Function render 

pub fn render(
    org: &OrgId,
    stack: &str,
    service: &str,
    ips: &[IpAddr],
    extra: Option<&str>,
) -> String

The hosts file for a service: one line per address, sorted, with both the full name and the short <service>.<stack>, then the same two in extra (a project environment, <project>-<env>) when there is one.