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I have a bunch of swarm containers (now in one single host, but potentially in a multihost system, conforming a multinode swarm). The system is composed of a data server and a set of autonomous workers processing the bits received by the server and ingesting back the results. The input data retrieval and output data ingestion is done with HTTP GET/POST. The server side (data provision and results reception) works, and when tested against a worker running in any host, without Docker, it runs without problem. But I need to place these workers in a Docker swarm.

What I cannot achieve is the communication between the different swarm workers and the external server. My server is running in a host with IP 10.69.180.30, in the port 8080. 

python test-dataserver.py -H 10.69.180.30 -p 8080

After digging in several forums, I tried to create an overlay network with --subnet 10.69.180.0/24, and then launch the service of workers connected to this network in another host. But no way. 

docker network create --driver overlay --subnet 10.69.180.0/24 mynet
docker service create --network mynet --name mysrv --replicas 4 \
                 centos curl http://10.69.180.30:8080/get_task

In this simple example I don't call the worker but just curl to the address of the server and the get_task node. It should return a JSON string with information about the task to be executed. But on the server side I do not get any request.

I'm not a network expert, so I might be missing something trivial... (BTW, I first tried to do the same, but having the server running in the same host, without success.)

Do you know if this setup is possible? I will very much appreciate any hint to make this work...

Thanks in advance!

J C Gonzalez
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1 Answers1

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i would create a overlay network with Dockers default IP Range

docker network create --driver overlay mynet

After this add the external host to the services.

docker service create 
       --add-host external:10.69.180.30 \
       --network mynet --name mysrv --replicas 4 \
       centos curl http://external:8080/get_task
opHASnoNAME
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  • But, does swarm create command allow `--add-host` option? I thought it was only available for _traditional_ containers. At least it does not work in my system... – J C Gonzalez Oct 20 '17 at 09:43
  • Definitely, it does work! I mean, if I modify the image so that the `/etc/hosts` file contains the IP of the server, the communication is established! Now, I would like to achieve the same but without having to tune the image of the containers... – J C Gonzalez Oct 20 '17 at 10:00