docker service replicas remain 0/1 - docker

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.

Answer 2

This also can happen if you specify a volume in your compose file that is bound to a local directory that does not exist.
If you look at the log (on some Linux systems, this is journalctl -xe), you'll see which volume can't be bound.

Answer 3

In my case, the replicas were not working and a 0/0 was shown as I did not build them before.
As I saw here, when u publish to swarm with a
docker-compose.yml you need to build them before
So, I decided to do a full system prune, and next to it, a build and a deploy (here, my stack was called demo and I did not have previous services or containers running):
docker stack rm demo
docker system prune --all
docker-compose build
docker stack deploy -c ./docker-compose.yml demo
After this, all was up and running and now services replicas are up on swarm
PS C:\Users\Alejandro\demo> docker service ls
ID NAME MODE REPLICAS IMAGE PORTS
oi0ngcmv0v29 demo_appweb replicated 2/2 webapp:1.0 *:80->4200/tcp
ahuyj0idz5tv demo_express replicated 2/2 backend:1.0 *:3000->3000/tcp
fll3m9p6qyof demo_fileinspector replicated 1/1 fileinspector:1.0 *:8080->8080/tcp
The way I maintain the replicas working, at the moment, in dev mode:
Angular/CLi app:
command: >
bash -c "npm install && ng serve --host 0.0.0.0 --port 4200"
NodeJS Backend (Express)
command: >
bash -c "npm install && set DEBUG=myapp:* & npm start --host 0.0.0.0 --port 3000"