AWS API Gateway Web Socket Api - broadcast message to all connected clients

Question

I've created a Web Socket Api using API Gateway and I'm able to connect clients to it.

Also, I'm able to send messages to a connected client by specifying its ConnectionId and using the following code:

const AWS = require('aws-sdk');
let apiGatewayManagementApi = new AWS.ApiGatewayManagementApi({
  apiVersion: '2018-11-29',
  endpoint: 'https://XXXXXXXXX.execute-api.sa-east-1.amazonaws.com/dev/',
  region: 'sa-east-1'
});
const params = {
  ConnectionId: 'YYYYYYYYYYYYY',
  Data: 'test'
};
apiGatewayManagementApi.postToConnection(params, function (err, data) {
  if (err) {
    console.log(err, err.stack); // an error occurred
  } else {
    console.log(data);           // successful response
  }
});

The issue is that I don't have the need for differentiating between clients, and so I don't want to keep track of each client's ConnectionId, but if I remove it while sending a message, I get the following error: Missing required key 'ConnectionId' in params

Is there a way to send a message to all connected clients (without specifying any ConnectionId)?

Answer 1

Unfortunately, you have to specify the ConnectionId. A pattern that I have seen is to persist connection information to DynamoDB on the $connect event; then you could do something like this:

const connections = await getAllConnections();
const promises = connections.map(c => apiGwMgmtApi.postToConnection({ ConnectionId: c.connectionId, Data: 'test' }).promise());
await Promise.all(promises);