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Developer's guide - Foundations

The Foundations section of the Temporal Developer's guide covers the minimum set of concepts and implementation details needed to build and run a Temporal ApplicationLink preview iconWhat is a Temporal Application

A Temporal Application is a set of Workflow Executions.

Learn more—that is, all the relevant steps to start a Workflow Execution that executes an Activity.

WORK IN PROGRESS

This guide is a work in progress. Some sections may be incomplete or missing for some languages. Information may change at any time.

If you can't find what you are looking for in the Developer's guide, it could be in older docs for SDKs.

In this section you can find the following:

Run a development Cluster​

The following sections list various methods of deploying your Temporal ClustersLink preview iconWhat is a Temporal Cluster?

A Temporal Cluster is the Temporal Server paired with persistence.

Learn more locally, so that you can use and interact with the Temporal ClientLink preview iconWhat is a Temporal Client

A Temporal Client, provided by a Temporal SDK, provides a set of APIs to communicate with a Temporal Cluster.

Learn more APIs and tctl commands to test and develop applications.

The following sections list methods for deploying your Temporal development Clusters.

  • Temporalite: This distribution of Temporal runs as a single process with zero runtime dependencies.
  • Docker: Using Docker Compose simplifies developing your Temporal Application.
  • Gitpod: One-click deployments are available for Go and TypeScript.

For information on deploying a production environment, see the Temporal Cloud documentation.

Temporalite​

Temporalite is a distribution of Temporal that runs as a single process with zero runtime dependencies. It supports persistence to disk and in-memory mode through SQLite.

Prerequisites

Temporalite requires Go 1.18 or later.

Build and start Temporalite

The following steps start and run a Temporal Cluster.

  1. Build from source.
    git clone https://github.com/temporalio/temporalite.git
    cd temporalite
    go build ./cmd/temporalite
  2. Start Temporalite by using the start command.
    ./temporalite start --namespace default
    Replace default with your Namespace Name.

Results: You should have Temporal Cluster running at http://127.0.0.1:7233 and the Temporal Web UI at http://127.0.0.1:8233.

Docker Compose​

Use Docker Compose and Temporal Cluster Docker images to quickly install and run a Temporal Cluster locally while developing Temporal Applications.

Prerequisites

Install Docker and Docker Compose.

Clone the repo and run Docker Compose

The following steps start and run a Temporal Cluster using the default configuration.

  1. Clone the temporalio/docker-compose repository.
    git clone https://github.com/temporalio/docker-compose.git
  2. Change to the directory for the project.
    cd docker-compose
  3. From your project directory, start your application.
    docker compose up

Results: You should have Temporal Cluster running at http://127.0.0.1:7233 and the Temporal Web UI at http://127.0.0.1:8080.

To try other configurations (different dependencies and databases), or to try a custom Docker image, follow the temporalio/docker-compose README.

Gitpod​

Run a Temporal Cluster and develop Temporal Applications in your browser using Gitpod.

One-click deployments are available for the temporalio/samples-go repo and the temporalio/samples-typescript repo.

A one-click deployment starts a Temporal Cluster using a Temporal Cluster Docker image, starts a Worker Process, and starts one of the application's sample Workflows.

A one-click deployment can take up to a full minute to get fully up and running. When it is running, you can customize the application samples.

Install a Temporal SDK​

A Temporal SDKLink preview iconWhat is a Temporal SDK?

A Temporal SDK is a language-specific library that offers APIs to construct and use a Temporal Client to communicate with a Temporal Cluster, develop Workflow Definitions, and develop Worker Programs.

Learn more provides a framework for Temporal ApplicationLink preview iconWhat is a Temporal Application

A Temporal Application is a set of Workflow Executions.

Learn more development.

An SDK provides you with the following:

Build Status Coverage Status Go reference

Add the Temporal Go SDK to your project:

go get go.temporal.io/sdk

Or clone the Go SDK repo to your preferred location:

git clone git@github.com:temporalio/sdk-go.git

API reference​

Each SDK has its own API reference. Select a programming language and follow the link to be taken to that reference page.

The Temporal Go SDK API reference is published on pkg.go.dev.

Code samples​

You can find a complete list of executable code samples in Temporal's GitHub repository.

Additionally, several of the Tutorials are backed by a fully executable template application.

Connect to a Cluster​

A Temporal ClientLink preview iconWhat is a Temporal Client

A Temporal Client, provided by a Temporal SDK, provides a set of APIs to communicate with a Temporal Cluster.

Learn more enables you to communicate with the Temporal ClusterLink preview iconWhat is a Temporal Cluster?

A Temporal Cluster is the Temporal Server paired with persistence.

Learn more. Communication with a Temporal Cluster includes, but isn't limited to, the following:

  • Starting Workflow Executions.
  • Sending Signals to Workflow Executions.
  • Sending Queries to Workflow Executions.
  • Getting the results of a Workflow Execution.
  • Providing an Activity Task Token.
caution

A Temporal Client cannot be initialized and used inside a Workflow. However, it is acceptable and common to use a Temporal Client inside an Activity to communicate with a Temporal Cluster.

When you are running a Cluster locally (such as TemporaliteLink preview iconHow to quickly install a Temporal Cluster for testing and local development

There are four ways to quickly install and run a Temporal Cluster.

Learn more), the number of connection options you must provide is minimal. Many SDKs default to the local host or IP address and port that Temporalite and Docker ComposeLink preview iconHow to quickly install a Temporal Cluster for testing and local development

There are four ways to quickly install and run a Temporal Cluster.

Learn more serve (127.0.0.1:7233).

When you are connecting to a production Cluster (such as Temporal Cloud), you will likely need to provide additional connection and client options that might include, but aren't limited to, the following:

For more information about managing and generating client certificates for Temporal Cloud, see How to manage certificates in Temporal Cloud.

For more information about configuring TLS to secure inter and intra network communication for a Temporal Cluster, see Temporal Customization Samples.

Use the Dial() API available in the go.temporal.io/sdk/client package to create a new Client.

If you don't provide HostPort, the Client defaults the address and port number to 127.0.0.1:7233.

Set a custom Namespace name in the Namespace field on an instance of the Client Options.

Use the ConnectionOptions API to connect a Client with mTLS.

import (
  // ...

  "go.temporal.io/sdk/client"
)
func main() {
    cert, err := tls.LoadX509KeyPair(clientCertPath, clientKeyPath)
    if err != nil {
        return err
    }
    client, err := client.Dial(client.Options{
        HostPort:  "your-custom-namespace.tmprl.cloud:7233",
        Namespace: "your-custom-namespace",
        ConnectionOptions: client.ConnectionOptions{
            TLS: &tls.Config{Certificates: []tls.Certificate{cert}},
        },
    }
    defer temporalClient.Close()
  // ...
}

Develop Workflows​

Workflows are the fundamental unit of a Temporal Application, and it all starts with the development of a Workflow DefinitionLink preview iconWhat is a Workflow Definition?

A Workflow Definition is the code that defines the constraints of a Workflow Execution.

Learn more.

In the Temporal Go SDK programming model, a Workflow DefinitionLink preview iconWhat is a Workflow Definition?

A Workflow Definition is the code that defines the constraints of a Workflow Execution.

Learn more is an exportable function. Below is an example of a basic Workflow Definition.

View source code
package yourapp

import (
    "time"

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

// YourSimpleWorkflowDefintiion is the most basic Workflow Defintion.
func YourSimpleWorkflowDefinition(ctx workflow.Context) error {
    // ...
    return nil
}

Workflow parameters​

Temporal Workflows may have any number of custom parameters. However, we strongly recommend that objects are used as parameters, so that the object's individual fields may be altered without breaking the signature of the Workflow. All Workflow Definition parameters must be serializable.

The first parameter of a Go-based Workflow Definition must be of the workflow.Context type. It is used by the Temporal Go SDK to pass around Workflow Execution context, and virtually all the Go SDK APIs that are callable from the Workflow require it. It is acquired from the go.temporal.io/sdk/workflow package.

The workflow.Context entity operates similarly to the standard context.Context entity provided by Go. The only difference between workflow.Context and context.Context is that the Done() function, provided by workflow.Context, returns workflow.Channel instead of the standard Go chan.

Additional parameters can be passed to the Workflow when it is invoked. A Workflow Definition may support multiple custom parameters, or none. These parameters can be regular type variables or safe pointers. However, the best practice is to pass a single parameter that is of a struct type, so there can be some backward compatibility if new parameters are added.

All Workflow Definition parameters must be serializable and can't be channels, functions, variadic, or unsafe pointers.

View source code
package yourapp

import (
    "time"

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


// YourWorkflowParam is the object passed to the Workflow.
type YourWorkflowParam struct {
    WorkflowParamX string
    WorkflowParamY int
}
// ...
// YourWorkflowDefinition is your custom Workflow Definition.
func YourWorkflowDefinition(ctx workflow.Context, param YourWorkflowParam) (*YourWorkflowResultObject, error) { 
// ...
}

Workflow return values​

Workflow return values must also be serializable. Returning results, returning errors, or throwing exceptions is fairly idiomatic in each language that is supported. However, Temporal APIs that must be used to get the result of a Workflow Execution will only ever receive one of either the result or the error.

A Go-based Workflow Definition can return either just an error or a customValue, error combination. Again, the best practice here is to use a struct type to hold all custom values. A Workflow Definition written in Go can return both a custom value and an error. However, it's not possible to receive both a custom value and an error in the calling process, as is normal in Go. The caller will receive either one or the other. Returning a non-nil error from a Workflow indicates that an error was encountered during its execution and the Workflow Execution should be terminated, and any custom return values will be ignored by the system.

View source code
package yourapp

import (
    "time"

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

// YourWorkflowResultObject is the object returned by the Workflow.
type YourWorkflowResultObject struct {
    WFResultFieldX string
    WFResultFieldY int
}
// ...
// YourWorkflowDefinition is your custom Workflow Definition.
func YourWorkflowDefinition(ctx workflow.Context, param YourWorkflowParam) (*YourWorkflowResultObject, error) { 
// ...
    if err != nil {
        return nil, err
    }
    // Make the results of the Workflow Execution available.
    workflowResult := &YourWorkflowResultObject{
        WFResultFieldX: activityResult.ResultFieldX,
        WFResultFieldY: activityResult.ResultFieldY,
    }
    return workflowResult, nil
}

Workflow Type​

Workflows have a Type that are referred to as the Workflow name.

The following examples demonstrate how to set a custom name for your Workflow Type.

In Go, by default, the Workflow Type name is the same as the function name.

To customize the Workflow Type, set the Name parameter with RegisterOptions when registering your Workflow with a WorkerLink preview iconHow to develop a Worker in Go

Develop an instance of a Worker by calling worker.New(), available via the go.temporal.io/sdk/worker package.

Learn more.

View source code
package main

import (
    "log"

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

    "documentation-samples-go/yourapp"
)
// ...
func main() {
// ...
    yourWorker := worker.New(temporalClient, "your-custom-task-queue-name", worker.Options{})
// ...
    // Use RegisterOptions to set the name of the Workflow Type for example.
    registerWFOptions := workflow.RegisterOptions{
        Name: "JustAnotherWorkflow",
    }
    yourWorker.RegisterWorkflowWithOptions(yourapp.YourSimpleWorkflowDefinition, registerWFOptions)
// ...
}

Workflow logic requirements​

Workflow logic is constrained by deterministic execution requirementsLink preview iconWhat is a Workflow Definition?

A Workflow Definition is the code that defines the constraints of a Workflow Execution.

Learn more. Therefore, each language is limited to the use of certain idiomatic techniques. However, each Temporal SDK provides a set of APIs that can be used inside your Workflow to interact with external (to the Workflow) application code.

In Go, Workflow Definition code cannot directly do the following:

  • Iterate over maps using range, because with range the order of the map's iteration is randomized. Instead you can collect the keys of the map, sort them, and then iterate over the sorted keys to access the map. This technique provides deterministic results. You can also use a Side Effect or an Activity to process the map instead.
  • Call an external API, conduct a file I/O operation, talk to another service, etc. (Use an Activity for these.)

The Temporal Go SDK has APIs to handle equivalent Go constructs:

View source code

Develop Activities​

One of the primary things that Workflows do is orchestrate the execution of Activities. An Activity is a normal function or method execution that's intended to execute a single, well-defined action (either short or long-running), such as querying a database, calling a third-party API, or transcoding a media file. An Activity can interact with world outside the Temporal Platform or use a Temporal Client to interact with a Cluster. For the Workflow to be able to execute the Activity, we must define the Activity DefinitionLink preview iconWhat is an Activity Definition?

An Activity Definition is the code that defines the constraints of an Activity Task Execution.

Learn more.

In the Temporal Go SDK programming model, an Activity Definition is an exportable function or a struct method. Below is an example of both a basic Activity Definition and of an Activity defined as a Struct method. An Activity struct can have more than one method, with each method acting as a separate Activity Type. Activities written as struct methods can use shared struct variables, such as:

  • an application level DB pool
  • client connection to another service
  • reusable utilities
  • any other expensive resources that you only want to initialize once per process

Because this is such a common need, the rest of this guide shows Activities written as struct methods.

View source code
package yourapp

import (
    "context"

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

// YourSimpleActivityDefinition is a basic Activity Definiton.
func YourSimpleActivityDefinition(ctx context.Context) error {
    return nil
}

// YourActivityObject is the struct that maintains shared state across Activities.
// If the Worker crashes this Activity object loses its state.
type YourActivityObject struct {
    Message *string
    Number *int
}

// YourActivityDefinition is your custom Activity Definition.
// An Activity Definiton is an exportable function.
func (a *YourActivityObject) YourActivityDefinition(ctx context.Context, param YourActivityParam) (*YourActivityResultObject, error) {
// ...
}

Activity parameters​

There is no explicit limit to the total number of parameters that an Activity DefinitionLink preview iconWhat is an Activity Definition?

An Activity Definition is the code that defines the constraints of an Activity Task Execution.

Learn more may support. However, there is a limit of the total size of the data ends up encoded into a gRPC message Payload.

A single argument is limited to a maximum size of 2 MB. And the total size of a gRPC message, which includes all the arguments, is limited to a maximum of 4 MB.

Also, keep in mind that all Payload data is recorded in the Workflow Execution Event HistoryLink preview iconWhat is an Event History?

An append log of Events that represents the full state a Workflow Execution.

Learn more and large Event Histories can affect Worker performance. This is because the entire Event History could be transferred to a Worker Process with a Workflow TaskLink preview iconWhat is a Workflow Task?

A Workflow Task is a Task that contains the context needed to make progress with a Workflow Execution.

Learn more.

Some SDKs require that you pass context objects, others do not. When it comes to your application data—that is, data that is serialized and encoded into a Payload—we recommend that you use a single object as an argument that wraps the application data passed to Activities. This is so that you can change what data is passed to the Activity without breaking a function or method signature.

The first parameter of an Activity Definition is context.Context. This parameter is optional for an Activity Definition, though it is recommended, especially if the Activity is expected to use other Go SDK APIs.

An Activity Definition can support as many other custom parameters as needed. However, all parameters must be serializable (parameters can’t be channels, functions, variadic, or unsafe pointers), and it is recommended to pass a single struct that can be updated later.

View source code
// YourActivityParam is the struct passed to your Activity.
// Use a struct so that your function signature remains compatible if fields change.
type YourActivityParam struct {
    ActivityParamX string
    ActivityParamY int
}
// ...
func (a *YourActivityObject) YourActivityDefinition(ctx context.Context, param YourActivityParam) (*YourActivityResultObject, error) {
// ...
}

Activity return values​

All data returned from an Activity must be serializable.

There is no explicit limit to the amount of data that can be returned by an Activity, but keep in mind that all return values are recorded in a Workflow Execution Event HistoryLink preview iconWhat is an Event History?

An append log of Events that represents the full state a Workflow Execution.

Learn more.

A Go-based Activity Definition can return either just an error or a customValue, error combination (same as a Workflow Definition). You may wish to use a struct type to hold all custom values, just keep in mind they must all be serializable.

View source code
// YourActivityResultObject is the struct returned from your Activity.
// Use a struct so that you can return multiple values of different types.
// Additionally, your function signature remains compatible if the fields change.
type YourActivityResultObject struct {
    ResultFieldX string
    ResultFieldY int
}
// ...
func (a *YourActivityObject) YourActivityDefinition(ctx context.Context, param YourActivityParam) (*YourActivityResultObject, error) {
// ...
    result := &YourActivityResultObject{
        ResultFieldX: "Success",
        ResultFieldY: 1,
    }
    // Return the results back to the Workflow Execution.
    // The results persist within the Event History of the Workflow Execution.
    return result, nil
}

Activity Type​

Activities have a Type that are referred to as the Activity name. The following examples demonstrate how to set a custom name for your Activity Type.

View source code
func main() {
// ...
    yourWorker := worker.New(temporalClient, "your-custom-task-queue-name", worker.Options{})
// ...
    // Use RegisterOptions to change the name of the Activity Type for example.
    registerAOptions := activity.RegisterOptions{
        Name: "JustAnotherActivity",
    }
    yourWorker.RegisterActivityWithOptions(yourapp.YourSimpleActivityDefinition, registerAOptions)
    // Run the Worker
    err = yourWorker.Run(worker.InterruptCh())
// ...
}

Activity Execution​

Calls to spawn Activity ExecutionsLink preview iconWhat is an Activity Execution?

An Activity Execution is the full chain of Activity Task Executions.

Learn more are written within a Workflow DefinitionLink preview iconWhat is a Workflow Definition?

A Workflow Definition is the code that defines the constraints of a Workflow Execution.

Learn more. The call to spawn an Activity Execution generates the ScheduleActivityTask Command. This results in the set of three Activity TaskLink preview iconWhat is an Activity Task?

An Activity Task contains the context needed to make an Activity Task Execution.

Learn more related Events (ActivityTaskScheduled, ActivityTaskStarted, and ActivityTask[Closed])in your Workflow Execution Event History.

A single instance of the Activities implementation is shared across multiple simultaneous Activity invocations. Therefore, the Activity implementation code must be stateless.

The values passed to Activities through invocation parameters or returned through a result value are recorded in the Execution history. The entire Execution history is transferred from the Temporal service to Workflow Workers when a Workflow state needs to recover. A large Execution history can thus adversely impact the performance of your Workflow.

Therefore, be mindful of the amount of data you transfer through Activity invocation parameters or Return Values. Otherwise, no additional limitations exist on Activity implementations.

To spawn an Activity ExecutionLink preview iconWhat is an Activity Execution?

An Activity Execution is the full chain of Activity Task Executions.

Learn more, call ExecuteActivity() inside your Workflow Definition. The API is available from the go.temporal.io/sdk/workflow package. The ExecuteActivity() API call requires an instance of workflow.Context, the Activity function name, and any variables to be passed to the Activity Execution. The Activity function name can be provided as a variable object (no quotations) or as a string. The benefit of passing the actual function object is that the framework can validate the parameters against the Activity Definition. The ExecuteActivity call returns a Future, which can be used to get the result of the Activity Execution.

View source code
func YourWorkflowDefinition(ctx workflow.Context, param YourWorkflowParam) (*YourWorkflowResultObject, error) { 
    // Set the options for the Activity Execution.
    // Either StartToClose Timeout OR ScheduleToClose is required.
    // Not specifying a Task Queue will default to the parent Workflow Task Queue.
    activityOptions := workflow.ActivityOptions{
        StartToCloseTimeout: 10 * time.Second,
    }
    ctx = workflow.WithActivityOptions(ctx, activityOptions)
    activityParam := YourActivityParam{
        ActivityParamX: param.WorkflowParamX,
        ActivityParamY: param.WorkflowParamY,
    }
    // Use a nil struct pointer to call Activities that are part of a struct.
    var a *YourActivityObject
    // Execute the Activity and wait for the result.
    var activityResult *YourActivityResultObject
    err := workflow.ExecuteActivity(ctx, a.YourActivityDefinition, activityParam).Get(ctx, &activityResult)
    if err != nil {
        return nil, err
    }
// ...
}

Required timeout​

Activity Execution semantics rely on several parameters. The only required value that needs to be set is either a Schedule-To-Close TimeoutLink preview iconWhat is a Start-To-Close Timeout?

A Start-To-Close Timeout is the maximum time allowed for a single Activity Task Execution.

Learn more or a Start-To-Close TimeoutLink preview iconWhat is a Start-To-Close Timeout?

A Start-To-Close Timeout is the maximum time allowed for a single Activity Task Execution.

Learn more. These values are set in the Activity Options.

Get Activity results​

The call to spawn an Activity ExecutionLink preview iconWhat is an Activity Execution?

An Activity Execution is the full chain of Activity Task Executions.

Learn more generates the ScheduleActivityTask Command and provides the Workflow with an Awaitable. Workflow Executions can either block progress until the result is available through the Awaitable or continue progressing, making use of the result when it becomes available.

The ExecuteActivity API call returns an instance of workflow.Future which has the following two methods:

  • Get(): Takes an instance of the workflow.Context, that was passed to the Activity Execution, and a pointer as parameters. The variable associated with the pointer is populated with the Activity Execution result. This call blocks until the results are available.
  • IsReady(): Returns true when the result of the Activity Execution is ready.

Call the Get() method on the instance of workflow.Future to get the result of the Activity Execution. The type of the result parameter must match the type of the return value declared by the Activity function.

func YourWorkflowDefinition(ctx workflow.Context, param YourWorkflowParam) (YourWorkflowResponse, error) {
 // ...
 future := workflow.ExecuteActivity(ctx, YourActivityDefinition, yourActivityParam)
 var yourActivityResult YourActivityResult
 if err := future.Get(ctx, &yourActivityResult); err != nil {
   // ...
 }
 // ...
}

Use the IsReady() method first to make sure the Get() call doesn't cause the Workflow Execution to wait on the result.

func YourWorkflowDefinition(ctx workflow.Context, param YourWorkflowParam) (YourWorkflowResponse, error) {
 // ...
 future := workflow.ExecuteActivity(ctx, YourActivityDefinition, yourActivityParam)
 // ...
 if(future.IsReady()) {
   var yourActivityResult YourActivityResult
   if err := future.Get(ctx, &yourActivityResult); err != nil {
     // ...
   }
 }
 // ...
}

It is idiomatic to invoke multiple Activity Executions from within a Workflow. Therefore, it is also idiomatic to either block on the results of the Activity Executions or continue on to execute additional logic, checking for the Activity Execution results at a later time.

Run Worker Processes​

The Worker ProcessLink preview iconWhat is a Worker Process?

A Worker Process is responsible for polling a Task Queue, dequeueing a Task, executing your code in response to a Task, and responding to the Temporal Server with the results.

Learn more is where Workflow Functions and Activity Functions are executed.

A Worker EntityLink preview iconWhat is a Worker Entity?

A Worker Entity is the individual Worker within a Worker Process that listens to a specific Task Queue.

Learn more is the component within a Worker Process that listens to a specific Task Queue.

Although multiple Worker Entities can be in a single Worker Process, a single Worker Entity Worker Process may be perfectly sufficient. For more information, see the Worker tuning guide.

A Worker Entity contains both a Workflow Worker and an Activity Worker so that it can make progress for either a Workflow Execution or an Activity Execution.

Create an instance of Worker by calling worker.New(), available through the go.temporal.io/sdk/worker package, and pass it the following parameters:

  1. An instance of the Temporal Go SDK Client.
  2. The name of the Task Queue that it will poll.
  3. An instance of worker.Options, which can be empty.

Then, register the Workflow Types and the Activity Types that the Worker will be capable of executing.

Lastly, call either the Start() or the Run() method on the instance of the Worker. Run accepts an interrupt channel as a parameter, so that the Worker can be stopped in the terminal. Otherwise, the Stop() method must be called to stop the Worker.

tip

If you have gow installed, the Worker Process automatically "reloads" when you update the Worker file:

go install github.com/mitranim/gow@latest
gow run worker/main.go # automatically reloads when file changes
View source code
package main

import (
    "log"

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

    "documentation-samples-go/yourapp"
)


func main() {
    // Create a Temporal Client
    // A Temporal Client is a heavyweight object that should be created just once per process.
    temporalClient, err := client.Dial(client.Options{})
    if err != nil {
        log.Fatalln("Unable to create client", err)
    }
    defer temporalClient.Close()
    // Create a new Worker.
    yourWorker := worker.New(temporalClient, "your-custom-task-queue-name", worker.Options{})
    // Register your Workflow Definitions with the Worker.
    // Use the ReisterWorkflow or RegisterWorkflowWithOptions method for each Workflow registration.
    yourWorker.RegisterWorkflow(yourapp.YourWorkflowDefinition)
// ...
    // Register your Activity Definitons with the Worker.
    // Use this technique for registering all Activities that are part of a struct and set the shared variable values.
    message := "This could be a connection string or endpoint details"
    number := 100
    activities := &yourapp.YourActivityObject{
        Message: &message,
        Number: &number,
    }
    // Use the RegisterActivity or RegisterActivityWithOptions method for each Activity.
    yourWorker.RegisterActivity(activities)
// ...
    // Run the Worker
    err = yourWorker.Run(worker.InterruptCh())
    if err != nil {
        log.Fatalln("Unable to start Worker", err)
    }
}
// ...

Register types​

All Workers listening to the same Task Queue name must be registered to handle the exact same Workflows Types and Activity Types.

If a Worker polls a Task for a Workflow Type or Activity Type it does not know about, it fails that Task. However, the failure of the Task does not cause the associated Workflow Execution to fail.

The RegisterWorkflow() and RegisterActivity() calls essentially create an in-memory mapping between the Workflow Types and their implementations, inside the Worker process.

Registering Activity structs

Per Activity DefinitionLink preview iconHow to develop an Activity Definition in Go

In the Temporal Go SDK programming model, an Activity Definition is an exportable function or a struct method.

Learn more best practices, you might have an Activity struct that has multiple methods and fields. When you use RegisterActivity() for an Activity struct, that Worker has access to all exported methods.

Registering multiple Types

To register multiple Activity Types and/or Workflow Types with the Worker Entity, just make multiple Activity registration calls, but make sure each Type name is unique:

w.RegisterActivity(ActivityA)
w.RegisterActivity(ActivityB)
w.RegisterActivity(ActivityC)
w.RegisterWorkflow(WorkflowA)
w.RegisterWorkflow(WorkflowB)
w.RegisterWorkflow(WorkflowC)

Start Workflow Execution​

Workflow Execution semantics rely on several parameters—that is, to start a Workflow Execution you must supply a Task Queue that will be used for the Tasks (one that a Worker is polling), the Workflow Type, language-specific contextual data, and Workflow Function parameters.

In the examples below, all Workflow Executions are started using a Temporal Client. To spawn Workflow Executions from within another Workflow Execution, use either the Child Workflow or External Workflow APIs.

See the Customize Workflow Type section to see how to customize the name of the Workflow Type.

A request to spawn a Workflow Execution causes the Temporal Cluster to create the first Event (WorkflowExecutionStarted) in the Workflow Execution Event History. The Temporal Cluster then creates the first Workflow Task, resulting in the first WorkflowTaskScheduled Event.

To spawn a Workflow Execution, use the ExecuteWorkflow() method on the Go SDK Client.

The ExecuteWorkflow() API call requires an instance of context.Context, an instance of StartWorkflowOptions, a Workflow Type name, and all variables to be passed to the Workflow Execution. The ExecuteWorkflow() call returns a Future, which can be used to get the result of the Workflow Execution.

package main

import (
  // ...

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

func main() {
  temporalClient, err := client.Dial(client.Options{})
  if err != nil {
    // ...
  }
  defer temporalClient.Close()
  // ...
  workflowOptions := client.StartWorkflowOptions{
    // ...
  }
  workflowRun, err := temporalClient.ExecuteWorkflow(context.Background(), workflowOptions, YourWorkflowDefinition, param)
  if err != nil {
    // ...
  }
  // ...
}

func YourWorkflowDefinition(ctx workflow.Context, param YourWorkflowParam) (YourWorkflowResponse, error) {
  // ...
}

If the invocation process has access to the function directly, then the Workflow Type name parameter can be passed as if the function name were a variable, without quotations.

workflowRun, err := temporalClient.ExecuteWorkflow(context.Background(), workflowOptions, YourWorkflowDefinition, param)

If the invocation process does not have direct access to the statically defined Workflow Definition, for example, if the Workflow Definition is in an un-importable package, or it is written in a completely different language, then the Workflow Type can be provided as a string.

workflowRun, err := c.ExecuteWorkflow(context.Background(), workflowOptions, "YourWorkflowDefinition", param)

Set Task Queue​

In most SDKs, the only Workflow Option that must be set is the name of the Task QueueLink preview iconWhat is a Task Queue?

A Task Queue is a first-in, first-out queue that a Worker Process polls for Tasks.

Learn more.

For any code to execute, a Worker Process must be running that contains a Worker Entity that is polling the same Task Queue name.

Create an instance of StartWorkflowOptions from the go.temporal.io/sdk/client package, set the TaskQueue field, and pass the instance to the ExecuteWorkflow call.

  • Type: string
  • Default: None, this is a required field to be set by the developer
workflowOptions := client.StartWorkflowOptions{
  // ...
  TaskQueue: "your-task-queue",
  // ...
}
workflowRun, err := c.ExecuteWorkflow(context.Background(), workflowOptions, YourWorkflowDefinition)
if err != nil {
  // ...
}

Workflow Id​

Although it is not required, we recommend providing your own Workflow IdLink preview iconWhat is a Workflow Id?

A Workflow Id is a customizable, application-level identifier for a Workflow Execution that is unique to an Open Workflow Execution within a Namespace.

Learn more that maps to a business process or business entity identifier, such as an order identifier or customer identifier.

Create an instance of StartWorkflowOptions from the go.temporal.io/sdk/client package, set the ID field, and pass the instance to the ExecuteWorkflow call.

  • Type: string
  • Default: System generated UUID
workflowOptions := client.StartWorkflowOptions{
  // ...
  ID: "Your-Custom-Workflow-Id",
  // ...
}
workflowRun, err := c.ExecuteWorkflow(context.Background(), workflowOptions, YourWorkflowDefinition)
if err != nil {
  // ...
}

Get Workflow results​

If the call to start a Workflow Execution is successful, you will gain access to the Workflow Execution's Run Id.

The Workflow Id, Run Id, and Namespace may be used to uniquely identify a Workflow Execution in the system and get its result.

It's possible to both block progress on the result (synchronous execution) or get the result at some other point in time (asynchronous execution).

In the Temporal Platform, it's also acceptable to use Queries as the preferred method for accessing the state and results of Workflow Executions.

The ExecuteWorkflow call returns an instance of WorkflowRun, which is the workflowRun variable in the following line.

 workflowRun, err := c.ExecuteWorkflow(context.Background(), workflowOptions, app.YourWorkflowDefinition, param)
 if err != nil {
   // ...
 }
 // ...
}

The instance of WorkflowRun has the following three methods:

  • GetWorkflowID(): Returns the Workflow Id of the invoked Workflow Execution.
  • GetRunID(): Always returns the Run Id of the initial Run (See Continue As New) in the series of Runs that make up the full Workflow Execution.
  • Get: Takes a pointer as a parameter and populates the associated variable with the Workflow Execution result.

To wait on the result of Workflow Execution in the same process that invoked it, call Get() on the instance of WorkflowRun that is returned by the ExecuteWorkflow() call.

 workflowRun, err := c.ExecuteWorkflow(context.Background(), workflowOptions, YourWorkflowDefinition, param)
 if err != nil {
   // ...
 }
 var result YourWorkflowResponse
 err = workflowRun.Get(context.Background(), &result)
 if err != nil {
     // ...
 }
 // ...
}

However, the result of a Workflow Execution can be obtained from a completely different process. All that is needed is the Workflow Id. (A Run Id is optional if more than one closed Workflow Execution has the same Workflow Id.) The result of the Workflow Execution is available for as long as the Workflow Execution Event History remains in the system.

Call the GetWorkflow() method on an instance of the Go SDK Client and pass it the Workflow Id used to spawn the Workflow Execution. Then call the Get() method on the instance of WorkflowRun that is returned, passing it a pointer to populate the result.

 // ...
 workflowID := "Your-Custom-Workflow-Id"
 workflowRun := c.GetWorkflow(context.Background, workflowID)

 var result YourWorkflowResponse
 err = workflowRun.Get(context.Background(), &result)
 if err != nil {
     // ...
 }
 // ...

Get last completion result

In the case of a Temporal Cron JobLink preview iconWhat is a Temporal Cron Job?

A Temporal Cron Job is the series of Workflow Executions that occur when a Cron Schedule is provided in the call to spawn a Workflow Execution.

Learn more, you might need to get the result of the previous Workflow Run and use it in the current Workflow Run.

To do this, use the HasLastCompletionResult and GetLastCompletionResult APIs, available from the go.temporal.io/sdk/workflow package, directly in your Workflow code.

type CronResult struct {
 Count int
}

func YourCronWorkflowDefinition(ctx workflow.Context) (CronResult, error) {
 count := 1

 if workflow.HasLastCompletionResult(ctx) {
   var lastResult CronResult
   if err := workflow.GetLastCompletionResult(ctx, &lastResult); err == nil {
     count = count + lastResult.Count
   }
 }

 newResult := CronResult {
   Count: count,
 }
 return newResult, nil
}

This will work even if one of the cron Workflow Runs fails. The next Workflow Run gets the result of the last successfully Completed Workflow Run.