Contact UsGet started
© 2025 Direct Cursus Technology L.L.C.

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

Written by
Updated at May 5, 2025

Create a trigger for Data Streams to send messages to WebSocket connections when data is sent to a stream.

Note

The trigger for Data Streams accepts and sends messages in JSON format only.

Getting started

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.

    Note

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

  • Service account with the api-gateway.websocketBroadcaster role. If you do not have a service account, create one.

  • A stream that will activate the trigger as soon as it receives data. If you do not have a stream, create one.

Creating a trigger

Note

The trigger is initiated within 5 minutes of being created.

  1. In the management console, select the folder where you want to create a trigger.

  2. Open API Gateway.

  3. In the left-hand panel, select Triggers.

  4. Click Create trigger.

  5. 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.

  6. Under Data Streams settings, select a data stream and a service account with permissions to read data from the stream and write data to it.

  7. (Optional) 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 for a period not exceeding the specified wait time 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.

  8. 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 to send messages to WebSocket connections.

  9. Click Create trigger.

If you do not have the Yandex Cloud CLI yet, install and initialize it.

The folder specified when creating the CLI profile is used by default. To change the default folder, use the yc config set folder-id <folder_ID> command. You can specify a different folder using the --folder-name or --folder-id parameter.

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

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 DB the Data Streams stream is linked to.

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

  • --stream: Stream name.

  • --batch-size: Message batch size. This is an optional parameter. 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 parameter. The values may range from 1 to 60 seconds. The default value is 1 second. The trigger groups messages for a period not exceeding batch-cutoff 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 permissions to read from the stream and write to it.

  • --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:

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

To create a trigger for Data Streams, use the create REST API method for the Trigger resource or the TriggerService/Create gRPC API call.

Checking the result

Check that the trigger operates correctly. Do it by viewing the API gateway logs that present information about its incoming requests.

See also

Previous
Creating a trigger for budgets
Next
Creating an email trigger