docker-compose_swarm.yaml

services:

    # ATTENTION: here we use a replica set with docker SWARM (so dont use docker compose for starting it!)
    # to make both available you must use `docker stack deploy -c docker-compose.yaml myswarm`
    # runs only if a remote worker is attatched!

    fastapi_swarm: # this is the SWARM!!!
        image: 192.168.1.1:5000/fastapi_arm:latest  # this will be eval on build time so 192.168.1.1 must be reachable from the machine (here we use the WIN IP but the portproxy will forward it accordingly)
        hostname: "swarm.{{.Task.Slot}}"  # this replaces the containerID with a meaningfull name
        deploy:
          # replicas: 2  # this deploys 2 replicas of this image in docker swarm
          mode: global   # global means it deploy one container on all workers in the swarm (and on the manager node also)
          placement:  
            constraints:
            - node.role == worker # tells Swarm to run one instance of the service on every worker node, excluding the manager
            # to define by tags which nodes should be used (you must tag them before with `docker node update --label-add target=true <MANAGER_NODE_ID>`)
            # - node.labels.target == true 
          restart_policy:
            condition: on-failure
          endpoint_mode: dnsrr  # This tells Docker Swarm to use DNS Round Robin, which will return each container's IP address as separate entries. Then NGINX will have multiple endpoints to distribute requests across.
        # Exposing Ports is NOT needed with SWARM: internal connectivity works automatically
        networks:
            swarm-net:
              aliases:
                - fastapi_swarm

networks:
    swarm-net:  # this will create an overlay network used by docker swarm
        # external: true   # if you wnat to connect to an existing overlay network
        name: swarm-net  # with this the name of the network is setted
        driver: overlay # for all swarm "overlay" network is recommended (mandatory if multiple node setup)
        attachable: true   # <-- important! Docker allows containers (and the Compose process) to attach to the overlay network, preventing the PermissionDenied error.