random neuron misfires

Playing more and more with Docker across multiple Linux distributions has taught me that not all Linux distributions are treated the same.

There’s a discord right now in the Linux community about systemd vs. SysV init. In our example, CentOS 7.x uses systemd, where all system services are spawned and started.

I am using this version of Linux to set up my own Docker lab host for tire-kicking, but it needs some tweaks.

I also wanted to see if I could use the Docker API from my Android phone, using DockerDroid, which (after configuring this) works famously!

Here’s what you need to do:

1. Log into your CentOS machine and update to the most-current Docker version. The version shipped with CentOS 7 in the repo as I write this post, is “docker-1.3.2-4.el7.centos.x86_64”. You want to be using something more current, and 1.4 is the latest. To fetch that (and preserve your existing version), run the following:

   $ su -
   # cd /bin && mv /bin/docker /bin/docker.el7
   # wget https://get.docker.com/builds/Linux/x86_64/docker-latest -O docker
   # systemctl restart docker
   # exit
   $ 
   

   Now you should have a working Docker with the right version (current). You can verify that:

   $ sudo docker version
   Client version: 1.4.1
   Client API version: 1.16
   Go version (client): go1.3.3
   Git commit (client): 5bc2ff8
   OS/Arch (client): linux/amd64
   Server version: 1.4.1
   Server API version: 1.16
   Go version (server): go1.3.3
   Git commit (server): 5bc2ff8

2. So far, so good! Now we need to make sure firewalld has a rule to permit this port to be exposed for external connections:

   $ sudo firewall-cmd --zone=public --add-port=4243/tcp --permanent
   $ sudo firewall-cmd --reload
   success
   

   You can verify that this new rule was added, by looking at /etc/firewalld/zones/public.xml, which should now have a line that looks like this:

   <port protocol="tcp" port="4243"/>

3. Now let’s reconfigure Docker to expose the API to external client connections, by making sure the OPTIONS line in /etc/sysconfig/docker looks like this (note the portion in bold):

   OPTIONS=--selinux-enabled -H fd:// -H tcp://0.0.0.0:4243
   

4. Restart the Docker service to enact the API on that port (if successful, you will not see any output):

   sudo systemctl restart docker

5. To test the port locally, install telnet and then try telnet’ing to the port on localhost:

   $ sudo telnet localhost 4243
   Trying ::1...
   Connected to localhost.
   Escape character is '^]'.
   
   HTTP/1.1 400 Bad Request
   
   Connection closed by foreign host.

   All looks good so far!

6. Lastly, install DockerDroid and configure it to talk to your server on this port:

   

Now you should be able to use DockerDroid to navigate your Images, Containers and API.

Good luck!