> ## Documentation Index
> Fetch the complete documentation index at: https://trigger-v3-fix-additional-files.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Tasks

> Tasks are individual building blocks of a Run.

A [Task](/documentation/concepts/tasks) is a cached unit of work in a Job Run that are logged to the Trigger.dev UI.

<Warning>
  Any interaction with an external service (database or API) should be wrapped in a Task. Failing to
  do so could result in repeated work when runs are resumed.
</Warning>

## Why do you need tasks?

Tasks are a key building block of how Trigger.dev works, and failing to use them will result in unpredictable results. Tasks allow bits of work inside a Job Run to be cached and the results of those tasks to be reused.

This is **very important** because for a Job Run to be resumable (e.g. after a serverless function timeout, or because of a call to `io.wait()`), we need to call the `Job.run` function multiple times. If we didn't cache the results of Tasks, then we would be repeating work on each run.

```ts
client.defineJob({
  id: "new-user",
  name: "Run when a new user signs up",
  version: "1.0.0",
  trigger: eventTrigger({
    name: "new.user",
    schema: z.object({
      userId: z.string(),
    }),
  }),
  integrations: {
    resend,
  },
  run: async (payload, io, ctx) => {
    // This code will run twice. Once when the run first starts, and once after the wait
    const user = await prisma.user.findUniqueOrThrow({
      where: { id: payload.userId },
      select: { email: true, name: true },
    });

    // This code will run once, because the resend integration creates a task with the "welcome-email" cacheKey
    await io.resend.sendEmail("welcome-email", {
      to: user.email,
      from: "jane@acme.inc",
      subject: "Welcome!",
      html: welcomeEmail(user.name),
    });

    // This code will run once, because io.wait creates a task with the "wait" cacheKey
    await io.wait("wait", 60 * 60 * 3); // wait for 3 hours

    // This code will run once, because we're manually creating a task with the "my-task" cacheKey
    const response = await io.runTask(
      "my-task",
      async () => {
        return await longRunningCode(payload.userId);
      },
      { name: "My Task" }
    );

    return response;
  },
});
```

As well as powering the resumable nature of Trigger.dev, Tasks also provide:

* **Retryable** – If a Task fails, it can be retried. You can configure how (or if) a Task is retried. Full details in the [io.runTask() SDK reference](/sdk/io/runtask).
* **Logging** – Tasks are logged, so you can see what happened in a Run. Find out more about [viewing runs](/documentation/guides/viewing-runs).

## Task Cache Keys

The first param of all Tasks is a `cacheKey`. This is a unique identifier for the Task inside that Run. It is used for storing the cached result of a task. It is also used to identify the Task in the [Viewing Runs Dashboard](/documentation/guides/viewing-runs).

<Warning>It's important that cacheKey's are unique inside an individual Job Run.</Warning>

## Creating Tasks

There are **3** ways of using tasks in your code:

* Using the [io.runTask()](/sdk/io/runtask) function
* Using one of our [Integration packages](/documentation/concepts/integrations) and calling the `io.integration.runTask()` wrapper
* Using one of our [Integration packages](/documentation/concepts/integrations) and calling a task wrapper function, such as [io.slack.postMessage()](/integrations/apis/slack)

### Using `io.runTask()`

The `io.runTask()` function allows you to run a Task manually. It takes a `cacheKey` and a function to run. The function will only be run if the Task is not already cached.

```ts
const response = await io.runTask("my-task", async (task) => {
  return await longRunningCode(payload.userId);
});
```

The callback function is passed a `task` object, which can be useful for providing an idempotency key to an external service. For example, Stripe:

<Info>
  Our [Stripe Integration](integrations/apis/stripe) handles this for you automatically, this is
  just for documentation purposes
</Info>

```ts
const stripe = new Stripe(process.env.STRIPE_SECRET_KEY, {
  apiVersion: "2020-08-27",
});

await io.runTask("create-customer", async (task) => {
  await stripe.customers.create(
    {
      email: "eric@trigger.dev",
    },
    {
      idempotencyKey: task.idempotencyKey,
    }
  );
});
```

`runTask` also takes an optional 3rd argument, which allows you to customize how the Task is displayed and run. For example, you can supply a name and some properties to be displayed in the Viewing Runs Dashboard:

```ts
const response = await io.runTask(
  "my-task",
  async (task) => {
    return await longRunningCode(payload.userId);
  },
  {
    name: "My Task",
    properties: [
      {
        label: "User ID",
        value: payload.userId,
      },
    ],
    icon: "user",
  }
);
```

See the [io.runTask() SDK reference](/sdk/io/runtask) for more information.

### Using `io.integration.runTask()`

All of our [Integration packages](/documentation/concepts/integrations) expose a `runTask()` function. The main differences between this and `io.runTask()` are:

* Adds an additional callback parameter which provides the underlying authenticated integration client
* Automatically sets the `icon` property on the Task.
* Configures sensible defaults for retries and error handling.

An example here demonstrates using the GitHub integration's `runTask` function to create a project card when a new user signs up:

```ts
import { Github } from "@trigger.dev/github";

const github = new Github({
  id: "github",
});

client.defineJob({
  id: "create-project-card",
  name: "Create Project Card",
  version: "1.0.0",
  trigger: eventTrigger({
    name: "new.user",
  }),
  integrations: {
    github,
  },
  run: async (payload, io, ctx) => {
    await io.github.runTask(
      "create-card",
      async (client, task) => {
        // client is an authenticated GitHub client (https://github.com/octokit/octokit.js)
        return client.rest.projects.createCard({
          column_id: process.env.GITHUB_PROJECT_COLUMN_ID,
          note: `New User ${payload.user.name} signed up!`,
        });
      },
      { name: "Create card" }
    );
  },
});
```

### Using an Integration Task Wrapper Function

Our [Integration packages](/documentation/concepts/integrations) also expose a number of task wrapper functions. These are functions that wrap a common task for that integration. For example, the [Slack integration](/integrations/apis/slack) exposes a `postMessage()` function:

```ts
import { Slack } from "@trigger.dev/slack";

const slack = new Slack({
  id: "slack",
});

client.defineJob({
  id: "send-welcome-message",
  name: "Send welcome message",
  version: "1.0.0",
  trigger: eventTrigger({
    name: "new.user",
  }),
  integrations: {
    slack,
  },
  run: async (payload, io, ctx) => {
    await io.slack.postMessage("send-message", {
      channel: process.env.SLACK_CHANNEL_ID,
      text: `New user ${payload.user.name} signed up!`,
    });
  },
});
```

All task wrapper functions take a `cacheKey` as the first argument, because they are Tasks under the hood. Think of them as a convenience wrapper around `io.runTask()`.

We strive to document all of the task wrapper functions in our [Integration packages](/documentation/concepts/integrations). For example, checkout our [GitHub integration task](/integrations/apis/github-tasks) docs.

## Subtasks

You can break up a task into multiple subtasks. This is useful for breaking up a long-running task into smaller chunks, while consolidating the logging into a single task in the dashboard with children.

<Info>We currently support nesting up to 5 levels</Info>

```ts
const response = await io.runTask("parent-task", async (task) => {
  await io.runTask("child-1", async () => {
    // do something
  });

  await io.runTask("child-2", async () => {
    // do something
  });
});
```

Task cacheKey's are automatically scoped to the parent task. So for example, you can reuse a cacheKey inside a parent task and it will not conflict with another top-level task.

```ts
const response = await io.runTask("parent-task", async (task) => {
  await io.runTask("child-1", async () => {
    // do something
  });

  await io.runTask("child-2", async () => {
    // do something
  });
});

// This will not conflict with the child-1 task above
const response = await io.runTask("child-1", async (task) => {
  // do something
});
```

### Extracting Common Tasks

Subtasks allow you to DRY up any repeating task code into a single function. For example, if you have a common task that sends a welcome email, you can extract that into a function:

```ts
const sendWelcomeEmail = async (cacheKey: string, io: IO, resend: Resend, userId: string) => {
  return await io.runTask(cacheKey, async () => {
    const user = await io.runTask("fetch-user", async () => {
      return prisma.user.findUniqueOrThrow({
        where: { id: userId },
        select: { email: true, name: true },
      });
    });

    await io.resend.sendEmail("📧", {
      to: user.email,
      from: "eric@trigger.dev",
      subject: "Welcome!",
      html: welcomeEmail(user.name),
    });
  });
};

client.defineJob({
  id: "new-user",
  name: "Run when a new user signs up",
  version: "1.0.0",
  trigger: eventTrigger({
    name: "new.user",
    schema: z.object({
      userId: z.string(),
    }),
  }),
  integrations: {
    resend,
  },
  run: async (payload, io, ctx) => {
    await sendWelcomeEmail("🫡", io, io.resend, payload.userId);
  },
});
```

<Note>
  Always make sure you are allow passing a unique cacheKey to the `runTask` function, so the tasks
  inside the function are not accidentally reused.
</Note>

## Limitations

A single task has an upper-bound on it's execution duration, which must be less than the serverless function execution timeout of your deployed platform. For more information see our [Limits docs](/documentation/concepts/limits#maximum-task-duration)

## References

<CardGroup cols={2}>
  <Card title="Resumability" icon="clock" href="/documentation/concepts/resumability">
    Runs can be very long-running. Learn how we handle this.
  </Card>

  <Card title="Integrations" icon="grid-2" href="/documentation/concepts/integrations">
    Integrations utilize Tasks.
  </Card>

  <Card title="`io` SDK Reference" icon="wrench" href="/sdk/io">
    The `io` object allows you to easily run a Task yourself.
  </Card>

  <Card title="Viewing Runs Dashboard" icon="globe" href="/documentation/guides/viewing-runs">
    View all Runs for a Job, all the way down to individual Tasks.
  </Card>
</CardGroup>