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

# Creating a trigger for Message Queue that sends messages to WebSocket connections

Create a [trigger for a Message Queue message queue](../../concepts/trigger/ymq-trigger.md) to send messages to [WebSocket connections](../../concepts/extensions/websocket.md).

{% note warning %}

* You can only create a trigger for a standard message queue.
* The trigger must be in the same cloud as the queue from which it reads messages.
* You can create only one trigger for each message queue.

{% 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).

* Message queue the trigger will pick up messages from. If you do not have a queue, [create one](../../../message-queue/operations/message-queue-new-queue.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 `Message Queue`.
        * In the **Launched resource** field, select `API gateway`.

    1. Under **Message Queue message settings**, select a message queue and a service account with the permission to read messages from it.

    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 0 to 20 seconds. The default value is 10 seconds.

        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 message-queue \
      --name <trigger_name> \
      --queue <queue_ID> \
      --queue-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> \
      --batch-size <message_batch_size>
      --batch-cutoff <maximum_wait_time>
    ```

    Where:

    * `--name`: Trigger name.
    * `--queue`: Queue ID.

        To find out the queue ID:
        
        1. In the [management console](https://console.yandex.cloud), navigate to the folder containing the queue.
        1. Select **Message Queue**.
        1. Select the queue.
        1. You can see the queue ID under **General information** in the **ARN** field.

    * `--queue-service-account-id`: Service account with permissions to read messages from the queue.

    * `--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.

    * `--batch-size`: Message batch size. This is an optional setting. The values may range from 1 to 1,000. The default value is 1.
    * `--batch-cutoff`: Maximum wait time. This is an optional setting. The values may range from 0 to 20 seconds. The default value is 10 seconds. The trigger groups messages within the `batch-cutoff` period and sends them to WebSocket connections. The number of messages cannot exceed `batch-size`.

    Result:

    ```text
    id: a1s5msktijh2********
    folder_id: b1gmit33hgh2********
    created_at: "2022-10-24T15:19:15.353909857Z"
    name: ymq-trigger
    rule:
      message_queue:
        queue_id: yrn:yc:ymq:ru-central1:b1gmit33ngh2********:my-mq
        service_account_id: bfbqqeo6jkh2********
        batch_settings:
          size: "1"
          cutoff: 10s
        gateway_websocket_broadcast:
          gateway_id: d4eofc7n0mh2********
          path: /
          service_account_id: aje3932acdh2********
    status: ACTIVE
    ```

- API {#api}

  To create a trigger for Message Queue, 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}

{% list tabs %}

- Yandex API Gateway

    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.

- Message Queue

    Check that the number of enqueued messages is decreasing. To do this, view the queue statistics:

   1. In the [management console](https://console.yandex.cloud), navigate to **Message Queue**.
   1. Select the queue for which you created the trigger.
   1. Go to **Monitoring**. Check the **Messages in the queue** chart.

{% endlist %}


## Useful links {#see-also}

* [Trigger for Message Queue that sends messages to a Cloud Functions function](../../../functions/operations/trigger/ymq-trigger-create.md)
* [Trigger for Message Queue that sends messages to a Serverless Containers container](../../../serverless-containers/operations/ymq-trigger-create.md)