docker compose file not working: replicas Additional property replicas is not allowed

Indentation is critical in docker-compose.yml. The way you have it set up, “deploy” is a service, which is not intended. The deploy section is intended to specify information about how the “web” service should be deployed. The following allows docker-compose up and docker stack deploy web --compose-file docker-compose.yml to run successfully for me:

version: "3"

services:
  web:
    image: tuhina/friendlyhello:2.0
    deploy:
      replicas: 5
      resources:
        limits:
          cpus: "0.1"
          memory: '50M'
      restart_policy:
        condition: on-failure
    ports:
      - "80:80"
    networks:
      - webnet

networks:
  webnet: