It looks like Shopware's xkey implementation for Varnish (as mentioned here https://developer.shopware.com/docs/guides/hosting/infrastructure/reverse-http-cache.html) requires Varnish to have extra big response headers, at least in one case we experience. If not, we get a "Error 503 Backend fetch failed" message.

The problem was fixed if we increased the header length from 8k to 16k as follows:

varnish> param.set httpresphdr_len 16k
200

varnish> param.show httpresphdr_len
200

httpresphdr_len
Value is: 16k [bytes]
Default is: 8k
Minimum is: 40b

Maximum length of any HTTP backend response header we will allow. The limit is inclusive its continuation lines.

This will likely be repeated on other servers when we go live with this change, and also because Shopware 6.7 will only support Varnish xkey. Is there a way to make the Varnish header length a "hypernode-systemctl settings" feature? Or do you have some other ideas on how to implement this in a standard manner?