haproxy deprecated trick suggested
the description for "Http check version" say:
Defaults to "HTTP/1.0" if left blank. Note that the Host field is mandatory in HTTP/1.1, and as a trick, it is possible to pass it after "\r\n" following the version string like this: HTTP/1.1\r\nHost:\ www
but this lead to a Warning
[WARNING] 296/004428 (78254) : parsing [/var/etc/haproxy/haproxy.cfg:67]: 'option httpchk' : hiding headers or body at the end of the version string is deprecated. Please, consider to use 'http-check send' directive instead.