Docker Swarm - strategy doesn't seem to have any effect - docker

Question

I have provisioned a swarm master and swarm nodes with Docker Machine (as described here). Everything is working fine; all the machines are created and running, they have all been discovered and accepts containers.
The output from 'docker-machine ls' is:
$ docker-machine ls
NAME ACTIVE DRIVER STATE URL SWARM DOCKER ERRORS
default - virtualbox Stopped Unknown
local - virtualbox Stopped Unknown
my-swarm * (swarm) digitalocean Running tcp://104.131.161.197:2376 my-swarm (master) v1.11.1
node0 - digitalocean Running tcp://104.236.29.169:2376 my-swarm v1.11.1
node1 - digitalocean Running tcp://104.236.216.164:2376 my-swarm v1.11.1
The problem I'm having is with the distribution of containers. No matter which strategy I set for the swarm, it only seems to distribute containers to one of the nodes at a time. I.e. I run a bunch of containers, and the are all started on the same node, as shown below (with strategy Spread):
$ docker ps
5c075d7ccddc stress "/bin/sh -c /stress.s" 32 seconds ago Up 31 seconds node0/elated_goldstine
5bae22a15829 stress "/bin/sh -c /stress.s" 46 seconds ago Up 44 seconds node0/cocky_booth
dc52b3dfa0e6 stress "/bin/sh -c /stress.s" About a minute ago Up About a minute node0/goofy_kalam
3b9e69c694da stress "/bin/sh -c /stress.s" About a minute ago Up About a minute node0/focused_fermat
ef0e006ff3e0 stress "/bin/sh -c /stress.s" About a minute ago Up About a minute node0/stoic_engelbart
53e46b19ab33 stress "/bin/sh -c /stress.s" About a minute ago Up About a minute node0/condescending_rosalind
e9e126c7f4c6 stress "/bin/sh -c /stress.s" About a minute ago Up About a minute node0/sleepy_jang
f9c0003d509d stress "/bin/sh -c /stress.s" About a minute ago Up About a minute node0/amazing_bhaskara
What I would expect here is for the containers to be distributed roughly evenly on the 3 nodes, especially as the script I'm running in the containers is designed to take as much CPU as possible. But instead all of them are on node0 (which I would only expect with Binpack). The Random strategy has the exact same behaviour.
The output from 'docker info' with the swarm master set as active seems correct:
$ docker info
Containers: 15
Running: 4
Paused: 0
Stopped: 11
Images: 5
Server Version: swarm/1.2.1
Role: primary
Strategy: spread
Filters: health, port, containerslots, dependency, affinity, constraint
Nodes: 3
my-swarm: 104.131.161.197:2376
└ ID: L2HK:F6S3:WWIM:BHNI:M4XL:KLEA:4U22:J6CE:ZHZI:OGGT:76KF:MTQU
└ Status: Healthy
└ Containers: 2
└ Reserved CPUs: 0 / 1
└ Reserved Memory: 0 B / 513.4 MiB
└ Labels: executiondriver=, kernelversion=4.2.0-27-generic, operatingsystem=Ubuntu 15.10, provider=digitalocean, storagedriver=aufs
└ Error: (none)
└ UpdatedAt: 2016-05-09T10:25:24Z
└ ServerVersion: 1.11.1
node0: 104.236.29.169:2376
└ ID: I3TQ:5BMS:TM2P:GLL4:64OH:BDMY:SWBU:3QG4:TOZ2:LEDW:A6SQ:X34H
└ Status: Healthy
└ Containers: 12
└ Reserved CPUs: 0 / 1
└ Reserved Memory: 0 B / 513.4 MiB
└ Labels: executiondriver=, kernelversion=4.2.0-27-generic, operatingsystem=Ubuntu 15.10, provider=digitalocean, storagedriver=aufs
└ Error: (none)
└ UpdatedAt: 2016-05-09T10:25:02Z
└ ServerVersion: 1.11.1
node1: 104.236.216.164:2376
└ ID: OTQH:UBSV:2HKE:ZVHL:2K7Z:BYGC:ZX25:Y6BQ:BN5J:UWEB:65KE:DABM
└ Status: Healthy
└ Containers: 1
└ Reserved CPUs: 0 / 1
└ Reserved Memory: 0 B / 513.4 MiB
└ Labels: executiondriver=, kernelversion=4.2.0-27-generic, operatingsystem=Ubuntu 15.10, provider=digitalocean, storagedriver=aufs
└ Error: (none)
└ UpdatedAt: 2016-05-09T10:25:10Z
└ ServerVersion: 1.11.1
Plugins:
Volume:
Network:
Kernel Version: 4.2.0-27-generic
Operating System: linux
Architecture: amd64
CPUs: 3
Total Memory: 1.504 GiB
Name: my-swarm
Docker Root Dir:
Debug mode (client): false
Debug mode (server): false
WARNING: No kernel memory limit support
Is there some piece I have missed that is necessary for this type of automatic distribution to work the way I'm expecting?

Answer 1

Issue
It is most likely that you Docker Agent does not have the image you try to run on them.
Note that swarm build and swarm pull will not build, or pull, on each Docker agent.
Solution A
Run the pull manually on each Docker Agent
Solution B (not tested)
Run a local Docker registry wherein the Docker agent will pull the images from.
Have fun with Swarm! Also, if I may, I suggest you to read this answer that details a whole step-by-step tutorial on Swarm.