HTTP/1.1 503 Service Unavailable: Back-end server is at capacity
Content-Length: 0
Connection: keep-alive

AWS ELB2.0

HTTP/1.1 400 Bad Request
Server: awselb/2.0
Date: Sat, 13 Apr 2024 07:11:02 GMT
Content-Type: text/html
Content-Length: 622
Connection: close