sub vcl_deliver {
    # Happens when we have all the pieces we need, and are about to send the
    # response to the client.

    if (resp.status == 503) {
        set resp.http.failing-backend = "true";
    }

    # Give some debug
    if (req.http.X-debug && req.esi_level == 0) {
        set resp.http.X-Backend = req.backend_hint;
        set resp.http.X-Backend-Url = req.url;
    } else {
        # not debug, strip some headers
        unset resp.http.X-Cache;
        unset resp.http.X-Backend;
        unset resp.http.x-upstream;
        unset resp.http.x-request-uri;
        unset resp.http.Via;
        unset resp.http.xkey;
        unset resp.http.x-goog-hash;
        unset resp.http.x-goog-generation;
        unset resp.http.X-GUploader-UploadID;
        unset resp.http.x-goog-storage-class;
        unset resp.http.x-goog-metageneration;
        unset resp.http.x-goog-stored-content-length;
        unset resp.http.x-goog-stored-content-encoding;
        unset resp.http.x-goog-meta-goog-reserved-file-mtime;
        unset resp.http.Server;
        unset resp.http.X-Apache-Host;
        unset resp.http.X-Varnish-Backend;
        unset resp.http.X-Varnish-Host;
        unset resp.http.X-Nginx-Host;
        unset resp.http.X-Upstream-Age;
        unset resp.http.X-Retries;
        unset resp.http.X-TTL;
        unset resp.http.X-Varnish;
    }
}