Websocket issue - sync server time with javascript time

Question

Hello,  
  
We have implemented API Gateway web socket (with serverless AWS Lambda) and it works well.  However, we have encountered a critical issue explained below and would highly appreciate if anybody can provide a solution / workaround:  
  
- We want to sync server time with client/javascript time and wanted to use web sockets to send timestamp to all connected clients at regular intervals.  However, we found that without an input action from a client, we cannot push data to the clients automatically.  Is this understanding correct?  If yes, is there any workaround for this issue, as we are using serverless architecture with AWS Lambda?  
  
Thanks in advance,  
Krishna

Accepted Answer

Oh, I see. You're asking how to run your Lambda periodically like cron job.  
  
First, you have to use $connect route to store connectionIds to somewhere (e.g. DynamoDB).  
  
There would be multiple ways to execute Lambda periodically, but an easiest way would be using CloudWatch event to trigger your Lambda.  
https://docs.aws.amazon.com/lambda/latest/dg/tutorial-scheduled-events-schedule-expressions.html  
  
Your Lambda function needs to retrieve connectionIds, then iterate to invoke pushToConnection to each connectionId. You may use HTTP/2 streaming to send multiple requests same time.

Answer

You can use @connections API to send a message from your backend service.  
  
https://docs.aws.amazon.com/apigateway/latest/developerguide/apigateway-how-to-call-websocket-api-connections.html  
  
Here is a API in SDKs:  
**Java SDK**  
https://docs.aws.amazon.com/AWSJavaSDK/latest/javadoc/com/amazonaws/services/apigatewaymanagementapi/AmazonApiGatewayManagementApiClient.html#postToConnection-com.amazonaws.services.apigatewaymanagementapi.model.PostToConnectionRequest-  
  
**JavaScript SDK**  
https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/ApiGatewayManagementApi.html#postToConnection-property  
  
Please take a look at an example to use postToConnection (written in JavaScript)  
https://github.com/aws-samples/simple-websockets-chat-app/blob/master/sendmessage/app.js

Answer

Many thanks for your response, we are using PostToConnection method mentioned to respond back when a client request comes in. However the issue is that as we are working with a full server-less architecture using AWS Lambda and we don't have the 'back-end service' to trigger messages from as and when we want.  Does this makes sense, please let us know your comments?

Answer

Hello,   
  
Can anybody please advise on this issue?  
  
Thanks  
  
Edited by: KrishnaMK on Mar 27, 2019 4:05 AM

Answer

Thank you very much jwaataws!!!  I think this is what we were looking for, highly appreciate your quick and great response!!!

Websocket issue - sync server time with javascript time

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