WebSocket subscription not working while using multiple Application Load Balancer

Question

Hi,

We are Using Application Load Balancer for our website, We have configured it as below,

1. Two Client instances ( client-A  and  client-B ) for Front-End
 2. Two Server instances ( server-A  and server-B ) for Back-end
  
If we use 2 instances for the client & **single instance** for the server, then every WebSocket **Subscription is working fine **But if we switch it to 2  instances for clients & **2 instances** for the server, then the **WebSocket subscriptions are not working **at all.

Kindly let us know, Is there any methods available to handle web-socket using Load Balancer on AWS, If yes, then kindly guide us to sort out this issue.

We also want to know, To which instance the WebSocket request is entering and from which instance the response is coming out. So kindly help us.

Thanks in Advance...

Answer

Hi.

Do you have two ALBs for the front end and ALB for the back end? What are the roles of front-end and back-end applications?

When a user accesses the backend ALB from a client, the first thing that comes to mind is a session.
WebSocket is stateful. Try ALB's Sticky Session first.

https://docs.aws.amazon.com/elasticloadbalancing/latest/application/sticky-sessions.html

WebSocket subscription not working while using multiple Application Load Balancer

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