Enable TCP port 2375 for external connection to Docker

docker-api-port.md

Enable TCP port 2375 for external connection to Docker

See this issue.
Docker best practise to Control and configure Docker with systemd.

1. Create daemon.json file in /etc/docker:

    {"hosts": ["tcp://0.0.0.0:2375", "unix:///var/run/docker.sock"]}
   

2. Add /etc/systemd/system/docker.service.d/override.conf

    [Service]
    ExecStart=
    ExecStart=/usr/bin/dockerd
   

3. Reload the systemd daemon:

    systemctl daemon-reload
   

4. Restart docker:

    systemctl restart docker.service
   

This something I've tried as well and ran in to a few issues creating /etc/systemd/system/docker.service.d/override.conf, I am running Debian 10 and installed (and updated) docker using the script provided in the documentation. (Install using the convenience script)

After reloading the systemd daemon docker still failed to start, going to the log I noticed the following line: (getting the last few lines of the log sudo tail -n 100 /var/log/daemon.log

Oct  8 16:40:16 docker-host systemd[1]: Starting Docker Application Container Engine...
Oct  8 16:40:16 docker-host dockerd[675]: unable to configure the Docker daemon with file /etc/docker/daemon.json: the following directives are specified both as a flag and in the configuration file: hosts: (fro
m flag: [fd://], from file: [tcp://0.0.0.0:2375 unix:///var/run/docker.sock])
Oct  8 16:40:16 docker-host systemd[1]: docker.service: Main process exited, code=exited, status=1/FAILURE
Oct  8 16:40:16 docker-host systemd[1]: docker.service: Failed with result 'exit-code'.
Oct  8 16:40:16 docker-host systemd[1]: Failed to start Docker Application Container Engine.
Oct  8 16:40:18 docker-host systemd[1]: docker.service: Service RestartSec=2s expired, scheduling restart.
Oct  8 16:40:18 docker-host systemd[1]: docker.service: Scheduled restart job, restart counter is at 2.
Oct  8 16:40:18 docker-host systemd[1]: Stopped Docker Application Container Engine.

To get this to work I adding hosts to /etc/docker/daemon.json and editing /lib/systemd/system/docker.service (running sudo systemctl status docker.service reported the daemon being loaded from there) where I removed host provided in the start:

# Replacing this line:
ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

# With this line:
ExecStart=/usr/bin/dockerd --containerd=/run/containerd/containerd.sock

After which reloading the systemd daemon and restarting docker worked as a charm.

works great on Ubuntu 20.04 too thanks. Had to reboot the server though as only restarting docker.service did not work

This something I've tried as well and ran in to a few issues creating /etc/systemd/system/docker.service.d/override.conf, I am running Debian 10 and installed (and updated) docker using the script provided in the documentation. (Install using the convenience script)

After reloading the systemd daemon docker still failed to start, going to the log I noticed the following line: (getting the last few lines of the log sudo tail -n 100 /var/log/daemon.log

Oct  8 16:40:16 docker-host systemd[1]: Starting Docker Application Container Engine...
Oct  8 16:40:16 docker-host dockerd[675]: unable to configure the Docker daemon with file /etc/docker/daemon.json: the following directives are specified both as a flag and in the configuration file: hosts: (fro
m flag: [fd://], from file: [tcp://0.0.0.0:2375 unix:///var/run/docker.sock])
Oct  8 16:40:16 docker-host systemd[1]: docker.service: Main process exited, code=exited, status=1/FAILURE
Oct  8 16:40:16 docker-host systemd[1]: docker.service: Failed with result 'exit-code'.
Oct  8 16:40:16 docker-host systemd[1]: Failed to start Docker Application Container Engine.
Oct  8 16:40:18 docker-host systemd[1]: docker.service: Service RestartSec=2s expired, scheduling restart.
Oct  8 16:40:18 docker-host systemd[1]: docker.service: Scheduled restart job, restart counter is at 2.
Oct  8 16:40:18 docker-host systemd[1]: Stopped Docker Application Container Engine.

To get this to work I adding hosts to /etc/docker/daemon.json and editing /lib/systemd/system/docker.service (running sudo systemctl status docker.service reported the daemon being loaded from there) where I removed host provided in the start:

# Replacing this line:
ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

# With this line:
ExecStart=/usr/bin/dockerd --containerd=/run/containerd/containerd.sock

After which reloading the systemd daemon and restarting docker worked as a charm.

Worked for Debian 10, thanks a lot 👍

Server side seems OK but I cant connect to the daemon from other machine:

C:\Users\Plus>docker -H tcp://192.168.3.2:2375 images
error during connect: Get https://192.168.3.2:2375/v1.40/images/json: http: server gave HTTP response to HTTPS client

I can get image list from browser with HTTP but I cannot use Docker Client (CLI) to access it

http://192.168.3.2:2375/v1.40/images/json

Can I force my Docker Client to NOT using HTTPS?
the docker environment is inside a private network so it maybe safe to not using SSL/HTTPS

If you are on mac you can just edit it in Docker -> Preferences -> Docker Engine (just add hosts and press apply & restart)
But if you are lucky and that gives you "Bad request" you can try editing in ~/.docker/daemon.json, that worked for me

Thanks a lot! Centos 7.8

thanks.

Working on Manjaro 20.2.1 :)

You can connect over ssh without having to reconfigure dockerd.

$ docker ps
Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?
$ uname -a
Darwin danielh-mac 20.6.0 Darwin Kernel Version 20.6.0: Wed Jun 23 00:26:31 PDT 2021; root:xnu-7195.141.2~5/RELEASE_X86_64 x86_64
$ export DOCKER_HOST=ssh://example-host
$ docker ps
CONTAINER ID   IMAGE         COMMAND                 CREATED        STATUS       PORTS                                      NAMES
4bbc34bc14dc   mariadb:10.6  "docker-entrypoint.s…"  32 hours ago   Up 32 hours  0.0.0.0:3306->3306/tcp, :::3306->3306/tcp  mariadb
$ ssh example-host uname -a
Linux example-host 5.4.0-80-generic #90-Ubuntu SMP Fri Jul 9 22:49:44 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

Great works for me

Thanks a lot! "Raspbian GNU/Linux 10 (buster)"

I really want to thank you for posting this. Worked great!

thanks

thank you !

Thank you

Thank you!

Worked like charm on centos 7 too. Was struggling to get this working since 2 days.

Steps followed:

1. vi /usr/lib/systemd/system/docker.service

add the line below where you find ExecStart (under Service section):

2. ExecStart=/usr/bin/dockerd -H tcp://0.0.0.0:4243 -H unix:///var/run/docker.sock

Then,
3. systemctl daemon-reload
4. systemctl restart docker.service

Can confirm it works both on arch and debian 11.
Thanks!

I was also unable to get it to work on Debian 11 without the workaround in https://gist.github.com/styblope/dc55e0ad2a9848f2cc3307d4819d819f#gistcomment-3482239 (directly editing the docker.service file). It seems that on Debian 11, the docker.service.d/override.conf doesn't actually get read, so you just have to edit the docker.service.

I also used ExecStart=/usr/sbin/dockerd --containerd=/run/containerd/containerd.sock --tls=false to avoid the very strong and important complaints:

Binding to IP address without --tlsverify is insecure and gives root access on this machine to everyone who has access to your network. host="tcp://0.0.0.0:2375".
Binding to an IP address, even on localhost, can also give access to scripts run in a browser. Be safe out there! host="tcp://0.0.0.0:2375"
Binding to an IP address without --tlsverify is deprecated. Startup is intentionally being slowed down to show this message host="tcp://0.0.0.0:2375"
Please consider generating tls certificates with client validation to prevent exposing unauthenticated root access to your network host="tcp://0.0.0.0:2375"
You can override this by explicitly specifying '--tls=false' or '--tlsverify=false' host="tcp://0.0.0.0:2375"
Support for listening on TCP without authentication or explicit intent to run without authentication will be removed in the next release host="tcp://0.0.0.0:2375"

I absolutely do not get this run with docker 20.10.12 and ubuntu 21.10

I tried to edit /usr/lib/systemd/system/docker.service or do it via systemctl edit docker.service
Every time when I add -H tcp://127.0.0.1:2375 or tcp://0.0.0.0:2375 the docker.service cannot start
I tried with -H unix, without, with --containerd and without.

ExecStart=/usr/bin/dockerd -H tcp://0.0.0.0:2375 -H unix:///var/run/docker.sock --containerd=/run/containerd/containerd.sock

Any suggestion how to solve it?

check logs, journalctl -xe. The options overlap, remove the 127.0.0.1 , 0.0.0.0 means all interfaces.

Follow this:
https://docs.docker.com/engine/install/linux-postinstall/#configure-where-the-docker-daemon-listens-for-connections

NOTE: Just change the IP from 127.0.0.1 to 0.0.0.0 and its work fine for Ubuntu ( for selenium dynamic grid)

I found that the docker daemon failed to start on reboot (only) with the approach described here. I never tracked down the source of the problem.

However, it did lead me to implement instead an alternative solution with socat:

exec socat -d TCP-LISTEN:2375,fork UNIX-CONNECT:/var/run/docker.sock

Notes:

• I used daemontools to launch this an keep it running (https://cr.yp.to/daemontools.html).
• You can protect the port with the range=... option to socat, or with IP tables or netfilter.

Does not work for Docker Desktop on Windows. It refuses bind to 0.0.0.0

I was having an issue to connect from another machine, turns out it was a firewall issue.
to fix I did:
ufw allow 2375/tcp
ufw reload
hopefully this helps someone.

Thanks!!

👍 ✔️ 🙇‍♀️
I can also confirm this, very much GG @styblope, my rock star hero!1 :))))))

Specs:

• Linux Mint 20.3 Una x64
• Docker version 20.10.16, build aa7e414
• Docker Compose version v2.5.0

🔥

I need to run docker from external docker client but the docker server is containerized (no daemon)
is it aplicable ?

I need to run docker from external docker client but the docker server is containerized (no daemon) is it aplicable ?

AFAIK, Docker will be run as daemon wherever you deploy it.

Here's another way that worked for me:

/etc/systemd/system/docker.service.d/override.conf

[Service]
 ExecStart=
 ExecStart=/usr/bin/dockerd --config-file /etc/docker/daemon.json

/etc/docker/daemon.json

{
  "hosts": ["tcp://0.0.0.0:2375", "unix:///var/run/docker.sock"]
}

Thanks! for me it required a reboot to work

AFAIK, Docker will be run as daemon wherever you deploy it.

Docker in Docker has two versions

• docker:latest daemond and host dependant
• docker:dind web interface based (seems to be no daemon | or fully isolated from host)

I was testing docker, minikube, and K8s functionalities inside docker

The way I was able to do that without exec command is docker context

for me it was not a server or daemon problem, but a context one

This answer helped me connecting to remote docker client and docker in docker via contexts :

• https://forums.docker.com/t/how-do-you-create-a-context-for-a-remote-tls-daemon/117275/3?u=abdelazizsharaf
• https://forums.docker.com/t/tls-over-context/128795?u=abdelazizsharaf this was my original quistion that this answer completed

So now we have both exposing docker via tcp and connecting to docker via tcp in this thread..

Another thing to think about is security

Is the exposed port with your methods are encrypted or not ?

docker:dind has two ports to expose

• 2375 no encrypton - context do not require cert or key
• 2376 encrypted - context require key pair to qualify connection

Is that encryption applicable with your methods ?

I think this is the part where we go inside docker:dind entry point file

so it should be this part

dockerd \
     --host="$dockerSocket" \
     --host=tcp://0.0.0.0:2376 \
     --tlsverify \
     --tlscacert "$DOCKER_TLS_CERTDIR/server/ca.pem" \
     --tlscert "$DOCKER_TLS_CERTDIR/server/cert.pem" \
     --tlskey "$DOCKER_TLS_CERTDIR/server/key.pem"

and @russellhoff : you are right

• the daemon server is running but as an entrypoint and not a service (I miss understood)

When i try to build the image be means of the BuildImage command, i am getting the

Connect to http://127.0.0.1:2375 [/127.0.0.1] failed: Connection refused: no further information

Apparently Gradle does not make match with the WSL platform IP.

thanks a lot

Great job
Thanks

@abel-delafuente tcp not http
you could also try to use a unix socket instead and test again to make sure if it's a docker behavior or a network restriction

Great! It's working for me.

Anyone having issues on DietPi? I am just getting familiar with DietPi and cannot get this to work.

that helped thank you!

Add /etc/systemd/system/docker.service.d/override.conf
[Service]
ExecStart=
ExecStart=/usr/bin/dockerd

I'm on a Synology NAS and I don't have the folder /etc/systemd/system/docker.service.d/override.conf ??? Any help on how to do step 2?

For everyone finding this page and looking for instructions for Synology's new Container Manager,

1. sudo vi /var/packages/ContainerManager/etc/dockerd.json

change to:
{"data-root":"/var/packages/ContainerManager/var/docker","log-driver":"db","registry-mirrors":[],"storage-driver":"aufs","hosts": ["tcp://0.0.0.0:2375", "unix:///var/run/docker.sock"]}

(basically add the stuff from the original step 1 to the end, without the curly-brackets {} )

2. systemctl daemon-reload

3. sudo systemctl restart pkg-ContainerManager-dockerd

You may need to repeat these steps when the Container Manager package gets updated. So far it's working for me

For everyone finding this page and looking for instructions for Synology's new Container Manager,

1. sudo vi /var/packages/ContainerManager/etc/dockerd.json

change to: {"data-root":"/var/packages/ContainerManager/var/docker","log-driver":"db","registry-mirrors":[],"storage-driver":"aufs","hosts": ["tcp://0.0.0.0:2375", "unix:///var/run/docker.sock"]}

(basically add the stuff from the original step 1 to the end, without the curly-brackets {} )

2. systemctl daemon-reload
3. sudo systemctl restart pkg-ContainerManager-dockerd

You may need to repeat these steps when the Container Manager package gets updated. So far it's working for me

Hi,bro. I'm trying to add the proxy option for the dockerd.json,there is some problem for me.
I had read the docs of how to set the value of daemon-proxy,but the error still exsit.

  "proxies": {
    "http-proxy": "http://proxy.example.com:80",
    "https-proxy": "https://proxy.example.com:443",
    "no-proxy": "*.test.example.com,.example.org",
  }

unable to configure the Docker daemon with file /var/packages/ContainerManager/etc/dockerd.json: the following directives don't match any configuration option: http-proxy, https-proxy, no-proxy

{"data-root":"/var/packages/ContainerManager/var/docker","log-driver":"db","proxies":{"http-proxy":"http://127.0.0.1:7890","https-proxy":"http://127.0.0.1:7890","no-proxy":"localhost,127.0.0.1"},"registry-mirrors":[],"storage-driver":"aufs"}
can you give me some help? appreciate it.

Sorry @honue , I don't know as I don't use proxies. Maybe Synology doesn't support those options. They are also using a slightly older version of docker. v20.10.23, build 876964a

ExecStart=
ExecStart=/usr/bin/dockerd --config-file /etc/docker/daemon.json

Thank you. This override.conf trick worked nicely for me. I used daemon.json to supply my TLS configuration as well as listen on 2376. Giving it nothing except a reference to daemon.json feels like a hack to avoid the hosts conflict.. but it works. Thanks again @webzakimbo

root@mnretrogamer029:~# cat /etc/docker/daemon.json
{
"data-root": "/mnt/dietpi_userdata/docker-data",
"log-driver": "journald",
"log-level": "warn",
"debug": false,
"hosts": ["unix:///var/run/docker.sock", "tcp://0.0.0.0:2376"],
"tlscacert": "/etc/docker/certs.d/ca.pem",
"tlscert": "/etc/docker/certs.d/server-cert.pem",
"tlskey": "/etc/docker/certs.d/server-key.pem",
"tlsverify": true
}

what if I don't have systemd? ie. Unraid/Slackware

on Ubuntu 22.04.3 couldn't get it to work with these instructions... do this:

Update Docker Configuration:
Edit the Docker daemon configuration file. The configuration file is typically located at /etc/docker/daemon.json. If it doesn't exist, you can create it.

sudo nano /etc/docker/daemon.json

Add the following content to the file:

{
"hosts": ["unix:///var/run/docker.sock", "tcp://0.0.0.0:2375"]
}

This configuration tells Docker to listen on both the UNIX socket and a TCP socket on all available network interfaces (0.0.0.0) on port 2375.

Restart Docker:
After making changes to the Docker daemon configuration, you need to restart the Docker daemon for the changes to take effect.

sudo systemctl restart docker

Adjust Firewall Rules (if necessary):
If you have a firewall enabled on your Ubuntu server, make sure to allow traffic on the Docker daemon port (default is 2375). You can use ufw (Uncomplicated Firewall) to do this:

bash

sudo ufw allow 2375

For Synology NAS (I am using DS923+) I found an easier way.
In your compose file for Homepage make sure to have the following listed under 'volumes'
- /var/run/docker.sock:/var/run/docker.sock

Then in your Homepage docker.yaml file, uncomment only this part:

# my-docker:
#   socket: /var/run/docker.sock

Once I did this it's working. Didn't have to mess with anything else.

Thanks for your gist! It works great for me, with special case where I use Windows 10 & WSL2!

thanks, it worked for me