We have a containerized app stack using laravel 5.6, nginx, redis, supervisor and mysql.

docker-compose.yml

version: '2'

services:
  # Database service
  db:
    image: 'mysql:5.7.22'
    environment:
      - MYSQL_ROOT_PASSWORD=root
      - MYSQL_DATABASE=root
    volumes:
      - './database:/var/lib/mysql'
    ports:
      - '3309:3306'
    networks:
      - mysql_net

  # Cache service
  redis:
    image: 'redis:alpine'
    command: 'redis-server --requirepass password'
    volumes:
      - './redis:/data'
    networks:
      - redis_net

  # API Source Code
  php:
    image: ...
    volumes:
      - './src:/srv/src'
    networks:
      - nginx_net
      - mysql_net
      - redis_net
    depends_on:
      - db
      - redis

  # SUPERVISOR Queue worker
  queue:
    image: ...
    volumes:
      - './src:/srv/src'
    networks:
      - mysql_net
      - redis_net
    depends_on:
      - db
      - redis

  # CRON Task Scheduler
  cron:
    image: ...
    volumes:
      - './src:/srv/src'
    networks:
      - redis_net
      - mysql_net
    depends_on:
      - db

  # NGINX Web Server
  web:
    image: ...
    volumes:
      - './src:/srv/src'
    ports:
      - '88:80'
    networks:
      - nginx_net
    depends_on:
      - php

networks:
  nginx_net:
    driver: bridge
  mysql_net:
    driver: bridge
  redis_net:
    driver: bridge

The cron service only handles the processing of the scheduled tasks

Problem

$schedule->command('email:notifications specific_time')
                ->everyMinute()
                ->withoutOverlapping(2)
                ->onOneServer();

The above task simply runs a query to check if there were any new items were imported and triggers an email to the user, which gets queued.

When scaling the cron service to multiple instances the task runs on all instances and the user receives as many emails as there are instances.

According to the Laravel documentation chaining the onOneServer() method on the scheduler tasks should prevent this behaviour. This is not the case for us, any help will be appreciated.