@4checkervn

It depends on which version of Varnish you’ve installed & configured.

Try changing:

backend default {
    .host = "127.0.0.1";
    .port = "8080";
}

backend mysite2 {
    .host = "127.0.0.1";
    .port = "8080";
}

sub vcl_recv {
    if (req.http.host == "mysite1.com" || req.http.host == "www.mysite1.com") {
        set req.backend = default;
    } elsif (req.http.host == "mysite2.com" || req.http.host == "www.mysite2.com") {
        set req.backend = mysite2;
    }
}

To:

Varnish 3.x

backend default {
    .host = "127.0.0.1";
    .port = "8080";
}

sub vcl_recv {
    if (req.http.host ~ "^(www\.)?mysite1\.com$") {
        set req.backend = default;
    }

    if (req.http.host ~ "^(www\.)?mysite2\.com$") {
        set req.backend = default;
    }
}

Varnish 4.x

backend default {
    .host = "127.0.0.1";
    .port = "8080";
}

sub vcl_recv {
    if (req.http.host ~ "^(www\.)?mysite1\.com$") {
        set req.backend_hint = default;
    }

    if (req.http.host ~ "^(www\.)?mysite2\.com$") {
        set req.backend_hint = default;
    }
}

… and then restart Varnish.

The above using a regex to match the request instead of using ||. Keeps it short and sweet and only requires that you change mysite# inside the regex.