AWS ELB Apache2 503 Service Unavailable: Back-end Server Is At Capacity
Answer : Solution 1: You will get a "Back-end server is at capacity" when the ELB load balancer performs its health checks and receives a "page not found" (or other simple error) due to a mis-configuration (typically with the NameVirtual host). Try grepping the log files folder using the "ELB-HealthChecker" user agent. e.g. grep ELB-HealthChecker /var/log/httpd/* This will typically give you a 4x or 5x error which is easily fixed. e.g. Flooding, MaxClients etc is giving the problem way too much credit. FYI Amazon: Why not show the returned response from request? Even a status code would help. Solution 2: I just ran into this issue myself. The Amazon ELB will return this error if there are no healthy instances. Our sites were misconfigured, so the ELB healthcheck was failing, which caused the ELB to take the two servers out of rotation. With zero healthy sites, the ELB returned 503 Service Unavailable: Back-end server is at capacity. Solu...