default.vcl

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

backend node1 {
    .host = "127.0.0.1";
    .port = "3000";
}

backend node2 {
    .host = "127.0.0.1";
    .port = "3001";
}

sub vcl_recv {
    if (req.http.Upgrade ~ "(?i)websocket") {
       if (req.http.host ~ "domain1.com") {
           set req.backend = node1;
        } else if (req.http.host ~ "domain2.com") {
           set req.backend = node2;
       }

       return(pipe);
    } else {
      set req.backend = nginx;
    }
}

sub vcl_pipe {
    if (req.http.upgrade) {
      set bereq.http.upgrade = req.http.upgrade;
    }
}