hybrid swarm (linux plus windows) bind mounting fails depending on platform of leader

[dazinator]

Description

Given:

• You have a swarm with windows and linux nodes - sometimes referred to as "hybrid swarm"
• Each node has an SMB file share mapped:
  • to x:/ on windows nodes
  • to /x on linux nodes
  • Note: using a file share to replicate this issue may not actually be necessary but its what I tested with.

Then when the leader is a linux node
You can't docker stack deploy a stack with a windows container that bind mounts from x:/ - the swarm complains its an invalid source path for the bind mount.
Yet you can deploy a stack with a linux container that bind mounts from /x successfully.
It doesn't matter if you execute the docker stack deploy command on a windows manager node or a linux manager node, whilst the leader is a linux node, bind mounting of windows paths like x:/ will fail.
If you force the leader to be a windows node (i.e by demoting / promoting), you can now successfully docker stack deploy the windows container image that bind mounts from x:/ however now you are in a position where you can't deploy linux containers that bind mount from /x.

The result is, if you want to use windows and linux containers, that both bind mount from SMB file shares mounted on them, your deployment routine has to force an appropriate leader before attempting the docker stack deploy - which is not very great as it shouldn't matter what the leader is, and having to force a new leader for a deplyment means demoting all managers except the one you want to lead which obviously is not good!

Describe the results you received:
You can see much more detail about the results I received and the test I ran originally before I knew the leader effected the outcome. See this: #34997 (comment)

Describe the results you expected:
I expected to be able to deploy windows containers and linux containers to the swarm, where both can successfully bind mount from the host they are placed on, irrespective of whether the leader is linux or windows platform.

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

Output of docker version:

Client:
 Cloud integration: 1.0.17
 Version:           20.10.8
 API version:       1.41
 Go version:        go1.16.6
 Git commit:        3967b7d
 Built:             Fri Jul 30 19:58:50 2021
 OS/Arch:           windows/amd64
 Context:           default
 Experimental:      true

Server: Docker Engine - Community
 Engine:
  Version:          20.10.8
  API version:      1.41 (minimum version 1.24)
  Go version:       go1.16.6
  Git commit:       75249d8
  Built:            Fri Jul 30 19:54:29 2021
  OS/Arch:          windows/amd64
  Experimental:     true

Output of docker info:

Client:
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Build with BuildKit (Docker Inc., v0.6.1-docker)
  compose: Docker Compose (Docker Inc., v2.0.0-rc.2)
  scan: Docker Scan (Docker Inc., v0.8.0)

Server:
 Containers: 0
  Running: 0
  Paused: 0
  Stopped: 0
 Images: 1
 Server Version: 20.10.8
 Storage Driver: windowsfilter (windows) lcow (linux)
  Windows:
  LCOW:
 Logging Driver: json-file
 Plugins:
  Volume: local
  Network: ics internal l2bridge l2tunnel nat null overlay private transparent
  Log: awslogs etwlogs fluentd gcplogs gelf json-file local logentries splunk syslog
 Swarm: active
  NodeID: w6gts6jf44gdgcjfwko57ssan
  Is Manager: true
  ClusterID: chlz13kcglzuozrpbbu4oddrf
  Managers: 1
  Nodes: 3
  Default Address Pool: 10.0.0.0/8
  SubnetSize: 24
  Data Path Port: 4789
  Orchestration:
   Task History Retention Limit: 5
  Raft:
   Snapshot Interval: 10000
   Number of Old Snapshots to Retain: 0
   Heartbeat Tick: 1
   Election Tick: 10
  Dispatcher:
   Heartbeat Period: 5 seconds
  CA Configuration:
   Expiry Duration: 3 months
   Force Rotate: 0
  Autolock Managers: false
  Root Rotation In Progress: false
  Node Address: 10.1.0.4
  Manager Addresses:
   10.1.0.4:2377
 Default Isolation: hyperv
 Kernel Version: 10.0 19043 (19041.1.amd64fre.vb_release.191206-1406)
 Operating System: Windows 10 Pro Version 2009 (OS Build 19043.1165)
 OSType: windows
 Architecture: x86_64
 CPUs: 2
 Total Memory: 8GiB
 Name: swarm-1
 ID: MKGD:LP7S:4Z3O:4UYA:RI4M:DRIE:OGUA:QKOK:MWJJ:JK6O:CELC:WVRW
 Docker Root Dir: C:\ProgramData\Docker
 Debug Mode: false
 Registry: https://index.docker.io/v1/
 Labels:
 Experimental: true
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false
 Product License: Community Engine

Additional environment details (AWS, VirtualBox, physical, etc.):