# Creating a trigger that sends messages to WebSocket connections from a Yandex IoT Core broker topic

Create a [trigger](../../concepts/trigger/iot-core-trigger.md) for a Yandex IoT Core broker topic and send message copies to Yandex API Gateway [WebSocket connections](../../concepts/extensions/websocket.md).

{% note warning %}

The trigger must be in the same cloud as the broker from topic of which it reads messages.

{% endnote %}

## Getting started {#before-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).

* [Broker](../../../iot-core/concepts/index.md#broker) from the topic of which the trigger will collect message copies. If you do not have a broker, [create one](../../../iot-core/operations/broker/broker-create.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 `IoT Core (broker)`.
        * In the **Launched resource** field, select `API gateway`.

    1. Under **IoT Core message settings**:
      
        * In the **Broker** field, specify the broker.
        * Optionally, in the **MQTT topic** field, specify an MQTT topic. If no MQTT topic is set, the trigger will fire for all broker topics.

    1. Under **Batch message settings**, specify:

        * Batch size. The values may range from 1 to 1,000. The default value is 1.
        * 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 number of messages cannot exceed the specified 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 iot-broker \
      --name <trigger_name> \
      --broker-id <broker_ID> \
      --mqtt-topic '<broker_MQTT_topic>' \
      --batch-size <message_batch_size> \
      --batch-cutoff <maximum_wait_time> \
      --gateway-id <API_gateway_ID> \
      --gateway-websocket-broadcast-path <path> \
      --gateway-websocket-broadcast-service-account-id <service_account_ID>
    ```

    Where:

    * `--name`: Trigger name.
    * `--broker-id`: [Broker ID](../../../iot-core/operations/broker/broker-list.md).
    * `--mqtt-topic`: MQTT topic you want to create a trigger for. This is an optional setting. If you skip it, the trigger will fire for all broker topics.

    * `--batch-size`: Message batch size. This is an optional parameter. The values may range from 1 to 10. The default value is 1.
    * `--batch-cutoff`: Maximum wait time. This is an optional parameter. The values may range from 0 to 20 seconds. The default value is 10 seconds. The trigger groups messages for a period not exceeding `batch-cutoff` and sends them to WebSocket connections. The number of messages cannot exceed `batch-size`.

    * `--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: "2022-10-24T15:19:15.353909857Z"
    name: iot-broker-trigger
    rule:
      iot_broker_message:
        broker_id: arenou2oj4h2********
        mqtt_topic: topic-for-broker
        batch_settings:
          size: "1"
          cutoff: 0s
        gateway_websocket_broadcast:
          gateway_id: d4eofc7n0mh2********
          path: /
          service_account_id: aje3932acdh2********
    status: ACTIVE
    ```

- API {#api}

  To create a trigger for Yandex IoT Core, 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.

## See also {#see-also}

* [Trigger for Yandex IoT Core that sends messages from topics to a Cloud Functions function](../../../functions/operations/trigger/iot-core-trigger-broker-create.md)
* [Trigger for Yandex IoT Core that sends messages from topics to a Serverless Containers container](../../../serverless-containers/operations/iot-core-trigger-broker-create.md)