Question

I keep getting this error in Apache’s error log:

[client 127.0.0.1] Client sent malformed Host header

exactly every 5 minutes. This happens since we installed Varnish on our server, but I can’t understand why and how to fix it. I even tried to set Apache’s error_log verbosity to debug, but no other useful information is provided. Any idea?

Our Varnish configuration is very basic:

backend default {
     .host = "127.0.0.1";
     .port = "9001";
}

sub vcl_recv {
    remove req.http.X-Forwarded-For;
    set req.http.X-Forwarded-For = client.ip;
}

We have several virtualhost that run on port 9001.

Can anyone tell me more about this error and how to resolve or at least investigate about it?

Answer 1

Varnish performs a health check on your backends which might need to be configured more precisely for Apache to accept it. If this doesn’t solve your problem, try logging the User-Agent header in Apache to find out who is make the malformed request.