Add to haproxy config:
  log /sidecar/log local0
docker-compose.yml:
version: '2'
services:
  haproxy:
    image: haproxy:latest
    volumes_from:
      - syslog-sidecar
  syslog-sidecar:
    image: outstand/syslog-ng-stdout:latestversion: '3.0'
services:
  haproxy:
    image: haproxy:latest
    volumes:
      - syslog:/sidecar
    depends_on:
      - syslog-sidecar
  syslog-sidecar:
    image: outstand/syslog-ng-stdout:latest
    volumes:
      - syslog:/sidecar
volumes:
  syslog: