Occasionally we see the following in the Tomcat logs:
SEVERE [ajp-nio-8009-exec-3] org.apache.coyote.ajp.AjpMessage.processHeader Invalid message received with signature 18245
it means that one of internal process has tried calling that port with http protocol. In my case, you got this issue when I use "wget"; it's not support a ajp protocol.
Either you listen to your port on http protocol, or you open another http port where your internal process should call.