per-hosts_foo.sls

include:
    - softwares.postgresql.server

softwares_postgresql_server.sls

postgresql-server:
    pkg.installed:
        - name: postgresql-9.1
    service:
        - running

## That's what I would like to set
roles:
    grains.append:
        - value: database-server

top.sls

base:
    '*':
        - per-hosts.{{ grains['host'] }}