index.js

const AWS = require('aws-sdk');
const ddb = new AWS.DynamoDB.DocumentClient();
require('./patch.js');
let send = undefined;

function init(event) {
  console.log(event);
  const apigwManagementApi = new AWS.ApiGatewayManagementApi({
    apiVersion: '2018-11-29',
    endpoint: event.requestContext.domainName + '/' + event.requestContext.stage
  });
  send = async(connectionId, data) => {
    await apigwManagementApi.postToConnection({ ConnectionId: connectionId, Data: `Echo: ${data}` }).promise();
  };
}
exports.handler = (event, context, callback) => {
  init(event);
  let message = JSON.parse(event.body).message;
  getConnections().then((data) => {
    console.log(data.Items);
    data.Items.forEach(function(connection) {
      console.log("Connection " + connection.connectionid);
      send(connection.connectionid, message);
    });
  });
  return {};
};

function getConnections() {
  return ddb.scan({ TableName: 'dl_telemetry', }).promise();
}

patch.js

require('aws-sdk/lib/node_loader');
var AWS = require('aws-sdk/lib/core');
var Service = AWS.Service;
var apiLoader = AWS.apiLoader;
apiLoader.services['apigatewaymanagementapi'] = {};
AWS.ApiGatewayManagementApi = Service.defineService('apigatewaymanagementapi', ['2018-11-29']);
Object.defineProperty(apiLoader.services['apigatewaymanagementapi'], '2018-11-29', {
  get: function get() {
    var model = {
      "metadata": {
        "apiVersion": "2018-11-29",
        "endpointPrefix": "execute-api",
        "signingName": "execute-api",
        "serviceFullName": "AmazonApiGatewayManagementApi",
        "serviceId": "ApiGatewayManagementApi",
        "protocol": "rest-json",
        "jsonVersion": "1.1",
        "uid": "apigatewaymanagementapi-2018-11-29",
        "signatureVersion": "v4"
      },
      "operations": {
        "PostToConnection": {
          "http": {
            "requestUri": "/@connections/{connectionId}",
            "responseCode": 200
          },
          "input": {
            "type": "structure",
            "members": {
              "Data": { "type": "blob" },
              "ConnectionId": {
                "location": "uri",
                "locationName": "connectionId"
              }
            },
            "required": ["ConnectionId", "Data"],
            "payload": "Data"
          }
        }
      },
      "shapes": {}
    }
    model.paginators = { "pagination": {} }
    return model;
  },
  enumerable: true,
  configurable: true
});
module.exports = AWS.ApiGatewayManagementApi;