connect to docker daemon from inside docker container - docker

Question

Im trying configure the docker daemon so i can connect to it from inside the docker containers i start..
So i changed /etc/docker/daemon.json to
{
"hosts": ["unix:///var/run/docker.sock", "tcp://0.0.0.0:2375"]
}
So that i connect to it through the docker bridge.. However when i restart docker i get
netstat -tunlp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address
State PID/Program name
tcp 0 0 127.0.0.1:3306 0.0.0.0:* LISTEN 3728/mysqld
tcp 0 0 127.0.0.1:6379 0.0.0.0:* LISTEN 24253/redis-server
tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN 3756/nginx
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 3634/sshd
tcp 0 0 0.0.0.0:443 0.0.0.0:* LISTEN 3756/nginx
tcp6 0 0 :::8010 :::* LISTEN 4230/apache2
tcp6 0 0 :::9200 :::* LISTEN 26824/java
tcp6 0 0 :::9300 :::* LISTEN 26824/java
tcp6 0 0 :::22 :::* LISTEN 3634/sshd
tcp6 0 0 :::2375 :::* LISTEN 1955/dockerd
So first i though the issue was the fact that it was listening on ipv6 not ipv4. and according to
Make docker use IPv4 for port binding
It should all still work but it doesnt.. When i try
telnet 172.17.0.1(docker host) 2375
it fails to connect while
telnet 172.17.0.1(docker host) 80
works. How can i connect to docker running on the host machine? Im running on Ubuntu 14.04.5 docker Version: 17.06.2-ce

Answer 1

You can start your containers mounting the host docker socket into your containers.
docker run -v /var/run/docker.sock:/var/run/docker.sock ...
With this setup, Docker clients inside the containers will be using the Docker daemon from the host. Your containers will be able to build, run, push etc. using daemon running in host. Please note that with these setup everything is happening on the host, so if you start new containers they will be “sibling” containers.
EDIT
If you are using the bridge network, you can connect to any service running on host machine using host IP address.
For example, I have mysqld running on my host with IP 10.0.0.1 and from a container I can do
mysql -u user -p -h 10.0.0.1
The trick is to find out the host IP address from containers.
In Docker for Mac (I am running version 17.07.0) is as simple as connecting to the special host "docker.for.mac.localhost"
Another option is to add an alias IP to your loopback interface
sudo ifconfig lo0 alias 192.168.1.1
And then when running containers add a host for this alias IP
docker run --rm -ti --add-host host-machine:192.168.1.1 mysql:5.7 bash
With this setup, inside container you should be able to do
mysql -u user -p -h host-machine

Answer 2

This answer may be a bit late, but it's better late than never as we never can tell who may be experiencing similar problem. I just fixed it be disabling the unnecessary ufw rule blocking the internal communication.
Example:
sudo ufw allow from <IP address or range> to any port [desired port]
sudo ufw allow from 172.16.0.0/12 to any port 3421.
As for me, I disabled the UFW service totally using the command below.
sudo ufw disable