hostname in /etc/hosts disappears when --publish option is used for a service in Docker Swarm

[fabrizio2210]

Description
When I deploy an image as a service in a Docker Swarm environment, the /etc/hosts of the container is populated in different manner. I found that the hostname of the container is not added when I use --publish PORT option.

I build this image to test: fabrizio2210/test-hostname:latest
This is is the Dockerfile:

FROM arm32v7/busybox
COPY script.sh  script.sh
CMD [ "./script.sh"]

And this is the content of the script.sh:

#!/bin/sh

cat /etc/hosts 
while true; do
sleep 5
done

Steps to reproduce the issue:

1. Deploy the service using this command:
   docker service create --name test fabrizio2210/test-hostname:latest
2. Check output of the container or enter in the container to "cat" the /etc/hosts
   You can see the couple IP of the container and hostname like:
   172.17.0.2 a3108c5bfefb
3. Deploy the same service with the published port:
   docker service create --name test --publish 80 fabrizio2210/test-hostname:latest
4. Check output of the container or enter in the container to "cat" the /etc/hosts
   There is no hostname in /etc/hosts except for localhost

Describe the results you received:

pi@raspberrypi0:~ $ docker container logs cf0c51d01a9b
127.0.0.1       localhost
::1     localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

Describe the results you expected:

pi@raspberrypi0:~ $ docker container logs a3108c5bfefb
127.0.0.1       localhost
::1     localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
172.17.0.2      a3108c5bfefb

Additional information you deem important (e.g. issue happens only occasionally):
The issue always happens

Output of docker version:

pi@raspberrypi0:~ $ docker version
Client:
 Version:       17.12.1-ce
 API version:   1.35
 Go version:    go1.9.4
 Git commit:    7390fc6
 Built: Tue Feb 27 22:25:15 2018
 OS/Arch:       linux/arm

Server:
 Engine:
  Version:      17.12.1-ce
  API version:  1.35 (minimum version 1.12)
  Go version:   go1.9.4
  Git commit:   7390fc6
  Built:        Tue Feb 27 22:21:21 2018
  OS/Arch:      linux/arm
  Experimental: false

Output of docker info:

pi@raspberrypi0:~ $ docker info
Containers: 20
 Running: 3
 Paused: 0
 Stopped: 17
Images: 68
Server Version: 17.12.1-ce
Storage Driver: overlay2
 Backing Filesystem: extfs
 Supports d_type: true
 Native Overlay Diff: true
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
 Volume: local
 Network: bridge host macvlan null overlay
 Log: awslogs fluentd gcplogs gelf journald json-file logentries splunk syslog
Swarm: active
 NodeID: y15gvi6g5o50zu2q3qzo2eq6c
 Is Manager: true
 ClusterID: kx4saemliu20kljbbxb4kh1pq
 Managers: 2
 Nodes: 2
 Orchestration:
  Task History Retention Limit: 5
 Raft:
  Snapshot Interval: 10000
  Number of Old Snapshots to Retain: 0
  Heartbeat Tick: 1
  Election Tick: 3
 Dispatcher:
  Heartbeat Period: 5 seconds
 CA Configuration:
  Expiry Duration: 3 months
  Force Rotate: 0
 Autolock Managers: false
 Root Rotation In Progress: false
 Node Address: 192.168.4.10
 Manager Addresses:
  192.168.4.10:2377
  192.168.4.11:2377
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: 9b55aab90508bd389d7654c4baf173a981477d55
runc version: 9f9c96235cc97674e935002fc3d78361b696a69e
init version: 949e6fa
Security Options:
 seccomp
  Profile: default
Kernel Version: 4.9.59-v7+
Operating System: Raspbian GNU/Linux 9 (stretch)
OSType: linux
Architecture: armv7l
CPUs: 4
Total Memory: 927.3MiB
Name: raspberrypi0.oss
ID: OKJL:ZBK7:WL6R:EDZN:25NF:JK5X:KPPP:7SKK:O4LQ:CVKK:SKID:6INB
Docker Root Dir: /var/lib/docker
Debug Mode (client): false
Debug Mode (server): false
Username: fabrizio2210
Registry: https://index.docker.io/v1/
Labels:
Experimental: false
Insecure Registries:
 127.0.0.0/8
Live Restore Enabled: false

WARNING: No memory limit support
WARNING: No swap limit support
WARNING: No kernel memory limit support
WARNING: No oom kill disable support
WARNING: No cpu cfs quota support
WARNING: No cpu cfs period support

Additional environment details (AWS, VirtualBox, physical, etc.):
The environment is on raspberry pi 3