Connecting to a Remote Docker Daemon - docker

Question

I have installed VirtualBox and installed Ubuntu server version in VirtualBox VM. My host machine is Windows 10.
I have also installed Docker in my host Windows box. My intention is to use the docker CLI in Windows to connect to docker daemon (server) inside the VM.
I have made the changes in the Ubuntu VM and it is listening at port 2375.
tcp 0 0 127.0.0.1:2375 0.0.0.0:* LISTEN 2305/dockerd
Also I have set the environment variable DOCKER_HOST in my host(Windows) to the VM machine IP and port.
set DOCKER_HOST=tcp://192.168.56.107:2375
My Windows machine IP is 192.168.56.1 and the ping is working fine.
Pinging 192.168.56.107 with 32 bytes of data:
Reply from 192.168.56.107: bytes=32 time<1ms TTL=64
Reply from 192.168.56.107: bytes=32 time<1ms TTL=64
But when I try to connect from my Windows machine, it gives the following error:
error during connect: Get http://192.168.56.107:2375/v1.27/info: dial tcp 192.168.56.107:2375: connectex: No connection could be made because the target machine actively refused it.
Please find docker info output:
controller#ubuntuserver:~$ docker info
Containers: 4
Running: 0
Paused: 0
Stopped: 4
Images: 2
Server Version: 18.09.6
Storage Driver: overlay2
Backing Filesystem: extfs
Supports d_type: true
Native Overlay Diff: true
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
Volume: local
Network: bridge host macvlan null overlay
Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
Swarm: inactive
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: bb71b10fd8f58240ca47fbb579b9d1028eea7c84
runc version: 2b18fe1d885ee5083ef9f0838fee39b62d653e30
init version: fec3683
Security Options:
apparmor
seccomp
Profile: default
Kernel Version: 4.15.0-50-generic
Operating System: Ubuntu 18.04.2 LTS
OSType: linux
Architecture: x86_64
CPUs: 2
Total Memory: 7.79GiB
Name: ubuntuserver
ID: AWDW:34ET:4J2J:2NWB:UPK7:EQHB:W64E:22AT:W6J4:BMRD:NDO6:CNR2
Docker Root Dir: /var/lib/docker
Debug Mode (client): false
Debug Mode (server): false
Registry: https://index.docker.io/v1/
Labels:
Experimental: false
Insecure Registries:
127.0.0.0/8
Live Restore Enabled: false
Product License: Community Engine
WARNING: API is accessible on http://127.0.0.1:2375 without encryption.
Access to the remote API is equivalent to root access on the host. Refer
to the 'Docker daemon attack surface' section in the documentation for
more information: https://docs.docker.com/engine/security/security/#docker-daemon-attack-surface
WARNING: No swap limit support
cat /lib/systemd/system/docker.service
[Unit]
Description=Docker Application Container Engine
Documentation=https://docs.docker.com
BindsTo=containerd.service
After=network-online.target firewalld.service containerd.service
Wants=network-online.target
Requires=docker.socket
[Service]
Type=notify
# the default is not to use systemd for cgroups because the delegate issues still
# exists and systemd currently does not support the cgroup feature set required
# for containers run by docker
ExecStart=/usr/bin/dockerd -H fd:// -H tcp://0.0.0.0:2375 --containerd=/run/containerd/containerd.sock
ExecReload=/bin/kill -s HUP $MAINPID
TimeoutSec=0
RestartSec=2
Restart=always
# Note that StartLimit* options were moved from "Service" to "Unit" in systemd 229.
# Both the old, and new location are accepted by systemd 229 and up, so using the old location
# to make them work for either version of systemd.
StartLimitBurst=3
# Note that StartLimitInterval was renamed to StartLimitIntervalSec in systemd 230.
# Both the old, and new name are accepted by systemd 230 and up, so using the old name to make
# this option work for either version of systemd.
StartLimitInterval=60s
# Having non-zero Limit*s causes performance problems due to accounting overhead
# in the kernel. We recommend using cgroups to do container-local accounting.
LimitNOFILE=infinity
LimitNPROC=infinity
LimitCORE=infinity
# Comment TasksMax if your systemd version does not supports it.
# Only systemd 226 and above support this option.
TasksMax=infinity
# set delegate yes so that systemd does not reset the cgroups of docker containers
Delegate=yes
# kill only the docker process, not all processes in the cgroup
KillMode=process
[Install]
WantedBy=multi-user.target
Can you please help me to resolve this?

Answer 1

You need to configure the Docker daemon in your ubuntu server in order for it to accept tcp connection.
By default Docker listen on the unix socket /var/run/docker.sock.
To configure your daemon, you can have a look at the documentation here
Step-by-step configuration (in this example, everything is done on the Ubuntu VM) :
Configure the daemon
On Ubuntu, by default you are using systemd. You need to edit the configuration file (usually located in /lib/systemd/system/docker.service) :
[Service]
ExecStart=/usr/bin/dockerd --containerd=/run/containerd/containerd.sock -H tcp://0.0.0.0:2375
With this example, the Docker daemon no longer listen on the unix socket. It only listen on tcp call from localhost.
Restart the daemon :
$> sudo systemctl daemon-reload
$> sudo systemctl restart docker.service
Configure the client (still on the VM)
After restarting the daemon, your docker client does not work anymore (as you've just told the client to only listen to tcp connection). Thus, if you do docker image ls it should not respond. In order for your client to work, you need to tell it which server to connect to :
$> export DOCKER_HOST="tcp://0.0.0.0:2375"
Now, your client should be able to connect to the daemon (i.e : docker image ls should print all the images)
This should work fine on your Ubuntu server. You just need to apply the same client configuration on Windows. If it does not work on Windows, then it means something else is blocking the trafic (probably a firewall).
Hope this helps.

Answer 2

Maybe your server ICMP protocol has been prohibited,check it by this cmd:
iptables -L INPUT --line-numbers
and if terminal shows:
and delete this record by cmd
iptables -D INPUT 7
Hope this helps.