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Version: june-2022

Workflow Clients in TypeScript

@temporalio/client NPM API reference | GitHub

Workflow Clients are embedded in your application code and connect to Temporal Server via gRPC. They are the only way to schedule new Workflow Executions with Temporal Server.

  • Workflow Clients can run in any Node.js application, for example, in a serverless function, Express.js API route handler or CLI/script run.

  • The primary use of Workflow Clients is to start new Workflow Executions (including Cron Workflows). Given a workflowId, a Workflow Client can also get a Handle to a running Workflow Execution or retrieve/wait for its result.

  • Workflow Handles are bindings to specific Workflow Executions that expose more APIs for control.

    We strongly recommend familiarizing yourself with Workflow Handle APIs because they are the main way you will signal, query, describe, cancel, terminate, and await the result of running Workflow Executions.

  • Advanced users can also use the WorkflowService exposed by a Workflow Client to make raw gRPC calls (usually for introspection).

Workflow Clients are separate from Workers, but communicate with them through Task Queues to start Workflow Executions. For more information, see Workers and Task Queues in TypeScript and Workflows in TypeScript.

Full Example

The following code is a WorkflowClient example, from our Hello World sample:

The rest of this document explains each step in detail with practical usage tips.

Create a new Workflow Client

Create a WorkflowClient with the requisite gRPC Connection:

import {Connection, WorkflowClient} from "@temporalio/client";
const connection = await Connection.connect({
address: "temporal.prod.my.org",
}); // to configure for production
const client = new WorkflowClient({connection});

If you omit the connection and just call new WorkflowClient(), it creates a default connection that will work locally. Just remember you will need to configure your Connection and Namespace when deploying to production.

Start a Workflow Execution

When you have a Workflow Client, you can schedule the start of a Workflow with client.start, specifying workflowId, taskQueue, and args and returning a Workflow Handle (see below) immediately after the Server acknowledges receipt.

// // STEP ONE: client.start
// Option 1: Specifying args and workflowId
const handle = await client.start(example, {
workflowId: "business-meaningful-id",
taskQueue: "tutorial",
args: ["foo", "bar", "baz"], // this is typechecked against workflowFn's args
});

// Option 2: Just using string name; no need to import Workflow, but no type inference
import {WorkflowStartOptions} from "@temporalio/client";
type WFType = (key: number) => Promise<string>; // arg types intentionally wrong to prove a point
const handle = await client.start<string>("example", {
workflowId: "business-meaningful-id",
taskQueue: "tutorial",
args: [123], // typechecked, but actually wrong at runtime because wrong type signature
} as WorkflowStartOptions<WFType>);

// // STEP TWO: client.getHandle
// Continue in a different process (such as a serverless function)
const handle = client.getHandle(workflowId);
const result = await handle.result(); // wait for Workflow to complete and get result. See below for other Handle APIs

// alternative combination of STEP ONE + TWO
const result = await client.execute(example /*...*/); // start and immediately wait for Workflow to complete and get result
Note: Scheduling is not the same as Starting Workflows

Calling client.start (or client.execute) merely sends a Command to Temporal Server to schedule a new Workflow Execution on the specified Task Queue; it does not actually start until a Worker (that has a matching Workflow Type) polling that Task Queue picks it up.

You can test this by executing a Workflow Client command without a matching Worker. Temporal Server records the command in Event History but does not make progress with the Workflow Execution until a Worker starts polling with a matching Task Queue and Workflow Definition.

This queuing mechanic makes your application tolerant to outages and horizontally scalable, but can be confusing to newcomers if they expect that calling client.execute(MyWorkflow) directly executes the Workflow code on the same machine as the Client.

Workflow Options

A brief guide to the WorkflowOptions available to you:

  • workflowId, taskQueue, and args (if required) are the main ones you will regularly use
  • Optional features:
  • Advanced features you probably won't need: followRuns and workflowIdReusePolicy.
caution

Workflow-level Retries and Timeouts are not recommended.

You will see that there are workflowRunTimeout, workflowExecutionTimeout, workflowTaskTimeout, and retryPolicy options in WorkflowOptions. We discourage using them unless you know what you are doing. Do not rely on Workflows to timeout or fail - you probably want to push this logic down to an Activity instead.

Workflow Handle APIs

Workflow Handles are returned after you start a Workflow (or retrieve an existing one with client.getHandle) and are bound to a single Workflow instance. They represent already-started Workflow Executions, and let you signal, query, describe, cancel, or terminate their instance:

// Get a handle if you don't already have it
const handle = client.getHandle(workflowId);

// Handle API quick examples
await handle.cancel(); // cancel with cleanup
await handle.terminate(); // kill immediately
const WFdescription = await handle.describe(); // get Workflow Execution internal info
await handle.signal<Args>(mySignal, ...args); // see Signal docs
const queryResult = await handle.query<ReturnType, Args>(myQuery, ...args); // see Query docs
const result = await handle.result(); // block until the workflow completes and/or get return value
const result = await client.execute(example /*...*/); // Alternative API for starting and immediately waiting for Workflow completion

The Workflow Handle APIs let you externally control your Workflow:

Handle APIDescription
clientReadonly accessor to the underlying Workflow Client.
workflowIdThe workflowId of the current Workflow.
firstExecutionRunIdThe runId of the initial run of the bound Workflow (available on handles created with start).
signaledRunIdThe runId of the signalled run of the bound Workflow (available on handles created with startWithStart).
query()Call to query a Workflow after it's been started even if it has already completed. const value = await handle.query(getValue, ...args);
signal()Call to signal a running Workflow. await handle.signal(increment, ...args);
cancel()Cancels a running Workflow.
terminate()Terminates a running Workflow.
describe()Describes the current Workflow Execution.
result()Promise that resolves when Workflow Execution completes.

The following covers how to use many of these APIs, you will want to be fluent with them as they cover the basics of Workflow manipulation.

Get a Workflow's result

Workflow functions may or may not return a result when they complete.

If you started a Workflow with handle.start, you can choose to wait for the result anytime with handle.result().

const handle = client.getHandle(workflowId);
const result = await handle.result(); // block until the workflow completes, if you wish

Using a Workflow Handle isn't necessary with client.execute by definition.

  • Don't forget to handle errors here. If you call result() on a Workflow that prematurely ended for some reason, it throws a WorkflowFailedError error that reflects that reason.

    const handle = client.getHandle(workflowId);
    try {
    const result = await handle.result(); // block until the workflow completes, if you wish
    } catch (err) {
    if (err instanceof WorkflowFailedError) {
    throw new Error("Temporal workflow failed: " + workflowId, {
    cause: err,
    });
    } else {
    throw new Error("error from Temporal workflow " + workflowId, {
    cause: err,
    });
    }
    }
  • You can also specify a runId, but you will almost never need it, because most people only want the results of the latest run (a Workflow may run multiple times if failed or continued as new).

Cancel a Workflow

To cancel a Workflow Execution, call the handle.cancel() method on a Workflow Handle.

// Start the Workflow without waiting its completion
await handle.start(args);
// ... Later on, cancel the workflow
await handle.cancel();

With handle.cancel(), Timers and Child Workflows have the opportunity to execute cleanup code. If you wish to skip that, you can also handle.terminate() forcefully.

Temporal gives you fine grained control over what happens when you cancel a workflow. See our docs on Cancellation Scopes for details and examples.

Scheduling Cron Workflows

You can set each workflow to repeat on a schedule with the cronSchedule option:

const handle = await client.start(scheduledWorkflow, {
workflowId: "business-meaningful-id",
taskQueue: "tutorial",
cronSchedule: "* * * * *", // start every minute
});
Should I use Cron Workflows or Timers?

This section is specifically about Temporal Cron Jobs, which are Workflows that have the cronSchedule option set in Temporal. Because Temporal Workflows have Timers, can loop indefinitely, and can spawn Child Workflows, it is natural to ask when to use which.

Cron Workflows are rigid and come with a lot of caveats. They are a great choice if you have Workflows that need to run as rigidly as the native Linux cron utility (except distributed and fault tolerant). However, if you have any advanced needs (including needing overlaps, or canceling individual executions without affecting the overall schedule), use Timers.

You can set each Workflow to repeat on a schedule with the cronSchedule option:

const handle = await client.start(scheduledWorkflow, {
taskQueue: "test",
cronSchedule: "* * * * *", // start every minute
});

For more information, see the Typescript SDK workflowOptions source code.

Note: Child Workflows and External Workflows

You can start Child Workflows only from within another Workflow, and not from a Client.

Hence the main Child Workflows documentation is on the Workflow APIs page.

A lot of the same concepts about starting, executing, and signaling Workflow Executions apply:

// inside Workflow code
import {startChild} from "@temporalio/workflow";

export async function example(WFname: string, args: string[]): Promise<string> {
const childHandle = await startChild(WFname, {
// workflowId is optional only for child workflows
// task queue and other options inherited from parent, can override
args,
});
const result = await childHandle.result();
// // equivalent to
// const result = await executeChild(WFname, /* ... */)
return result;
}

You should use cancellationScopes if you need to cancel Child Workflows.

The same concept of "Workflow Handles" applies to retrieving handles for Child and External Workflows—as long as you have the Workflow Id:

// inside Workflow code
import {getExternalWorkflowHandle} from "@temporalio/workflow";

export async function CancelExternalWorkflow(wfId: string): void {
const extHandle = getExternalWorkflowHandle(wfId);
// ...
}

Again, see Workflows in TypeScript for full details.

Advanced: Making raw gRPC calls

Under the hood of a WorkflowClient, the Connection is actually powered by a WorkflowService driver that makes the raw gRPC calls to Temporal Server. This Service is capable of making a wider range of introspection calls.

Using gRPC calls is often the only way to access some of the more advanced queries you can make from Temporal Server. We highlight some queries of interest here:

getWorkflowExecutionHistory

Outputs something like:

{
events: [
HistoryEvent {
eventId: [Long],
eventTime: [Timestamp],
eventType: 1,
taskId: [Long],
workflowExecutionStartedEventAttributes: [WorkflowExecutionStartedEventAttributes]
},
HistoryEvent {
eventId: [Long],
eventTime: [Timestamp],
eventType: 5,
taskId: [Long],
workflowTaskScheduledEventAttributes: [WorkflowTaskScheduledEventAttributes]
},
HistoryEvent {
eventId: [Long],
eventTime: [Timestamp],
eventType: 6,
taskId: [Long],
workflowTaskStartedEventAttributes: [WorkflowTaskStartedEventAttributes]
}
]
}
listWorkflowExecutions

Outputs something like:

┌─────────┬───────────────────────────────────────────────────────────────────────────────────────────────────┬──────────────────────────────────┬─────────────────────────────────────────────────┬─────────────────────────────────────────────────┬────────┬───────────────┬─────────────────────────────────────────────────┬─────────────────────┬──────────────────────────────────────────────┬────────────┬──────────────────────┐
│ (index) │ execution │ type │ startTime │ closeTime │ status │ historyLength │ executionTime │ memo │ searchAttributes │ taskQueue │ stateTransitionCount │
├─────────┼───────────────────────────────────────────────────────────────────────────────────────────────────┼──────────────────────────────────┼─────────────────────────────────────────────────┼─────────────────────────────────────────────────┼────────┼───────────────┼─────────────────────────────────────────────────┼─────────────────────┼──────────────────────────────────────────────┼────────────┼──────────────────────┤
│ 0 │ WorkflowExecution { workflowId: 'my-business-id', runId: '2798482a-46d8-4f1e-ab87-1ba3f7ddda1c' } │ WorkflowType { name: 'example' } │ Timestamp { seconds: [Long], nanos: 125158275 } │ Timestamp { seconds: [Long], nanos: 263021256 } │ 2 │ [Long] │ Timestamp { seconds: [Long], nanos: 125158275 } │ Memo { fields: {} } │ SearchAttributes { indexedFields: [Object] } │ 'tutorial' │ [Long] │
│ 1 │ WorkflowExecution { workflowId: 'my-business-id', runId: '76f1171b-7a73-46a3-ba66-b77bab0b73f8' } │ WorkflowType { name: 'example' } │ Timestamp { seconds: [Long], nanos: 841243925 } │ Timestamp { seconds: [Long], nanos: 935283589 } │ 2 │ [Long] │ Timestamp { seconds: [Long], nanos: 841243925 } │ Memo { fields: {} } │ SearchAttributes { indexedFields: [Object] } │ 'tutorial' │ [Long] │
│ 2 │ WorkflowExecution { workflowId: 'my-business-id', runId: '6d1197b7-41b8-47be-89b4-f1ef3446de1a' } │ WorkflowType { name: 'example' } │ Timestamp { seconds: [Long], nanos: 425778697 } │ Timestamp { seconds: [Long], nanos: 523022091 } │ 2 │ [Long] │ Timestamp { seconds: [Long], nanos: 425778697 } │ Memo { fields: {} } │ SearchAttributes { indexedFields: [Object] } │ 'tutorial' │ [Long] │
└─────────┴───────────────────────────────────────────────────────────────────────────────────────────────────┴──────────────────────────────────┴─────────────────────────────────────────────────┴─────────────────────────────────────────────────┴────────┴───────────────┴─────────────────────────────────────────────────┴─────────────────────┴──────────────────────────────────────────────┴────────────┴──────────────────────┘

For the full list of gRPC calls, see the Methods section of the WorkflowService API reference.

Note that if you are trying to do a lot of list-then-filter operations (e.g. listClosedWorkflowExecutions), the Visibility APIs are a better choice for Temporal deployments with ElasticSearch enabled (this is enabled by default for all Temporal Cloud customers).