503 Service Temporarily Unavailable Error

Hello,

It is possible that the error message you’re receiving is being sent by the Load Balancer. This error response code usually indicates that the server is not ready to handle the request. Check that the server is passing health checks or failing if any, with this CloudWatch metrics for your Application Load Balancer and also check your logs with Access logs for your Application Load Balancer. You will likely find what the issue is by looking to see if there are any event logs, failing health checks, or whether your targets behind the ALB are responding to the requests, or if it doesn’t have registered targets. You can verify that the target group has registered targets by following this article.

You can go ahead and reach out to support as well for further clarifications if needed.