gistfile1.txt

master.d/reactor.conf
reactor:
  - 'salt/states/base/nginx_update':
    - srv/salt/reactor/stop.sls
  
.sls file event
disable_server_in_LB:
  event:
    - wait
    - name: salt/states/base/nginx_update
    - data:
        id: {{ salt['grains.get']('host') }}
    - watch:
      - service: nginx

stop.sls that is run from above event ( cmd to run on LB)
disable server in haproxy:
  local.cmd.run:
    - tgt: LB
    - arg: 
      - echo "disable server here/salt-minion1" | socat stdio /var/lib/haproxy/stats