  • Set the type of the second task to fetcher-service.
  • Set the type of the third task to shipping-service.

The consolidated example looks as follows:

package main

import (
    "context"
    "fmt"
    "github.com/zeebe-io/zeebe/clients/go/pkg/entities"
    "github.com/zeebe-io/zeebe/clients/go/pkg/worker"
    "github.com/zeebe-io/zeebe/clients/go/pkg/zbc"
    "log"
    "os"
)

const ZeebeAddr = "0.0.0.0:26500"

var readyClose = make(chan struct{})

func main() {
    gatewayAddr := os.Getenv("ZEEBE_ADDRESS")
    plainText:= false

    if (gatewayAddr == "") {
        gatewayAddr = ZeebeAddr
        plainText = true
    }

    zbClient, err := zbc.NewClient(&zbc.ClientConfig{
        GatewayAddress:         gatewayAddr,
        UsePlaintextConnection: plainText,
    })

    if err != nil {
        panic(err)
    }

    // deploy workflow
    ctx := context.Background()
    response, err := zbClient.NewDeployWorkflowCommand().AddResourceFile("order-process-4.bpmn").Send(ctx)
    if err != nil {
        panic(err)
    }

    fmt.Println(response.String())

    // create a new workflow instance
    variables := make(map[string]interface{})
    variables["orderId"] = "31243"

    request, err := zbClient.NewCreateInstanceCommand().BPMNProcessId("order-process-4").LatestVersion().VariablesFromMap(variables)
    if err != nil {
        panic(err)
    }

    result, err := request.Send(ctx)
    if err != nil {
        panic(err)
    }

    fmt.Println(result.String())

    jobWorker := zbClient.NewJobWorker().JobType("payment-service").Handler(handleJob).Open()

    <-readyClose
    jobWorker.Close()
    jobWorker.AwaitClose()
}

func handleJob(client worker.JobClient, job entities.Job) {
    jobKey := job.GetKey()

    headers, err := job.GetCustomHeadersAsMap()
    if err != nil {
        // failed to handle job as we require the custom job headers
        failJob(client, job)
        return
    }

    variables, err := job.GetVariablesAsMap()
    if err != nil {
        // failed to handle job as we require the variables
        failJob(client, job)
        return
    }

    variables["totalPrice"] = 46.50
    request, err := client.NewCompleteJobCommand().JobKey(jobKey).VariablesFromMap(variables)
    if err != nil {
        // failed to set the updated variables
        failJob(client, job)
        return
    }

    log.Println("Complete job", jobKey, "of type", job.Type)
    log.Println("Processing order:", variables["orderId"])
    log.Println("Collect money using payment method:", headers["method"])

    ctx := context.Background()
    _, err = request.Send(ctx)
    if err != nil {
        panic(err)
    }

    log.Println("Successfully completed job")
    close(readyClose)
}

func failJob(client worker.JobClient, job entities.Job) {
    log.Println("Failed to complete job", job.GetKey())

    ctx := context.Background()
    _, err := client.NewFailJobCommand().JobKey(job.GetKey()).Retries(job.Retries - 1).Send(ctx)
    if err != nil {
        panic(err)
    }
}

In this example we open a job worker for jobs of type payment-service. The job worker will repeatedly poll for new jobs of the type payment-service and activate them subsequently. Each activated job will then be passed to the job handler which implements the business logic of the job worker. The handler will then complete the job with its result or fail the job if it encounters a problem while processing the job.

When you have a look at the Zeebe Monitor, then you can see that the workflow instance moved from the first service task to the next one:

When you run the above example you should see similar output:

key:2251799813686751 workflows:<bpmnProcessId:"order-process" version:4 workflowKey:2251799813686750 resourceName:"order-process.bpmn" >
workflowKey:2251799813686750 bpmnProcessId:"order-process" version:4 workflowInstanceKey:22517998136
86752
2019/06/06 20:59:50 Complete job 2251799813686760 of type payment-service
2019/06/06 20:59:50 Processing order: 31243
2019/06/06 20:59:50 Collect money using payment method: VISA

What's next?​

Yay! You finished this tutorial and learned the basic usage of the Go client.

Next steps: