API Gateway Websockets not sending to all clients - websocket

Question

I'm using websockets with API Gateway and dynamoDB to maintain all connection IDs.
What I'm trying to do is when a new message comes in, a message is sent to all connected clients.
For example, inside the $default route a message will be received from the client. I'm then querying dynamo to get all connected ids and sending that message.
Querying dynamo:
const params = {
TableName: process.env.CONNECTIONS_TABLE,
IndexName: process.env.CONNECTIONS_COMPANY_INDEX,
KeyConditionExpression: "company = :company",
ExpressionAttributeValues: {
":company": data.company,
},
};
const response = await dynamodb.query(params).promise();
response.Items.forEach(async (item) => {
try {
await apig
.postToConnection({
ConnectionId: item.connectionId,
Data: JSON.stringify(data),
})
.promise();
} catch (e) {
if (e.statusCode === 410) {
console.log(e)
}
}
});
The issue I'm having is that it's only received on the clients after the second attempt. So the client sends a message "123" (the above code is run successfully and I've verified it's getting all connections, no errors) but nothing is received by the client. The client sends another message - "456", now both clients will receive the "123" message.
Any ideas why this would happen? I'd expect that each message sent, would receive the same message to all connected clients, not delayed and always one behind.
Thank you!

Answer 1

i faced with exact same issue. Then i just Remove integration response from the API gateway and leave the function return {}
https://docs.aws.amazon.com/apigateway/latest/developerguide/apigateway-websocket-api-routes-integrations.html#apigateway-websocket-api-overview-integrations-differences
In the HTTP protocol, in which requests and responses are sent
synchronously; communication is essentially one-way. In the WebSocket
protocol, communication is two-way. Responses are asynchronous and are
not necessarily received by the client in the same order as the
client's messages were sent. In addition, the backend can send
messages to the client.