Running specific container on predefined host with docker stack - docker-compose

Question

I have spent lots of time trying to figure out the following scenario but no luck uptil now. so here is the case.
I have 2 machines(machine A with IP 123 and machine B with IP 456), 123 is the manager node and 456 is the worker node.
Now there are 2 services that I would like to run, Service-A on IP-123 and Service-B on IP 456 respectively, for that I am using the following compose file
version: '3.8'
networks:
same-network:
ser1-service:
container_name: ser1-service
image: ser1
networks:
- same-network
ports:
- 9057:7057
entrypoint: ["java","-jar","ser1.jar"]
ser2-service:
container_name: ser2-service
image: ser2
networks:
- same-network
ports:
- 9052:7052
entrypoint: ["java","-jar","ser2.jar"]
Now, when I start it using docker stack deploy, it deploys the services randomly. What I want is, to make sure that every time Service-A should be deployed on IP-123 and Service-B should be deployed on IP 456
Just to add one thing I have downloaded both images on both server. Reason is, in the actual scenario, we have lots of services and lots of hosts and they have hard binding with each other. In addition, I want the images to be downloaded on run time on each worker node.
Any help from anyone would be highly appreciated.

Answer 1

The first issue (make sure services A goes to IP 123) - the closest thing I can suggest is to add a deploy section with placement constraint to your stack file. One of the available placement constraints is by hostname, which may be close enough (though not exactly by ip address). Another viable placement constraint is by node labels (which you add yourself to the nodes).
https://docs.docker.com/compose/compose-file/compose-file-v3/#placement
https://docs.docker.com/engine/reference/commandline/service_create/#specify-service-constraints---constraint
ser1-service:
container_name: ser1-service
image: ser1
...
placement:
constraints: [node.hostname == hostname_of_ip_123]
The second issue I think you're asking about making sure the images are downloaded each time (a bit unsure due to wording though) - I believe you want the "--resolve-image=always" flag on your docker stack deploy command:
https://docs.docker.com/engine/reference/commandline/stack_deploy/
--resolve-image always API 1.30+Swarm
Query the registry to resolve image digest and supported platforms ("always"|"changed"|"never")
docker stack deploy -c your_stack_file.yml --resolve-image=always your_stack_name