docker service replicas remain 0/1

Question

I am trying out docker swarm with 1.12 on my Mac. I started 3 VirtualBox VMs, created a swarm cluster of 3 all fine.

docker@redis1:~$ docker node ls 
ID HOSTNAME STATUS AVAILABILITY MANAGER STATUS
2h1m8equ5w5beetbq3go56ebl    redis3  Ready Active 
8xubu8g7pzjvo34qdtqxeqjlj    redis2  Ready Active Reachable 
cbi0lyekxmp0o09j5hx48u7vm *  redis1  Ready Active Leader

However, when I create a service, I see no errors yet replicas always displays 0/1:

docker@redis1:~$ docker service create --replicas 1 --name hello ubuntu:latest /bin/bash
76kvrcvnz6kdhsmzmug6jgnjv
docker@redis1:~$ docker service ls
ID            NAME   REPLICAS  IMAGE          COMMAND
76kvrcvnz6kd  hello  0/1       ubuntu:latest  /bin/bash
docker@redis1:~$ docker ps
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES

What could be the problem? Where do I look for logs? Thanks!

Answer 1

The problem is that your tasks (calling bin/bash) exits quickly since it's not doing anything.

If you look at the tasks for your service, you'll see that one is started and then shutdown within seconds. Another one is then started, shutdown and so on, since you're requested that 1 task be running at all times.

docker service ps hello

If you use ubuntu:latest top for instance, the task will stay up running.