Debian Varnish 6.x Modules (xkey included)
You can configure Varnish daemon by following env variables:
VCL_CONFIG
/etc/varnish/default.vcl
CACHE_SIZE256M
VARNISHD_PARAMS-p default_ttl=3600 -p default_grace=3600 -p max_esi_depth=15 -p feature=+esi_disable_xml_check