Swarm service port mappings

General
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1

Hi,

My container runs a TCP socket server which listens to commands on port 6000.

Now i launch this same container as a swarm service with multiple replicas.
Somehow, I want all the containers in the service to be able to receive the commands simultaneously at their internal port 6000, when I make a tcp connection from outside.

But when i connect to the host using :6000, only one container at any time receives the commands.

I created the swarm with 2 replicas:

docker service create
–replicas 2
–network mynet
–mount type=bind,source=/tmp/.X11-unix,destination=/tmp/.X11-unix
-p 6000:6000
–name service_nv2
–restart-condition=none
myContainerImage /home/command.sh

I see my 2 containers are launched correctly on the 2 hosts.
But only one of them gets my commands.

2

Hi, this is the normal behavior.
Swarm has an internal load balancer which takes your request and point it to one of the replicas using Round Robin algorithm.

Regards

3

Hi @eldeberde
Thank you for your message.

Do you know if there is any way to influence that internal load-balancer and tell it to forward the message to a particular container with a specific ip-address of the container?

4

Hi. I don’ t know any way.

One possible solution is use other load balancer like https://traefik.io/ and register your replicas when it starts.
It has an API where your containers can register itself, and them you can play with that.

I think you can also use haproxy

Regards