How do you mount the docker socket on Windows? - docker

Question

I'm trying to make an application work on Windows that's been developed only on Unices. It's all dockerized and it uses the traefik load balancer. The volumes for the docker for running traefik looks like this:
volumes:
- /var/run/docker.sock:/var/run/docker.sock:ro,delegated
- ${PWD}/load_balancer/traefik.toml:/etc/traefik/traefik.toml:ro,delegated
The first volume works fine on Mac or Linux, but does it on Windows? The application is failing (the load balancer is giving a 404) and it might be related to that volume. When I start the image, the socket looks like a socket:
/ # ls -laF /var/run/docker.sock
srw-rw---- 1 root root 0 Sep 2 11:04 /var/run/docker.sock=
Is this working? Any way to test it? What's the correct way of doing this?
Trying to figure this out, I tried replacing it with this:
volumes:
- //./pipe/docker_engine:/var/run/docker.sock
based on various articles and bug reports I found online. The docker image starts but it fails in the same way and now in the docker container it looks like a directory:
/ # ls -laF /var/run/docker.sock
total 4
drwxr-xr-x 2 root root 40 Sep 3 14:52 ./
drwxr-xr-x 1 root root 4096 Sep 3 14:57 ../
Following Marc ABOUCHACRA's answers, I tried:
volumes:
- type: npipe
source: ////./pipe/docker_engine
target: /var/run/docker.sock
consistency: delegated
but that also looks like a directory:
/ # ls -laF /var/run/docker.sock
total 4
drwxr-xr-x 2 root root 40 Sep 3 14:52 ./
drwxr-xr-x 1 root root 4096 Sep 3 14:57 ../
I also tried this:
volumes:
- npipe:////./pipe/docker_engine:/var/run/docker.sock:ro,delegated
but that fails with this error:
ERROR: Volume npipe:////./pipe/docker_engine:/var/run/docker.sock:ro,delegated has incorrect format, should be external:internal[:mode]
The whole docker-compose.yml section looks like this:
lb:
image: load-balancer
build: ${WORKSPACE}/go-home/load_balancer
ports:
- 80:80
- 443:443
links:
- wifi-ui-dev
- wifi-ui-prod
- portal
- wifi-api
env_file:
- .env
volumes:
- /var/run/docker.sock:/var/run/docker.sock:ro,delegated
- ${PWD}/load_balancer/traefik.toml:/etc/traefik/traefik.toml:ro,delegated
My question is specifically about running this docker image, which is a Linux, on a Windows host, running Docker for Windows. I understand that I can run it on a Linux host by installing Linux on another machine or a VM on the Windows machine, it's equivalent. Running Windows guests is not what I'm after either in case there's a way of exposing sockets from Windows to Windows only.

Answer 1

If you cannot nor want use network sockets, then you can use named pipes.
The syntax depends whether you run Linux or Windows containers and on the shell you use.
Linux containers
If you run Linux containers on a Windows machine, this seems to work using Powershell or bash:
docker run --rm -it -v "//var/run/docker.sock://var/run/docker.sock" image_with_docker docker version
Please note the extra / in front of /var/run/docker.sock, both for the source and destination volumes.
Windows containers
If you run Windows containers on a Windows machine, this seems to work using Powershell or bash:
docker run -v "//./pipe/docker_engine://./pipe/docker_engine" --rm -it image-with-docker docker version
Note that this works only in Powershell:
docker run -v "\\.\pipe\docker_engine:\\.\pipe\docker_engine" --rm -it image-with-docker docker version
Therefore, it's better to use the version with /.
Extra - docker-compose.yml
If you use a docker-compose.yaml file, this works with Windows containers.
version: '3.7'
services:
docker:
image: image-with-docker
command:
- docker
- version
volumes:
- type: npipe
source: \\.\pipe\docker_engine
target: \\.\pipe\docker_engine
With Linux containers, you can use the shortened form:
docker:
image: image-with-docker
command:
- docker
- version
volumes:
- //var/run/docker.sock://var/run/docker.sock
Extra - Kubernetes
If you are running Windows containers on a Windows node in Kubernetes, this seems to work:
apiVersion: v1
kind: Pod
spec:
containers:
- name: docker
image: image-with-docker
command:
- powershell
args:
- Start-Sleep
- "999999"
volumeMounts:
- mountPath: \\.\pipe\docker_engine
name: dockersock
volumes:
- name: dockersock
hostPath:
path: \\.\pipe\docker_engine
type: null
nodeSelector:
kubernetes.io/os: windows
In this case, beside using the \, please note the type: null in the definition of the dockersock volume: if you don't set it, it will not work.
Notes
Everything was tested on docker 19.03 and on Kubernetes 1.18.
Client:
Version: 19.03.3
API version: 1.40
Go version: go1.12.10
Git commit: 2355349d-
Built: 10/14/2019 16:41:26
OS/Arch: windows/amd64
Experimental: false
Server: Docker Engine - Community
Engine:
Version: 19.03.8
API version: 1.40 (minimum version 1.24)
Go version: go1.12.17
Git commit: afacb8b
Built: Wed Mar 11 01:37:20 2020
OS/Arch: windows/amd64
Experimental: false

Answer 2

If you encounter the following error on windows:
cannot create container for service portainer: Unrecognised volume spec: file '\.\pipe\docker_engine' cannot be mapped. Only directories can be mapped on this platform
ERROR: Encountered errors while bringing up the project.
Try adding an extra slash to it, resulting in following volumes section:
volumes:
- source: \\.\pipe\docker_engine\
target: \\.\pipe\docker_engine\
type: npipe
Tested with compose 3.7 and docker CE 19.03.12

Answer 3

Using short syntax with the type of the bind mount is not possible : npipe:////./pipe/docker_engine:/var/run/docker.sock:ro,delegated
You need to use the long syntax in your compose file :
volumes:
- type: npipe
source: ////./pipe/docker_engine
target: /var/run/docker.sock
consistency: delegated
You can find some documentation about the long syntax in the official documentation. This syntaxe is from v3.2
Also keep in mind what #lucas-ramage said about using windows container only when using npipe.

Answer 4

In 2022, on Windows 11, what worked for me is below volume configuration (Note the doube slash (//) on the host side of configruation. Not sure why docker_enginer variant does not work for me.
-v "//var/run/docker.sock:/var/run/docker.sock"

Answer 5

Per the Docker for Windows FAQ,
On Docker Desktop for Windows, clients can connect to the Docker Engine through a named pipe: npipe:////./pipe/docker_engine
See also this issue on GitHub,
The windows version of docker doesn't use unix socket (/var/run/docker.sock) but npipe (npipe:////./pipe/docker_engine). So you have either
to switch to linux container which runs docker in a full virtualized linux with unix socket
to pass the npipe instead of the unix socket to the container (windows container only)
to use a network socket (should work with linux and windows container)
However, since this is a Linux container, your options are either A) Run docker in a virtual machine (first choice above), or B) Use a network socket (the third choice).