Application load balancer blocks websocket connections?


I made a websocket server on fargate, but I have an connection issue with application load balancer. The server works fine without ALB (with direct access to the IP of the fargate task). But when I access via ALB, it blocks the websocket connection. I enabled the stickiness of the target group. How can we use websocket with ALB?

1 Answer

Check that the client can reach the ALB and that the ALB's security group is configured in your fargate backend.

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answered 4 months ago
  • The security group of the ALB and the service using the ALB is the same one of the fargate service without ALB. What is strange is that the connectivity depends on the client. If I test with wscat, I can connect to the fargate service with ALB. However, if I use other client (for example, minecraft), I cannot connect to it. Of course, I can connect with minecraft to the fargate service without ALB. What is wrong with the ALB?

  • Maybe there is something not standard with the minecraft websocket implementation?

  • But the only difference is ALB. Why ALB does not behave the same as the direct connection? The implementation of the websocket application must take care of the difference?

  • Anyone has any ideas?

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