HHVM with php7.1-fpm as failover

Hi,

This is my first post here. I know it will automatically install php5.6-fpm as failover for hhvm by using:

ee site create domain.com --wp --hhvm

But I want the failover using php7.1-fpm instead. So what I do are:

ee stack install --php7

And I tried to change it manually to replace php5.6-fpm by php7.1-fpm (copy php5.6-fpm config at /etc/php/5.6/fpm to /etc/php/7.1/fpm ) and I remove the php5.6-fpm service but my wordpress database unable to connect. Any solution how?