Fix empty IP for backend when dnsrr in Docker swarm mode

[caseycs]

Do you want to request a feature or report a bug?

I'd like to report a bug.

What did you do?

I made a fresh ubuntu setup, applied the last updates(apt-get update && apt dist-upgrade):

ubuntu@ubuntu-xenial:~$ lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 16.04.3 LTS
Release:	16.04
Codename:	xenial
ubuntu@ubuntu-xenial:~$ uname -a
Linux ubuntu-xenial 4.4.0-38-generic #57-Ubuntu SMP Tue Sep 6 15:42:33 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

Then I installed latest docker:

ubuntu@ubuntu-xenial:~$ docker --version
Docker version 17.12.0-ce, build c97c6d6

And configured it to swarm mode:

sudo docker swarm init

Started 4 instances of simple service:

sudo docker service create --name nginx \
  --endpoint-mode dnsrr \
  --label traefik.frontend.rule=Host:test.test.nl \
  --label traefik.port=80 \
  nginx:alpine \
  && sudo docker service scale nginx=4

Downloaded last traefik release binary - 1.5.2.

Made a config file:

debug = true
[entryPoints]
    [entryPoints.http]
    address = ":80"

[docker]
endpoint = "unix:///var/run/docker.sock"
watch = true
swarmmode = true

Then I run traefik:

ubuntu@ubuntu-xenial:~$ sudo ./traefik_linux-amd64 -c traefik.toml
INFO[2018-02-16T10:23:10Z] Using TOML configuration file /home/ubuntu/traefik.toml
INFO[2018-02-16T10:23:10Z] Traefik version v1.5.2 built on 2018-02-12_10:56:31AM

What did you expect to see?

I expected to see correct container ip addresses as backend endpoints.

What did you see instead?

Creating server server-nginx-1 at http://:80

...
DEBU[2018-02-16T10:23:10Z] Configuration received from provider docker: {"backends":{"backend-nginx":{"servers":{"server-nginx-1":{"url":"http://:80","weight":0},"server-nginx-2":{"url":"http://:80","weight":0},"server-nginx-3":{"url":"http://:80","weight":0},"server-nginx-4":{"url":"http://:80","weight":0}},"loadBalancer":{"method":"wrr"}}},"frontends":{"frontend-Host-test-test-nl-0":{"entryPoints":["http"],"backend":"backend-nginx","routes":{"route-frontend-Host-test-test-nl-0":{"rule":"Host:test.test.nl"}},"passHostHeader":true,"priority":0,"basicAuth":[]}}}
DEBU[2018-02-16T10:23:10Z] Creating frontend frontend-Host-test-test-nl-0
DEBU[2018-02-16T10:23:10Z] Wiring frontend frontend-Host-test-test-nl-0 to entryPoint http
DEBU[2018-02-16T10:23:10Z] Creating route route-frontend-Host-test-test-nl-0 Host:test.test.nl
DEBU[2018-02-16T10:23:10Z] Creating backend backend-nginx
DEBU[2018-02-16T10:23:10Z] Creating load-balancer wrr
DEBU[2018-02-16T10:23:10Z] Creating server server-nginx-1 at http://:80 with weight 0
DEBU[2018-02-16T10:23:10Z] Creating server server-nginx-2 at http://:80 with weight 0
DEBU[2018-02-16T10:23:10Z] Creating server server-nginx-3 at http://:80 with weight 0
DEBU[2018-02-16T10:23:10Z] Creating server server-nginx-4 at http://:80 with weight 0...

Output of traefik version: (What version of Traefik are you using?)

ubuntu@ubuntu-xenial:~$ ./traefik_linux-amd64 version
Version:      v1.5.2
Codename:     cancoillotte
Go version:   go1.9.4
Built:        2018-02-12_10:56:31AM
OS/Arch:      linux/amd64

What is your environment & configuration (arguments, toml, provider, platform, ...)?

debug = true
[entryPoints]
    [entryPoints.http]
    address = ":80"

[docker]
endpoint = "unix:///var/run/docker.sock"
watch = true
swarmmode = true

If applicable, please paste the log output in debug mode (--debug switch)

ubuntu@ubuntu-xenial:~$ sudo ./traefik_linux-amd64 -c traefik.toml  --debug
INFO[2018-02-16T10:25:27Z] Using TOML configuration file /home/ubuntu/traefik.toml
INFO[2018-02-16T10:25:27Z] Traefik version v1.5.2 built on 2018-02-12_10:56:31AM
INFO[2018-02-16T10:25:27Z]
Stats collection is disabled.
Help us improve Traefik by turning this feature on :)
More details on: https://docs.traefik.io/basics/#collected-data

DEBU[2018-02-16T10:25:27Z] Global configuration loaded {"LifeCycle":{"RequestAcceptGraceTimeout":0,"GraceTimeOut":0},"GraceTimeOut":0,"Debug":true,"CheckNewVersion":true,"SendAnonymousUsage":false,"AccessLogsFile":"","AccessLog":null,"TraefikLogsFile":"","TraefikLog":null,"LogLevel":"DEBUG","EntryPoints":{"http":{"Network":"","Address":":80","TLS":null,"Redirect":null,"Auth":null,"WhitelistSourceRange":null,"Compress":false,"ProxyProtocol":null,"ForwardedHeaders":{"Insecure":true,"TrustedIPs":null}}},"Cluster":null,"Constraints":[],"ACME":null,"DefaultEntryPoints":["http"],"ProvidersThrottleDuration":2000000000,"MaxIdleConnsPerHost":200,"IdleTimeout":0,"InsecureSkipVerify":false,"RootCAs":null,"Retry":null,"HealthCheck":{"Interval":30000000000},"RespondingTimeouts":null,"ForwardingTimeouts":null,"Web":null,"Docker":{"Watch":true,"Filename":"","Constraints":null,"Trace":false,"DebugLogGeneratedTemplate":false,"Endpoint":"unix:///var/run/docker.sock","Domain":"","TLS":null,"ExposedByDefault":true,"UseBindPortIP":false,"SwarmMode":true},"File":null,"Marathon":null,"Consul":null,"ConsulCatalog":null,"Etcd":null,"Zookeeper":null,"Boltdb":null,"Kubernetes":null,"Mesos":null,"Eureka":null,"ECS":null,"Rancher":null,"DynamoDB":null,"ServiceFabric":null,"Rest":null,"API":null,"Metrics":null,"Ping":null}
INFO[2018-02-16T10:25:27Z] Preparing server http &{Network: Address::80 TLS:<nil> Redirect:<nil> Auth:<nil> WhitelistSourceRange:[] Compress:false ProxyProtocol:<nil> ForwardedHeaders:0xc420606e00} with readTimeout=0s writeTimeout=0s idleTimeout=3m0s
INFO[2018-02-16T10:25:27Z] Starting provider *docker.Provider {"Watch":true,"Filename":"","Constraints":null,"Trace":false,"DebugLogGeneratedTemplate":false,"Endpoint":"unix:///var/run/docker.sock","Domain":"","TLS":null,"ExposedByDefault":true,"UseBindPortIP":false,"SwarmMode":true}
INFO[2018-02-16T10:25:27Z] Starting server on :80
DEBU[2018-02-16T10:25:27Z] Provider connection established with docker 17.12.0-ce (API 1.35)
DEBU[2018-02-16T10:25:27Z] Could not load traefik.frontend.whitelistSourceRange labels
DEBU[2018-02-16T10:25:27Z] Could not load traefik.frontend.entryPoints labels
DEBU[2018-02-16T10:25:27Z] Could not load traefik.frontend.auth.basic labels
DEBU[2018-02-16T10:25:27Z] Validation of load balancer method for backend backend-nginx failed: invalid load-balancing method ''. Using default method wrr.
DEBU[2018-02-16T10:25:27Z] Configuration received from provider docker: {"backends":{"backend-nginx":{"servers":{"server-nginx-1":{"url":"http://:80","weight":0},"server-nginx-2":{"url":"http://:80","weight":0},"server-nginx-3":{"url":"http://:80","weight":0},"server-nginx-4":{"url":"http://:80","weight":0}},"loadBalancer":{"method":"wrr"}}},"frontends":{"frontend-Host-test-test-nl-0":{"entryPoints":["http"],"backend":"backend-nginx","routes":{"route-frontend-Host-test-test-nl-0":{"rule":"Host:test.test.nl"}},"passHostHeader":true,"priority":0,"basicAuth":[]}}}
DEBU[2018-02-16T10:25:27Z] Creating frontend frontend-Host-test-test-nl-0
DEBU[2018-02-16T10:25:27Z] Wiring frontend frontend-Host-test-test-nl-0 to entryPoint http
DEBU[2018-02-16T10:25:27Z] Creating route route-frontend-Host-test-test-nl-0 Host:test.test.nl
DEBU[2018-02-16T10:25:27Z] Creating backend backend-nginx
DEBU[2018-02-16T10:25:27Z] Creating load-balancer wrr
DEBU[2018-02-16T10:25:27Z] Creating server server-nginx-3 at http://:80 with weight 0
DEBU[2018-02-16T10:25:27Z] Creating server server-nginx-4 at http://:80 with weight 0
DEBU[2018-02-16T10:25:27Z] Creating server server-nginx-1 at http://:80 with weight 0
DEBU[2018-02-16T10:25:27Z] Creating server server-nginx-2 at http://:80 with weight 0
INFO[2018-02-16T10:25:27Z] Server configuration reloaded on :80
^CINFO[2018-02-16T10:25:27Z] I have to go... interrupt
INFO[2018-02-16T10:25:27Z] Stopping server gracefully
DEBU[2018-02-16T10:25:27Z] Waiting 0s seconds before killing connections on entrypoint http...
DEBU[2018-02-16T10:25:27Z] Entrypoint http closed
INFO[2018-02-16T10:25:27Z] Server stopped
INFO[2018-02-16T10:25:27Z] Shutting down

[traefiker]

Closed by #2887.