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Connect to another host with your docker client, without modifying your local Docker installation

Run commands on remote Docker host

This is how to connect to another host with your docker client, without modifying your local Docker installation or when you don't have a local Docker installation.

Enable Docker Remote API

First be sure to enable the Docker Remote API on the remote host.

This can easily be done with a container.
For HTTP connection use jarkt/docker-remote-api.
For HTTPS connection use kekru/docker-remote-api-tls.

You can also configure the Docker engine to expose the remote API. Read Enable Docker Remote API with TLS client verification for more information.

Download docker client

If you don't have a local Docker installation, you need to download the docker client (= docker cli), which is a simple executable.
And then add it to your PATH variable.

Here are some ways how to get the executable.
You only need one of the steps for you OS, not all:

  • Linux:
    • Either: (Any Linux)
      Download tgz file from download.docker.com/linux/static and unzip it. You only need the docker file, which must be added to your PATH.
      Maybe this script helps downloading it.
      Or just run:
      curl https://download.docker.com/linux/static/stable/x86_64/docker-19.03.8.tgz | tar xvz --directory /tmp && mv -v /tmp/docker/docker /usr/local/bin/docker && chmod +x /usr/local/bin/docker && rm -rf /tmp/docker
    • Or: (Ubuntu/Debian)
      $ apt-get update
      $ apt-get install -y apt-transport-https ca-certificates curl gnupg-agent software-properties-common
      $ curl -fsSL https://download.docker.com/linux/ubuntu/gpg | apt-key add -
      # Verify correct gpg key
      $ apt-key fingerprint 0EBFCD88
      $ add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
      $ apt-get update && apt-get install docker-ce-cli
      From Install using the repository, but I would not recommend it, because there are many steps and much to install in the first steps
    • Or: (Centos)
      $ yum install -y yum-utils
      $ yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
      $ yum install -y docker-ce-cli
  • MacOS:
  • Windows

See also the official installation site and Install Docker Engine from binaries

HTTPS connection configuration

Docker's Remote API client authentication works with certificates.
See Protect the Docker daemon socket or my Enable Docker Remote API with TLS client verification on how to create server and client certificates.

For the following examples copy ca.pem (CA certificate), cert.pem (client certificate) and key.pem (client's private key) in /home/me/docker-tls/ or C:\users\me\docker-tls\.

Connect to remote api

Now we will see some ways on how to connect to a docker remote api.

Set alias (Linux and Mac)

For HTTP connection set the following alias:

alias dockerx="docker -H=your-remote-server.org:2375"

For HTTPS connection set the following alias:

alias dockerx="docker \
  --tlsverify \
  -H=your-remote-server.org:2376 \
  --tlscacert=/home/me/docker-tls/ca.pem \
  --tlscert=/home/me/docker-tls/cert.pem \
  --tlskey=/home/me/docker-tls/key.pem"

Now you can run commands on the remote machine with dockerx instead of docker.

Example:

dockerx ps

Create .bat file (Windows)

Create a file dockerx.bat.
For HTTP connection the content of the bat file should be:

docker -H=your-remote-server.org:2375 %*

For HTTPS connection the content of the bat file should be:

docker ^
  --tlsverify ^
  -H=your-remote-server.org:2376 ^
  --tlscacert=C:\users\me\docker-tls\ca.pem ^
  --tlscert=C:\users\me\docker-tls\cert.pem ^
  --tlskey=C:\users\me\docker-tls\key.pem %*

(If this does not work remove the carets (^) and the line breaks)

Now you can run commands on the remote machine with dockerx.bat instead of docker.

Example:

dockerx.bat ps

Set env var (Linux, Mac, Windows)

You can set environment vars to define the docker remote api that should be connected to.

For HTTP connection

# Linux/Mac
export DOCKER_HOST="tcp://your-remote-server.org:2375"

# Windows Powershell
$env:DOCKER_HOST="tcp://your-remote-server.org:2375"

For HTTPS connection

# Linux/Mac
export DOCKER_TLS_VERIFY="1"
export DOCKER_HOST="tcp://your-remote-server.org:2376"
export DOCKER_CERT_PATH="/home/me/docker-tls"

# Windows Powershell
$env:DOCKER_TLS_VERIFY="1"
$env:DOCKER_HOST="tcp://your-remote-server.org:2376"
$env:DOCKER_CERT_PATH="C:\users\me\docker-tls"

Be sure that your DOCKER_CERT_PATH directory contains the following files:

  • ca.pem (CA certificate)
  • cert.pem (client certificate)
  • key.pem (client's private key)

Now any docker command will run against the remote api

docker ps

Do switch back to local docker, unset the env vars:

# Linux/Mac
unset DOCKER_HOST
unset DOCKER_TLS_VERIFY
unset DOCKER_CERT_PATH

# Windows Powershell
Remove-Item env:DOCKER_HOST
Remove-Item env:DOCKER_TLS_VERIFY
Remove-Item env:DOCKER_CERT_PATH

Reuse SSH connection (Linux, Mac, Windows(?))

If you already added an SSH public key to your remote server, then you can use this ssh credentials for your docker connection, too. You don't need to configure the remote api on the server for this approach.
(Should work on Windows, but I did only test on Linux yet)

Set the env var to a ssh address:

# Linux/Mac
export DOCKER_HOST="ssh://username@your-remote-server.org"

# Windows Powershell
$env:DOCKER_HOST="ssh://username@your-remote-server.org"

Now any docker command will run against the remote api

docker ps

Do switch back to local docker, unset the env vars:

# Linux/Mac
unset DOCKER_HOST

# Windows Powershell
Remove-Item env:DOCKER_HOST

Docker Context (Linux, Mac, Windows)

Since Docker 19.03 there is the docker context command. You can define multiple remote servers and switch between them.

Create a context for HTTPS
(Change paths for Windows)

docker context create example-server \
  --description "connection to example server" \
  --docker "host=tcp://your-remote-server.org:2376, \
     ca=/home/me/docker-tls/ca.pem, \
     cert=/home/me/docker-tls/cert.pem, \
     key=/home/me/docker-tls/key.pem"

(For HTTP connection remove ca, cert and key and switch port to 2375. For SSH connection use ssh address)

Now you can call the remote server with:

docker --context example-server ps

Or choose the context and then all following command will call the remote server

docker context use example-server
docker ps
@Forinil
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Forinil commented May 27, 2021

Hi, thanks for the helpful gist.

Has anything changed or I've missed something. But there is no need to create *.bat file on windows anymore. After setting $env:DOCKER_HOST everything work.

Can someone confirm? (I'm running windows in docker mcr.microsoft.com/windows/servercore:ltsc2019)

There was never any need to create a *.bat file. The purposes of the bat files was to create a separate command for every host, eg. docker ps would show dockerized processes on localhost and dockerx ps would do the same, but for some remote server.

You can absolutely pass appropriate parameters using just environment variables or command line switches, although if you regularly work with multiple Docker daemons I would recommend setting up appropriate contexts as described at the very end of this gist.

@krystofwoldrich
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krystofwoldrich commented May 27, 2021

Hi, thanks for the helpful gist.
Has anything changed or I've missed something. But there is no need to create *.bat file on windows anymore. After setting $env:DOCKER_HOST everything work.
Can someone confirm? (I'm running windows in docker mcr.microsoft.com/windows/servercore:ltsc2019)

There was never any need to create a *.bat file. The purposes of the bat files was to create a separate command for every host, eg. docker ps would show dockerized processes on localhost and dockerx ps would do the same, but for some remote server.

You can absolutely pass appropriate parameters using just environment variables or command line switches, although if you regularly work with multiple Docker daemons I would recommend setting up appropriate contexts as described at the very end of this gist.

Ahhh, thank you for explanation. I’ve missed that.

I’m setting up Windows ServerCore docker image with Docker CLI for use in Gitlab CD/CI. So I think the env will be fine.

@donvogel
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donvogel commented Sep 29, 2021

It would be nice if the SSH-approache is verified for windows.
Since Docker updated ther subscription this would be an accepteable drop-in-replacement for Docker-Desktop on Windows.

Sure, you will need some configuration for WSL2 and Docker-cli, but this would be better then pay for featueres you don't need.

@AlexOdobesteanu
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AlexOdobesteanu commented Mar 11, 2022

Hi, @kekru @kekru
I tried using the dockerx.bat script , but the output that i get is "error during connect: Get "https://remote-api.example.com:2376/v1.24/containers/json": dial tcp: lookup remote-api.example.com: no such host".I have set CERT_HOSTNAME=remote-api.example.com in my docker-compose.yml, before i used the command "docker compose up -d", but now i can't connect to it.So you have any idea what the problem could be?

@kekru
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kekru commented Mar 12, 2022

@AlexOdobesteanu
Did you replace remote-api.example.com with your real domain name? This is only an example, which will not work.

You can try it out with a curl to the url:

$ curl https://remote-api.example.com:2376/v1.24/containers/json
curl: (6) Could not resolve host: remote-api.example.com

If you dont have a real domain name, you could use remote-api.127-0-0-1.nip.io (replace 127-0-0-1 with the IP address of the docker server).
See also https://nip.io

@AlexOdobesteanu
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AlexOdobesteanu commented Mar 12, 2022

@AlexOdobesteanu Did you replace remote-api.example.com with your real domain name? This is only an example, which will not work.

You can try it out with a curl to the url:

$ curl https://remote-api.example.com:2376/v1.24/containers/json
curl: (6) Could not resolve host: remote-api.example.com

If you dont have a real domain name, you could use remote-api.127-0-0-1.nip.io (replace 127-0-0-1 with the IP address of the docker server). See also https://nip.io

@kekru @kekru

I fixed the issue with remote-api.example.com.Now i have another problem.How do i get the ip of the docker server ? And there is also something i don't understand.How am i supposed to use CERT_HOSTNAME=remote-api.x.x.x.x.nip.io(ip address of the docker server) in docker-compose.yml , if i don't know the server ip address ? I think i'm missing something.
Thank you very very much !

@kekru
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kekru commented Mar 14, 2022

@AlexOdobesteanu
You don't know your server's IP address? It's the address of the server, where docker is installed. If you use Docker-Desktop, you can use 127.0.0.1. If you are in another linux machine try running ifconfig or curl ifconfig.me or just google for how to find out your IP address

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