docker swarm . Run some service only once per node - docker

Question

I use docker version
Client:
Version: 18.06.1-ce
API version: 1.38
Go version: go1.10.3
Git commit: e68fc7a
Built: Tue Aug 21 17:24:51 2018
OS/Arch: linux/amd64
Experimental: false
Server:
Engine:
Version: 18.06.1-ce
API version: 1.38 (minimum version 1.12)
Go version: go1.10.3
Git commit: e68fc7a
Built: Tue Aug 21 17:23:15 2018
OS/Arch: linux/amd64
Experimental: false
And docker-compose for configuring my services. I want to have 3 replicas of a server that run on some specially labeled 3 nodes. For this I use yaml configuration like :
version: '3.7'
services:
ser:
deploy:
placement:
constraints:
- "node.labels.cloud.type == nodesforservice"
replicas: 3
restart_policy:
condition: any
rollback_config:
delay: 0s
parallelism: 0
update_config:
delay: 6s
parallelism: 1
environment:
- affinity:service!=stackname_servicename
image: service:latest
and deploy this configuration via
docker stack deploy --compose-file docker-stack.yml stackname
But I have found out that affinity:service!=stackname_servicename does not work properly ( or does not work at all ). It works only in the deprecated standalone mode. If there are only 2 nodes currently available the service will be deployed to some node twice. And it is what I try to avoid.
Is there is any possibility in a docker swarm explicitly say that 2 containers of the same service are not alowed ? I have found only posibility to create global services with --mode global but I need only 3 instances and not more.

Answer 1

if you are using docker create service, you can use --replicas-max-per-node 1 to enforce 1:1 relationship between container and node.
if you are using compose file you can declare max_replicas_per_node under:
deploy:
placement:
max_replicas_per_node: 1
if you need further control on which node can run the container using label, place the label matching at constraint block under placement.
More details here: Compose and Docker compatibility matrix

Answer 2

This is a rather old thread, but using a node label as placement constraint in combination with global mode deployment does the trick.
deploy:
mode: global
placement:
constraints:
- node.labels.cloud.type == nodesforservice
Of course the node label "cloud.type=nodesforservice" needs to be applied to the desired number of nodes.
For Docker swarm there is no such thing as affinity.