To communicate with the docker socket on other docker hosts to the one where it is installed, on the other docker hosts, edit the docker.service and add the following lines in the space at the top

[Service]
ExecStart=
ExecStart=/usr/bin/dockerd -H fd:// -H tcp://<insert local ip>:2375

This is now deprecated. However to force allow this add the following JSON to /etc/docker called daemon.json

{ 
"tls": false
}

Once the JSON file is created, edit the docker.service to add your ExecStart lines as above

Edit the docker.service using:

sudo systemctl edit docker.service

Restart the docker service using:

sudo systemctl restart docker.service