cap env files refer to www-data webserver group, but there is no group on the web machines

[halkyon]

cat /etc/group | grep sites on rep1, no result.

But the cap file for this environment references sites as a webserver group, e.g, currently it has the following user and group:

set :webserver_group, "sites"
set :webserver_user, "www-data"

This needs to be updated to either create the group on the machines, or use an alternative one in the env files.