After docker is shutdown, the worker node  changes its status to Down, but availability remains at Active.

[解决方案]

1. From: https://github.com/moby/moby/issues/23828

   this is a docker issue, rather than a swarmkit issue.

2. From https://forums.docker.com/t/docker-worker-nodes-shown-as-down-after-re-start/22329/4

   Try removing all nodes including manager(for manager:using docker swarm leave --force) from cluster & then again create a cluster with all old nodes.
   your services & all currant state of machines will remain the same.

    

注： 解决方案就是重新加入。如果还不行，就在manager机器上执行swarm leave (--force)来终止整个swarm, 然后重新创建swarm. 如果还有问题，只能重新创建虚机，然后重新创建swarm了。