/etc/salt/master:

file_roots:
  base:
    - /opt/salt/base/
  Staging:
    - /opt/salt/Staging/

pillar_roots:
  base:
    - /opt/salt/pillar/base
runner_roots:
  base:
    -/opt/salt/runners

nodegroups:
  server-group: 'L@server1.domain.tld,server2.domain.tld'

salt -N server-group returns with hosts expected.

/opt/salt/base/top.sls:

base:
  '*':
    - salt
  'server-group':
      - match: nodegroup
      - collect_netstat_error
  'virtual: physical':
      - match: grain
      - sysstat