moby: Swarm worker cannot connect to master if proxy is configured

Description

Beginning with Docker CE 17.09, a Swarm worker connects to its master through a configured proxy. Unfortunately this fails because Docker stores the master IP addresses instead of hostnames so the master doesn’t match the values configured in NO_PROXY.

Steps to reproduce the issue:

1. Setup Docker as usual. Add a proxy configuration like this to /etc/systemd/system/docker.service.d/proxy.conf:

   [Service]
   Environment="HTTP_PROXY=http://proxy.internal.company.com:8080" "HTTPS_PROXY=http://proxy.internal.company.com:8080" "NO_PROXY=localhost,127.0.0.1,.internal.company.com"
   

   Don’t forget to systemctl daemon-reload and restart the Docker daemon.

2. Initialize swarm on the master node

   master# docker swarm init
   Swarm initialized: current node (0tf92vjqqivr9mujdd99ip6ob) is now a manager.
   
   To add a worker to this swarm, run the following command:
   
       docker swarm join --token SWMTKN-1-20n86wgp1jlfdku52x5pzlcwc6youavmzm78junqe7wtxqg4t5-2orbo6etiiknwjcfj8g52chtr 192.168.1.11:2377
   
   To add a manager to this swarm, run 'docker swarm join-token manager' and follow the instructions.
   

3. Add a worker as indicated:

   worker# docker swarm join --token SWMTKN-1-20n86wgp1jlfdku52x5pzlcwc6youavmzm78junqe7wtxqg4t5-2orbo6etiiknwjcfj8g52chtr 192.168.1.11:2377
   

   Swarm join hangs because docker attempts to connect to the master through the proxy. Then it reports

   Error response from daemon: rpc error: code = Unavailable desc = grpc: the connection is unavailable
   

   Repeat with a FQDN and the join succeeds right away:

   # docker swarm join --token SWMTKN-1-20n86wgp1jlfdku52x5pzlcwc6youavmzm78junqe7wtxqg4t5-2orbo6etiiknwjcfj8g52chtr master.internal.company.com:2377
   This node joined a swarm as a worker.
   

   However, after a dockerd restart the worker canot connect to a master again.

Describe the results you received: See above.

Describe the results you expected: A swarm worker should either ignore the proxy settings, store the master FQDN instead of IP address, or have an option whether to use the proxy for master connections.

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

Output of docker version:

# docker version
Client:
 Version:      17.09.0-ce
 API version:  1.32
 Go version:   go1.8.3
 Git commit:   afdb6d4
 Built:        Tue Sep 26 22:41:23 2017
 OS/Arch:      linux/amd64

Server:
 Version:      17.09.0-ce
 API version:  1.32 (minimum version 1.12)
 Go version:   go1.8.3
 Git commit:   afdb6d4
 Built:        Tue Sep 26 22:42:49 2017
 OS/Arch:      linux/amd64
 Experimental: false

Output of docker info:

Containers: 0
 Running: 0
 Paused: 0
 Stopped: 0
Images: 0
Server Version: 17.09.0-ce
Storage Driver: zfs
 Zpool: error while getting pool information strconv.ParseUint: parsing "": invalid syntax
 Zpool Health: not available
 Parent Dataset: apppool/docker
 Space Used By Parent: 405504
 Space Available: 20671299584
 Parent Quota: no
 Compression: lz4
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: 6c839q9vfo18ucl8g7yykwukg
 Is Manager: false
 Node Address: 192.168.1.12
 Manager Addresses:
  192.168.1.11:2377
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: 06b9cb35161009dcb7123345749fef02f7cea8e0
runc version: 3f2f8b84a77f73d38244dd690525642a72156c64
init version: 949e6fa
Security Options:
 seccomp
  Profile: default
Kernel Version: 3.10.0-693.5.2.el7.x86_64
Operating System: Red Hat Enterprise Linux Server 7.4 (Maipo)
OSType: linux
Architecture: x86_64
CPUs: 8
Total Memory: 39.12GiB
Name: worker
ID: PLND:NJOE:YUR6:XJLP:HYEM:IO4I:KS4G:5BYP:ZOOD:BEJH:G2FR:4VVE
Docker Root Dir: /var/lib/docker
Debug Mode (client): false
Debug Mode (server): false
Http Proxy: http://proxy.internal.company.com:8080
Https Proxy: http://proxy.internal.company.com:8080
No Proxy: localhost,127.0.0.1,.internal.company.com
Registry: https://index.docker.io/v1/
Experimental: false
Insecure Registries:
 127.0.0.0/8
Live Restore Enabled: false

Additional environment details (AWS, VirtualBox, physical, etc.): OS is RHEL 7.4 running on vSphere 6.5