Docker Swarm - 扩展容器

Question

I have a Docker swarm Environment with 7 nodes(3 master and 4 Workers) I am trying to Deploy a Container and buy requirement is that at any point of time I need 2 instance of this container running but when I scale this the Container should be deployed to a different node than it is currently running.

Ex: say one instance of the container is running in Node 4 and I scale to scale=2 it should run in any other node except for Node 4.

tried this but no luck:

deploy:
  mode: global
  placement:
    constraints:
      - node.labels.cloud.type == nodesforservice

Answer 1

We solved this issue with deployment preferences configuration (under Placement section). We set up node.labels.worker, on all our worker nodes. We have 3 workers they have node.labels.worker = worker1, node.labels.worker = worker2 and node.labels.worker = worker3 labels set to each of them. On the docker compose side then we configure it:

      placement:
        max_replicas_per_node: 2
        constraints:
          - node.role==worker
        preferences:
          - spread: node.labels.worker

Note this will not FORCE it always on the separate node, but if it is possible it will do so. So it is not hard limit. Beware of that.