Swarm nodes became Drain


We have services running on Docker Swarm:

$ docker --version
Docker version 17.09.0-ce, build afdb6d4

There are one Manager node and three Workers (QA environment).
Suddenly - every node became in “Drain” status:

$ docker node ls
ID                            HOSTNAME              STATUS              AVAILABILITY        MANAGER STATUS
1tjrynfa1jl86e35clgd222s9     hzwzatr7dzxp4000000   Ready               Drain               
ai3040vw51jch7zikcx0mjy5c *   hzwzatr7dzxp4000000   Ready               Drain               Leader
2m498rtdvl49enbz9luf96xfz     hzwzatr7dzxp4000001   Ready               Drain               
sgd2si6637x14nemgrvoyhnlq     hzwzatr7dzxp4000002   Ready               Drain

I fixed this with docker node update --availability active <Node_id>, but can see nothing in logs - why that happen?

There was no any upgrades or something else, just service deployments with docker stack deploy -c docker-compose.yml jm_website --with-registry-auth.