[Yandex Cloud documentation](../../../index.md) > [Yandex API Gateway](../../index.md) > [Step-by-step guides](../index.md) > Creating a trigger > Creating a trigger for Data Streams

# Creating a trigger for Data Streams that sends messages to WebSocket connections

Create a [trigger for Data Streams](../../concepts/trigger/data-streams-trigger.md) to send messages to [WebSocket connections](../../concepts/extensions/websocket.md) when data is sent to a [stream](../../../data-streams/concepts/glossary.md#stream-concepts).

{% note info %}

The trigger for Data Streams receives and sends messages in [JSON](https://enwikipedia.org/wiki/JSON) format only.

{% endnote %}

## Getting started {#before-you-begin}

To create a trigger, you will need:

* API gateway. Messages will be sent to WebSocket connections accessing the API gateway at the path specified in the trigger settings. If you do not have an API gateway, [create one](../api-gw-create.md).

    {% note info %}

    The trigger does not call the API gateway when sending messages to WebSocket connections.

    {% endnote %}

* [Service account](../../../iam/concepts/users/service-accounts.md) with the `api-gateway.websocketBroadcaster` role. If you do not have a service account, [create one](../../../iam/operations/sa/create.md).

* Stream that will fire the trigger when data is sent to it. If you do not have a stream, [create one](../../../data-streams/quickstart/create-stream.md).

## Creating a trigger {#trigger-create}

{% note info %}

The trigger is initiated within five minutes after it is created.

{% endnote %}

{% list tabs group=instructions %}

- Management console {#console}

    1. In the [management console](https://console.yandex.cloud), select the folder where you want to create a trigger.

    1. Navigate to **API Gateway**.

    1. In the left-hand panel, select ![image](../../../_assets/console-icons/gear-play.svg) **Triggers**.

    1. Click **Create trigger**.

    1. Under **Basic settings**:

        * Enter a name and description for the trigger.
        * In the **Type** field, select `Data Streams`.
        * In the **Launched resource** field, select `API gateway`.

    1. Under **Data Streams settings**, select a data stream and a service account with read and write permissions to the stream.

    1. Optionally, under **Batch message settings**, specify:

        * Message batch size in bytes. The values may range from 1 B to 64 KB. The default value is 1 B.
        * Maximum wait time. The values may range from 1 to 60 seconds. The default value is 1 second.

        The trigger groups messages within the specified wait time period and sends them to WebSocket connections. The total amount of data transmitted to connections may exceed the specified batch size if the data is transmitted as a single message. In all other cases, the amount of data does not exceed the batch size.

    1. Under **API gateway settings**:
       * In the **API gateway** field, select the API gateway.
       * In the **Path** field, specify the path in the OpenAPI specification. Messages will be sent through WebSocket connections established using this path.
       * In the **Service account** field, select the [service account](../../../iam/concepts/users/service-accounts.md) to send messages to WebSocket connections.

    1. Click **Create trigger**.

- CLI {#cli}

    If you do not have the Yandex Cloud CLI yet, [install and initialize it](../../../cli/quickstart.md#install).

    The folder used by default is the one specified when [creating](../../../cli/operations/profile/profile-create.md) the CLI profile. To change the default folder, use the `yc config set folder-id <folder_ID>` command. You can also specify a different folder for any command using `--folder-name` or `--folder-id`. If you access a resource by its name, the search will be limited to the default folder. If you access a resource by its ID, the search will be global, i.e., through all folders based on access permissions.

    To create a trigger that sends messages to WebSocket connections, run this command:

    ```bash
    yc serverless trigger create yds \
      --name <trigger_name> \
      --database <database_location> \
      --stream <data_stream_name> \
      --batch-size 1b \
      --batch-cutoff 1s \
      --stream-service-account-id <service_account_ID> \
      --gateway-id <API_gateway_ID> \
      --gateway-websocket-broadcast-path <path> \
      --gateway-websocket-broadcast-service-account-id <service_account_ID>
    ```

    Where:

    * `--name`: Trigger name.
    * `--database`: Location of the YDB database associated with the stream in Data Streams.

      To find out where the database is located, run the `yc ydb database list` command. The database location is specified in the `ENDPOINT` column, in the `database` property, e.g., `/ru-central1/b1gia87mbah2********/etn7hehf6gh3********`.

    * `--stream`: Stream name.

    * `--batch-size`: Message batch size. This is an optional setting. The values may range from 1 B to 64 KB. The default value is 1 B.

    * `--batch-cutoff`: Maximum wait time. This is an optional setting. The values may range from 1 to 60 seconds. The default value is 1 second. The trigger groups messages within the `batch-cutoff` period and sends them to WebSocket connections. The total amount of data transmitted to connections may exceed `batch-size` if the data is transmitted as a single message. In all other cases, the amount of data does not exceed `batch-size`.

    * `--stream-service-account-id`: ID of the service account with write and read permissions for the stream.

    * `--gateway-id`: API gateway ID.
    * `--gateway-websocket-broadcast-path`: Path in the OpenAPI specification. Messages will be sent through WebSocket connections established using this path.
    * `--gateway-websocket-broadcast-account-id`: Service account ID with permissions to send messages to WebSocket connections.

    Result:

    ```text
    id: a1s5msktijh2********
    folder_id: b1gmit33hgh2********
    created_at: "2022-10-24T14:07:04.693126923Z"
    name: data-streams-trigger
    rule:
      data_stream:
        database: /ru-central1/b1gia87mbah2********/etn7hehh2********
        stream: streams-name
        service_account_id: ajep8qm0kh2********
        batch_settings:
          size: "1"
          cutoff: 1s
        gateway_websocket_broadcast:
          gateway_id: d4eofc7n0mh2********
          path: /
          service_account_id: aje3932acdh2********
    status: ACTIVE
    ```

- API {#api}

  To create a trigger for Data Streams, use the [create](../../triggers/api-ref/Trigger/create.md) REST API method for the [Trigger](../../triggers/api-ref/Trigger/index.md) resource or the [TriggerService/Create](../../triggers/api-ref/grpc/Trigger/create.md) gRPC API call.

{% endlist %}

## Checking the result {#check-result}

Check that the trigger operates correctly. Do it by viewing the [API gateway logs](../api-gw-logs.md) that present information about its incoming requests.

## Useful links {#see-also}

* [Trigger for Data Streams that invokes a Cloud Functions function](../../../functions/operations/trigger/data-streams-trigger-create.md)
* [Trigger for Data Streams that invokes a Serverless Containers container](../../../serverless-containers/operations/data-streams-trigger-create.md)