[Docker swarm mode] No round robin when using service

[vincentlepot]

What I tried

docker network create -d overlay frontend

docker service create --name traefik --network frontend -p 8081:8080 -p 81:80 --mount type=bind,src=/var/run/docker.sock,dst=/var/run/docker.sock traefik:camembert --web --docker.swarmmode=true --docker.domain=swarm.test --logLevel=DEBUG

docker service create --name whoami --replicas 5 --label traefik.port=80 --network frontend emilevauge/whoami

But every time I run:

curl -H 'Host: whoami.swarm.test:81' http://x.y.z.t:81/

I have the same container responding (instead of seeing different container ids).

That's strange since this should be distributed by docker itself...

[vincentlepot]

EDIT: It seems like it switches to another container if no activity occurs. Is there a keep-alive between Traefik and the backend or something equivalent?

[vdemeester]

@vincentlepot This is kinda to be expected. Træfik in swarmmode points to the virtual ip of the swarm and thus, let the docker swarm mode internal load balancer work. So it really depends on how the swarm mode load balancer handle these.

[mvdstam]

Possibly related to moby/moby#25325

[vincentlepot]

The strange thing is that when using another reverse proxy - Interlock for instance - I don't have the issue with the same setup.

[vincentlepot]

@mvdstam Does not really look the same since I don't have any error, just staying on requesting the same container. The other ones are untouched.
It is as if a connection is settled on a container and remains opened. Is there a way to tell Traefik not to use persistent connections on the backends in this case?

[bgv]

In this particular example the emilevauge/whoami http server sets Keep-Alive due to the default settings in Go HTTP server which is 30 seconds, so if you try to refresh in 31s it switches to another instance.

For me it looks that traefik obeys that which i'd not classify as bug. More of a feature which might need on/off configuration switch?

@vincentlepot try this (from Docker demos):

docker service create --name vote --replicas 5 --label traefik.port=80 --network frontend instavote/vote

and it does the balancing on every request.

[vincentlepot]

I agree with you, this is not a bug, more a configuration switch request.

[vincentlepot]

Moreover, that sounds like a client side issue, not a traefik one. Hence, I close this one.