'swarm leave' breaks DNS resolution in a bridge network

[kuzjka]

Description

After leaving a swarm, hostname resolution in standalone containers within a bridge network is broken.

Consider the following docker-compose.yml:

version: "2"

services:
  node-1:
    image: alpine
    networks:
      - test_network
    command: tail -f /dev/null

  node-2:
    image: alpine
    networks:
      - test_network
    command: tail -f /dev/null

networks:
  test_network:
    driver: bridge

Reproduce

1. $ docker compose up -d
2. $ docker compose exec node-1 getent hosts node-2
   172.19.0.2 node-2 node-2
3. $ docker compose exec node-2 getent hosts node-1
   172.19.0.3 node-1 node-1
4. $ docker swarm init
5. $ docker swarm leave --force
6. $ docker compose exec node-1 getent hosts node-2
   (no result)
7. $ docker compose exec node-2 getent hosts node-1
   (no result)
8. $ docker compose exec node-1 ping node-2
   ping: bad address 'node-2'

Expected behavior

• output in steps 6-7 is the same as in steps 2-3
• ping in step 8 is successful

docker version

Client: Docker Engine - Community
 Version:           20.10.17
 API version:       1.41
 Go version:        go1.17.11
 Git commit:        100c701
 Built:             Mon Jun  6 23:02:46 2022
 OS/Arch:           linux/amd64
 Context:           default
 Experimental:      true

Server: Docker Engine - Community
 Engine:
  Version:          20.10.17
  API version:      1.41 (minimum version 1.12)
  Go version:       go1.17.11
  Git commit:       a89b842
  Built:            Mon Jun  6 23:00:51 2022
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.6.6
  GitCommit:        10c12954828e7c7c9b6e0ea9b0c02b01407d3ae1
 runc:
  Version:          1.1.2
  GitCommit:        v1.1.2-0-ga916309
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

docker info

Client:
 Context:    default
 Debug Mode: false
 Plugins:
  app: Docker App (Docker Inc., v0.9.1-beta3)
  buildx: Docker Buildx (Docker Inc., v0.8.2-docker)
  compose: Docker Compose (Docker Inc., v2.6.0)
  scan: Docker Scan (Docker Inc., v0.17.0)

Server:
 Containers: 2
  Running: 2
  Paused: 0
  Stopped: 0
 Images: 51
 Server Version: 20.10.17
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: systemd
 Cgroup Version: 2
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 io.containerd.runtime.v1.linux runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 10c12954828e7c7c9b6e0ea9b0c02b01407d3ae1
 runc version: v1.1.2-0-ga916309
 init version: de40ad0
 Security Options:
  apparmor
  seccomp
   Profile: default
  cgroupns
 Kernel Version: 5.15.0-67-generic
 Operating System: Ubuntu 22.04 LTS
 OSType: linux
 Architecture: x86_64
 CPUs: 1
 Total Memory: 7.764GiB
 Name: kuzjkavm
 ID: FVID:U7VB:TP5U:2UVI:QK2W:3SJD:BE5E:YXS7:HZNY:DP7R:UYL4:2BVO
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 Registry: https://index.docker.io/v1/
 Labels:
 Experimental: false
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false

Additional Info

Hostname resolution is restored after restarting with docker compose restart.

Probably related to #38900, #42877

[ilyzbs]

I also encountered the same problem, how to solve it?

[pduchnovsky]

I also encountered the same problem, how to solve it?

docker compose restart as mentioned in original post, commenting so people see this more clearly :D