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External Storage - TypeScript SDK

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The Temporal Service enforces a 2 MB per-payload limit by default. This limit is configurable on self-hosted deployments. When your Workflows or Activities handle data larger than the limit, you can offload payloads to external storage, such as Amazon S3, and pass a small reference token through the Event History instead. This page shows you how to set up External Storage with Amazon S3 or Google Cloud Storage, and how to implement a custom storage driver.

For a conceptual overview of External Storage and its use cases, see External Storage.

Store and retrieve large payloads with Amazon S3 or Google Cloud Storage​

The TypeScript SDK includes storage drivers for Amazon S3 and Google Cloud Storage. Select your storage backend in the tabs that follow. Only the driver setup differs between the two. Everything after that is the same.

Prerequisites​

  • A bucket that you have read and write access to. Refer to lifecycle management to ensure that your payloads remain available for the entire lifetime of the Workflow. For multi-region durability, see Durable External Storage.

  • Credentials with permission to write objects on components that store payloads, and to read objects on components that retrieve them. Components that only retrieve payloads do not need write access, and the reverse is also true.

  • Install the driver, the client adapter for your cloud provider's SDK, and that SDK:

    npm install @temporalio/external-storage-s3 \
      @temporalio/external-storage-s3-aws-sdk \
      @aws-sdk/client-s3

Procedure​

  1. Create a storage client, wrap it in the matching driver client, and pass the result to the driver. Each cloud SDK picks up your standard credentials from the environment:

    The AWS SDK reads environment variables, an IAM role, or your AWS config file.

    import { S3Client } from '@aws-sdk/client-s3';
    import { S3StorageDriver } from '@temporalio/external-storage-s3';
    import { AwsSdkS3StorageDriverClient } from '@temporalio/external-storage-s3-aws-sdk';

    const s3Client = new S3Client({ region: 'us-east-2' });

    const driver = new S3StorageDriver({
      client: new AwsSdkS3StorageDriverClient(s3Client),
      bucket: 'my-temporal-payloads',
    });

    To route payloads to different buckets at runtime, pass a function as bucket instead of a string. The function receives the store context and the payload, and returns a bucket name.

  2. Build an ExternalStorage instance from the driver, set it on your Data Converter, and pass the converter to your Client and Worker. This step is the same for every driver. External Storage runs outside the Workflow sandbox, so you can pass the driver object directly rather than referencing it by path the way a custom Payload Converter requires:

    import { Client, Connection } from '@temporalio/client';
    import { ExternalStorage } from '@temporalio/common';
    import { Worker } from '@temporalio/worker';

    async function createClientAndWorker() {
      const dataConverter = {
        externalStorage: new ExternalStorage({ drivers: [driver] }),
      };

      const connection = await Connection.connect();
      const client = new Client({ connection, dataConverter });

      const worker = await Worker.create({
        workflowsPath: require.resolve('./workflows'),
        taskQueue: 'my-task-queue',
        dataConverter,
      });
    }

By default, payloads of 256 KiB or larger are offloaded to external storage. You can adjust this with the payloadSizeThreshold option, even setting it to 0 to externalize all payloads regardless of size. Refer to Configure payload size threshold for more information.

All Workflows and Activities running on the Worker use the storage driver automatically without changes to your business logic. Both drivers upload and download payloads concurrently, address objects by a SHA-256 hash of their contents so identical payloads are stored once, and verify that hash on retrieve. Each rejects any single payload larger than maxPayloadSize, which defaults to 50 MiB, and includes diagnostic metadata in error messages to help troubleshoot storage failures.

Implement a custom storage driver​

If you need a storage backend other than what the built-in drivers allow, you can implement your own storage driver. Refer to Choose a storage system for guidance on selecting a backing store and Lifecycle management for retention requirements.

A shared filesystem works for local development and for Workers that mount the same volume. For anything else, use a storage system that every Client and Worker can reach.

The following sections walk through the key parts of a custom driver.

1. Implement the StorageDriver interface​

A custom driver implements the StorageDriver interface, which has two readonly properties and two methods:

  • name is a unique string that identifies the driver instance. The SDK stores this name in the claim check reference so it can route retrieval requests to the correct driver. Changing the name after payloads have been stored breaks retrieval. For example, two S3 drivers could be named "s3-primary" and "s3-archive".
  • type is a string that identifies the driver implementation, and the Worker reports it in its heartbeat. Unlike name, type must be the same across all instances of the same driver type regardless of configuration. Two S3 drivers named "s3-primary" and "s3-archive" would both report "aws.s3driver" as their type, while the built-in GCS driver reports "gcp.gcsdriver".
  • store() receives an array of payloads and returns one StorageDriverClaim per payload. A claim wraps a set of string key-value pairs that the driver uses to locate the payload later.
  • retrieve() receives the claims that store() produced and returns the original payloads.

2. Store payloads​

In store(), serialize each Payload protobuf message to bytes and write the bytes to your storage system. The application data has already been serialized by the Payload Converter and Payload Codec before it reaches the driver. See the data conversion pipeline for more details.

Return a StorageDriverClaim for each payload with enough information to retrieve it later. The context.target provides identity information and is a discriminated union: check the kind property to distinguish "workflow" from "activity", then read namespace, id, runId, and type. Consider structuring your storage keys to include this information so that you can identify which Workflow owns each payload. Within that scope, content-addressable keys, such as a SHA-256 hash of the payload bytes, can help deduplicate identical payloads. The built-in S3 and GCS drivers use this approach.

3. Retrieve payloads​

In retrieve(), download the bytes using the claim data, then reconstruct the Payload protobuf message. The Payload Converter handles deserializing the application data after the driver returns the payload.

4. Configure the Data Converter​

Pass your driver to an ExternalStorage instance on the Data Converter, and use the same converter when creating your Client and Worker. Both sides need it: a Client without External Storage configured cannot read an offloaded result. You can also package your driver as a plugin for easier reuse across services:

export function createDataConverter(rootDir: string = STORAGE_ROOT): DataConverter {
  return {
    externalStorage: new ExternalStorage({
      drivers: [new FileSystemStorageDriver({ rootDir })],
      payloadSizeThreshold: PAYLOAD_SIZE_THRESHOLD,

      // With one driver registered, every offloaded payload goes to it. Register more
      // than one and a `driverSelector` becomes required, letting you route per
      // payload: a cheap archive tier for a known-bulky Workflow type, a driver per
      // tenant, or a per-region bucket. Returning `null` from the selector keeps that
      // payload inline, which is how you exempt specific payloads from offloading.
      //
      // driverSelector: (context, _payload) =>
      //   context.target?.type === 'processDocument' ? coldDriver : hotDriver,
    }),
  };
}

Configure payload size threshold​

You can configure the payload size threshold that triggers external storage. By default, payloads of 256 KiB or larger are offloaded to external storage. You can adjust this with the payloadSizeThreshold option, or set it to 0 to externalize all payloads regardless of size. Payloads smaller than the threshold stay inline in Event History. The size compared against the threshold is that of the serialized Payload, which includes its metadata, not just your data.

const dataConverter = {
  externalStorage: new ExternalStorage({
    drivers: [driver],
    payloadSizeThreshold: 0,
  }),
};

Use multiple storage drivers​

When you register multiple drivers, you must provide a driverSelector function that chooses which driver stores each payload. ExternalStorage throws if you register more than one driver without a selector. Any driver in the list that is not selected for storing is still available for retrieval, which is useful when migrating between storage backends. Return null from the selector to keep a specific payload inline in Event History.

Multiple drivers are useful in scenarios such as:

  • Driver migration. Your Worker needs to retrieve payloads created by clients that use a different driver than the one you prefer. Register both drivers and use the selector to always pick your preferred driver for new payloads. The old driver remains available for retrieving existing claims.
  • Multi-cloud storage. Route payloads to different storage backends based on your cloud environment. For example, use S3 for Workers running on AWS and GCS for Workers running on Google Cloud. The selector chooses the appropriate driver based on the runtime environment.

Every registered driver needs a distinct name. Because S3StorageDriver defaults its name to "aws.s3driver", registering two S3 drivers requires setting the driverName option on at least one of them.

The following example registers two drivers but always selects preferredDriver for new payloads. The legacyDriver is only registered so the Worker can retrieve payloads that were previously stored with it:

const preferredDriver = new S3StorageDriver({
  client: new AwsSdkS3StorageDriverClient(s3Client),
  bucket: 'my-bucket',
});
const legacyDriver = new LegacyStorageDriver();

const externalStorage = new ExternalStorage({
  drivers: [preferredDriver, legacyDriver],
  driverSelector: () => preferredDriver,
});

Multi-region durability with Amazon S3​

To make your S3-backed External Storage tolerant of regional failures, configure the AWS side with Cross-Region Replication (CRR) and an S3 Multi-Region Access Point (MRAP), then point the driver at the MRAP ARN instead of a bucket name. See Durable External Storage for the full pattern and trade-offs.

MRAP requests are signed with SigV4A. The AWS SDK for JavaScript does not bundle a SigV4A signer, so install one alongside your existing dependencies:

npm install @aws-sdk/signature-v4a

Import the signer once during application startup. The import registers the signer with the AWS SDK, so you do not reference it directly:

import '@aws-sdk/signature-v4a';

@aws-sdk/signature-v4-crt is an alternative implementation backed by the AWS Common Runtime. When both are installed, the AWS SDK prefers the CRT implementation.

With the signer registered, the only remaining change is the value you pass as bucket:

const driver = new S3StorageDriver({
  client: new AwsSdkS3StorageDriverClient(s3Client),
  bucket: 'arn:aws:s3::123456789012:accesspoint/mfzwi23gnjvgw.mrap',
});