With cache

services:
  wms:
    srs: ['EPSG:4326']
    image_formats: ['image/png']

layers:
  - name: persons
    title: Person layer
    sources: [persons_cache]

caches:
  persons_cache:
    grids: [GLOBAL_GEODETIC]
    sources: [persons_wms]
    format: image/png
    request_format: image/png
    disable_storage: true
    meta_size: [4, 4]
    meta_buffer: 256

sources:
  persons_wms:
    type: wms
    wms_opts:
      version: 1.3.0
    forward_req_params: ['key', 'env']
    req:
      url: http://foo.com/mapserver/cgi-bin/mapserv.fcgi?
      layers: persons
      map: /var/maps/persons.map
      supported_srs: ['EPSG:4326']

globals:
  cache:
    meta_size: [4, 4]
    meta_buffer: 256