Cannot connect to the Docker daemon (port 2375)

Question

I have installed Docker on Ubuntu 16.04 server, using the manual on this page: https://docs.docker.com/cs-engine/1.13/, so, using these steps:

curl -fsSL 'https://sks-keyservers.net/pks/lookup?op=get&search=0xee6d536cf7dc86e2d7d56f59a178ac6c6238f52e' | sudo apt-key add -
sudo add-apt-repository    "deb https://packages.docker.com/1.13/apt/repo/ \
ubuntu-$(lsb_release -cs) \
main"

sudo apt-get update
sudo apt-get -y install docker-engine

I have installed it on two servers and I need them to see each other, I needed to let Docker daemon listen on port 2375 (probably doesn't matter, but using this manual: https://github.com/yeasy/cello/blob/master/docs/deployment.md)

So I created the conf file:

sudo mkdir -p /etc/systemd/system/docker.service.d
sudo vim /etc/systemd/system/docker.service.d/override.conf

Added this to the override.conf:

[Service]
DOCKER_OPTS="$DOCKER_OPTS -H tcp://0.0.0.0:2375 -H unix:///var/run/docker.sock --api-cors-header='*' --default-ulimit=nofile=8192:16384 --default-ulimit=nproc=8192:16384"
EnvironmentFile=-/etc/default/docker
ExecStart=
ExecStart=/usr/bin/dockerd -H fd:// $DOCKER_OPTS

Then:

$ sudo systemctl daemon-reload
$ sudo systemctl restart docker.service

Tested the connection between servers like this:

$ docker -H 10.101.35.61:2375 version

The response:

Client:
 Version:      1.13.1-cs4
 API version:  1.27
 Go version:   go1.7.5
 Git commit:   e46aec0
 Built:        Mon May 22 18:46:40 2017
 OS/Arch:      linux/amd64
Cannot connect to the Docker daemon at tcp://10.101.35.61:2375. Is the docker daemon running?

Tried restarting the server, same problem. Tried to run with sudo. Tried adding the user to group docker:

sudo usermod -aG docker $USER

Didn't help. I have disabled firewall on both servers. When I check the ports open on the server with sudo lsof -i, I can't see anything listening to port 2375 - I am guessing Docker should be listening to it?

Answer 1

Try the config file in this location, create it if it does not exist:

/etc/docker/daemon.json

Put this and restart the docker service:

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

You can add more configs, documented here.