Docker – How to scale docker swarm dynamically

You can do docker node ls to see all the nodes in your swarm, then docker node ps <node> to see the containers on that node.

As a one liner, you can do:

docker node ps $(docker node ls -q)

Basic template for Docker Swarm with Traefik 2.4, domain-based routing, regular SSL and scalable web-app, all on bare metal servers.

Traefik will be run on all master nodes, directly listening on host's port 0.0.0.0:80 and 0.0.0.0:443. http is upgraded to https, web-apps are started on worker nodes and will be automatically registered with their domain. Then Traefik will load balanced all incoming requests and forward them to the matching worker containers.

Note that this is NOT a failover solution. You need to have a load balancer in front of this setup or a floating IP which you can switch over if a server fails.

Requirements: Setup a docker swarm, this is out of scope here. Every Docker Swarm master node Traefik is running on needs a local folder with the config.yml and SSL certificate. Alternatively you can use a Docker volume, which can be a remote NFS mount.

traefik.yml

version: '3.8'
services:
    traefik:
        image: traefik:v2.4
        ports:
          - target: 80
            published: 80
            protocol: tcp
            mode: host
          - target: 443
            published: 443
            protocol: tcp
            mode: host
        command:
          - --providers.docker.swarmMode=true
          - --providers.docker.exposedByDefault=false
          - --providers.docker.network=proxy
          - --providers.file.filename=/data/traefik/config.yml
          - --providers.file.watch=true
          - --entrypoints.web.address=:80
          - --entrypoints.web.http.redirections.entryPoint.to=websecure
          - --entrypoints.web.http.redirections.entryPoint.scheme=https
          - --entrypoints.websecure.address=:443
          - --accesslog
          - --log.level=info
        environment:
          - TZ=Europe/Berlin
        volumes:
          - /var/run/docker.sock:/var/run/docker.sock:ro
          - /data/traefik:/data/traefik
        networks:
          - proxy
        deploy:
            mode: global
            placement:
                constraints:
                    - node.role == manager
networks:
    proxy:
        external: true

config.yml, volume from local folder, SSL certificate settings NEED to be in a separate file

tls:
    certificates:
      - certFile: /data/traefik/certs/wildcard.crt
        keyFile: /data/traefik/certs/wildcard.key
      - certFile: /data/traefik/certs/another-certificate.crt
        keyFile: /data/traefik/certs/another-certificate.key

    stores:
        default:
        defaultCertificate:
            certFile: /data/traefik/certs/wildcard.crt
            keyFile: /data/traefik/certs/wildcard.key

Command line, start your engines :-)

# create network (just once)
docker network create --driver=overlay proxy

# start traefik via traefic.yml
docker stack deploy --compose-file traefik.yml traefik

# start a web-app with its domain name
docker service create \
  --replicas 15 \
  --name web-app \
  --constraint node.role!=manager \
  --network proxy \
  --label  traefik.enable=true \
  --label 'traefik.http.routers.traefik.rule=Host(`app.doma.in`)' \
  --label  traefik.http.routers.traefik.entrypoints=websecure \
  --label  traefik.http.routers.traefik.tls=true \
  --label  traefik.http.services.hostname.loadbalancer.server.port=80 \
  nginxdemos/hello

You can reduce the log.level (or remove it completely), also the accesslog can be removed. Alternatively it is possible to log those two types into two different files. Traefik dashboard is still missing in this config.

For better security you can use docker-socket-proxy which @webjocky describes in his pastebin in this discussion.