Mar 31 2014

Docker, containers and simplicity.

Tag: devops,Docker,enterprise,new,redhat,RPM,virtualisation,windowsSven Dowideit @ 10:25 pm

I’ve now been working for Docker Inc. for 2 months. My primary role is Enterprise Support Engineer: I’m one of the guys that your company can turn to when the going gets tough, for training, or just generally to ask questions.

In these months, I’ve been working on Boot2Docker (OSX, Windows installers), our Documentation, and generally helping users come to terms with the broad spectrum of effects that Docker has on developing, managing and thinking about software components.

I’m still trying to work out ways to explain what Docker does – this is March’s version:

Virtual machines emulate complete computers, so you setup, maintain and run a complete Operating System, and copy around complete monolithic filesystem images.
Docker Containers emulate Operating Systems, allowing you to build, manage and run applications and services. And you copy around your application, data and configurations.

This might not quite feel right, given that images are build ‘FROM’ a base image – but one thought I have, is that as that base image (and most often some local modifications) are likely to be common to your entire infrastructure, that layer will be shared for all your containers. Chances are, you didn’t build it either – Tianon did :).

Solomon keeps reminding me that Dockerfiles are like Makefiles – and in the back of my mind, I think of our application image layers as packages, thin wrappers around applications that are then orchestrated together to produce your service. The base image you choose is only there to support that, and over time I’m sure we’ll simplify those much more.

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Dec 16 2013

Boot2Docker dom0 and more docker orchestration magic.

Tag: debian,devops,Docker,enterprise,open source,virtualisation,windowsSven Dowideit @ 11:53 pm

So, some concrete examples for my previous Boot2Docker rules post:dom0boot2docker

I’m modifying boot2docker to

  1. if present, auto-start an image named ‘dom0:latest’. This image then orchestrates the remainder of the system.
  2. my personal dom0 image starts sshd and the containers I want this system to auto-run.
  3. Set up a `home-volume` container, which I -volumes-from mount into all my development containers.

When I do some development, testing or production, it happens in containers, the base OS is pristine, and can be trivially updated (atm, i’m using boot from USB flash and SD Card).

Similarly, the dom0 container is also a bare busybox container, cloned from the filesystem of the boot2docker image itself.. I’m not ready for my end goal of doing this to my notebook and desktop – but then, this setup is only a few days old :).

This setup uses my detect existing /var/lib/docker on HD pull request , and the dom0-rootfs, dom0-base and dom0 images, and then from there, and initial dev image.

2 customisations I’ve made to the boot2docker are persisted on the HD – /var/lib/boot2docker/etc/hostname is set to something useful to me, and the optional /var/lib/boot2docker/ script starts the dom0 container at boot.

When I need a set of containers started, I can create a tiny orchestration container that can talk to the docker daemon and thus start more containers, controlling how they interact with each other and the outside world.


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Dec 09 2013

Boot2Docker for orchestration.

Tag: devops,Docker,enterprise,open source,virtualisationSven Dowideit @ 12:35 pm

Imagine that you have a PXE / USB / boot setup that boots in seconds, and as its last step, starts a docker privileged image labeled ‘dom0:latest’.

Most importantly, each of these servers then would ‘docker pull’ and ‘docker run’ the services and applications it provides – without modifying the base OS, or ‘dom0′

It also gives the server farm admin the opportunity to make a customized ‘dom0:latest’ image – containing the farm’s ‘dom0:latest’ thus orchestrating the inner container configurations further.


I’m using boot2docker on my ‘docker-server’ (an old x61 thinkpad), and using the inbuilt harddrive to store the docker images that are run on it. I’m totally avoiding modifying the base OS, and doing all the work in containers – enabling very fast run and teardown for development and testing.

now if only ‘turnbull-net’ wasn’t totally useless for pulling images (gee, thanks Malcolm Turnbull, 1MB ADSL with constant dropouts in the middle of Brisbane is sooooooo conducive to working).


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Dec 05 2013

Docker container network portability

Tag: devops,Docker,open source,virtualisationSven Dowideit @ 4:18 pm

Rather than hardcoding network links between a service consumer and provider, Docker encourages service portability.

eg, instead of 2 containers talking directly to each other:

(consumer) --> (redis)

requiring you to restart the consumer to attach it to a different redis service, you can add ambassador containers:

(consumer) --> (redis-ambassador) --> (redis)


(consumer) --> (redis-ambassador) ---network---> (redis-ambassador) --> (redis)

When you need to rewire your consumer to talk to a different resdis server, you can just restart the redis-ambassador container that the consumer is connected to.

This pattern also allows you to transparently move the redis server to a different docker host from the consumer.

Using the svendowideit/ambassador container, the link wiring is controlled entirely from the dockerrun parameters.

Two host Example

Start actual redis server on one Docker host

big-server $ docker run -d -name redis crosbymichael/redis

Then add an ambassador linked to the redis server, mapping a port to the outside world

big-server $ docker run -d -link redis:redis -name redis_ambassador -p 6379:6379 svendowideit/ambassador

On the other host, you can set up another ambassador setting environment variables for each remote port we want to proxy to the big-server

client-server $ docker run -d -name redis_ambassador -expose 6379 -e REDIS_PORT_6379_TCP=tcp:// svendowideit/ambassador

Then on the client-server host, you can use a redis client container to talk to the remote redis server, just by linking to the local redis ambassador.

client-server $ docker run -i -t -rm -link redis_ambassador:redis relateiq/redis-cli
redis> ping

How it works

The following example shows what the svendowideit/ambassador container does automatically (with a tiny amount of sed)

On the docker host ( that redis will run on:

# start actual redis server
$ docker run -d -name redis crosbymichael/redis

# get a redis-cli container for connection testing
$ docker pull relateiq/redis-cli

# test the redis server by talking to it directly
$ docker run -t -i -rm -link redis:redis relateiq/redis-cli
redis> ping

# add redis ambassador
$ docker run -t -i -link redis:redis -name redis_ambassador -p 6379:6379 busybox sh

in the redis_ambassador container, you can see the linked redis containers’s env

$ env

This environment is used by the ambassador socat script to expose redis to the world (via the -p 6379:6379 port mapping)

$ docker rm redis_ambassador
$ sudo ./contrib/
$ docker run -t -i -link redis:redis -name redis_ambassador -p 6379:6379 docker-ut sh

$ socat TCP4-LISTEN:6379,fork,reuseaddr TCP4:

then ping the redis server via the ambassador

Now goto a different server

$ sudo ./contrib/
$ docker run -t -i  -expose 6379 -name redis_ambassador docker-ut sh

$ socat TCP4-LISTEN:6379,fork,reuseaddr TCP4:

and get the redis-cli image so we can talk over the ambassador bridge

$ docker pull relateiq/redis-cli
$ docker run -i -t -rm -link redis_ambassador:redis relateiq/redis-cli
redis> ping

The svendowideit/ambassador Dockerfile

The svendowideit/ambassador image is a small busybox image with socat built in. When you start the container, it uses a small sed script to parse out the (possibly multiple) link environment variables to set up the port forwarding. On the remote host, you need to set the variable using the -e command line option.

-expose 1234 -e REDIS_PORT_1234_TCP=tcp:// will forward the local 1234port to the remote IP and port – in this case

# first you need to build the docker-ut image using ./contrib/
# then
#   docker build -t SvenDowideit/ambassador .
#   docker tag SvenDowideit/ambassador ambassador
# then to run it (on the host that has the real backend on it)
#   docker run -t -i -link redis:redis -name redis_ambassador -p 6379:6379 ambassador
# on the remote host, you can set up another ambassador
#    docker run -t -i -name redis_ambassador -expose 6379 sh

FROM    docker-ut

CMD     env | grep _TCP= | sed 's/.*_PORT_\([0-9]*\)_TCP=tcp:\/\/\(.*\):\(.*\)/socat TCP4-LISTEN:\1,fork,reuseaddr TCP4:\2:\3 \&/'  | sh && top

(this is pull request so will eventually find its way into the Docker documentation)
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Nov 27 2013

Docker 0.7 is here – welcome RPM distros (and anyone else that lacks AUFS)

The Docker project has continued its mostly-monthly releases with the long anticipated 0.7 release, this time making the storage backend pluggable, so fedora/redhat based users can use it without building a custom kernel.

I’m curious to see the performance differences between the 3 storage backends we have now – but I need to assimilate the wonders of Linking containers for adhoc scaling first.

Try it out – I’m even more convinced that Docker containers have an interesting future :)

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Oct 15 2013

easy install of on Debian

Tag: debian,devops,Docker,new,virtualisationSven Dowideit @ 9:05 pm

UPDATE: for Docker 0.6.5, the ubuntu debian package also installs on Debian. You still need to enable IPv4 forwarding as below – then re-start the docker daemon

I’ve been doing some work on Docker – learning golang, Docker internals, and just some of the command line options that I didn’t know I needed to know about.

Because I was in a hurry, I threw an old unused disk into one of my old laptops and installed ubuntu. That was enough for me to learn that I wanted to know alot more about Docker.

So, I’m back to using the loaner T530 with my 128GB SSD in it – its been running Debian since the day I got the SSD, over 2 years ago.

it turns out that on Debian testing (with the 3.10-3-amd64 kernel), its incredibly easy to run docker:

sudo apt-get install lxc wget bsdtar curl golang git aufs-tools mercurial iptables
wget --output-document=docker
chmod +x docker
sudo su -
#enable IPv4 forwarding
echo "net.ipv4.ip_forward = 1" >> /etc/sysctl.conf
sysctl -p /etc/sysctl.conf
# set up and mount the cgroup mountpoint
echo 'none /sys/fs/cgroup cgroup defaults 0 0' | sudo tee -a /etc/fstab
mount /sys/fs/cgroup
#OK, you might need to reboot if it fails to mount?
./docker -d &

from there, you can run the docker cli like normal (except that its not in your path yet).

I’m going to pull over the apt pinning installation documentation I wrote for publican the other week and re-write it (and test) for installing docker on Debian Stable, and we’ll all be much happier.

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