How to make docker listening to unix and TCP socket under centos with systemd

So don't touch the docker.socket file or anything. Systemd has a concept of DropIns and you can override parts of the services using a dropin file.

So create the dropin folder for the service first

mkdir -p /etc/systemd/system/docker.service.d/

Then your create a config file

cat > /etc/systemd/system/docker.service.d/90-docker.conf <<EOF[Service]ExecStart=ExecStart=/usr/bin/docker daemon -H fd:// -H tcp://0.0.0.0:2375

The first ExecStart= blanks the original command and second ExecStart specifies the new command we want to override

Now we should restart the docker service

systemctl daemon-reloadsystemctl restart docker

Now your service would also be listening at 2375. I believe currently the host option cannot be controlled using /etc/docker/daemon.json. See the below link for more details

https://docs.docker.com/engine/reference/commandline/dockerd/#docker-runtime-execution-options

1. cd /lib/systemd/system/
2. vim docker-tcp.socket

3. paste thie to docker-tcp.socket

   [Unit]Description=Docker Socket for the APIPartOf=docker.service[Socket]ListenStream=2375BindIPv6Only=bothService=docker.service[Install]WantedBy=sockets.target

4. systemctl daemon-reload

5. systemctl stop docker.service
6. systemctl enable docker-tcp.socket
7. systemctl start docker-tcp.socket
8. systemctl start docker.service
9. verify 2375 port is opened docker -H 127.0.0.1 ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES

I actually just posted this answer to an open issue on Github for PhotonOS. I created a gist with the instructions doc markdown as well as the equivalent shell script.

It allows for maintaining both local unix socket as well as remote TCP-based access to the API. Unlike most instructions, it follows the Docker supported method of creating the docker.socket service and binding it to docker service as a dependency, rather than hard-coding either/or TCP or unix fd sock on the command line, or hacking any system files that get overwritten at every upgrade.

Gist is at: https://git.io/fjhhO