Boot2Docker

Boot2Docker is a lightweight Linux distribution made specifically to run Docker containers. It runs completely from RAM, is a ~45MB download and boots quickly.

Important Note

Boot2Docker is officially in maintenance mode -- it is recommended that users transition from Boot2Docker over to Docker for Mac or Docker for Windows instead.

What this means concretely is new Docker releases, kernel updates, etc, but concerted attempts to keep new features/functionality to an absolute minimum to ensure continued maintainability for the few folks who can't yet transition to the better-suited Docker for Windows / Docker for Mac products (Windows 7 users who can't Docker for Windows at all, Windows 10 Home users who thus can't Hyper-V, VirtualBox users who thus can't Hyper-V, etc etc).

See docker/machine#4537 for some useful discussion around Docker Machine also being in a similar state.

Features

• Recent Linux Kernel, Docker pre-installed and ready-to-use
• VM guest additions (VirtualBox)
• Container persistence via disk automount on /var/lib/docker
• SSH keys persistence via disk automount

Note: Boot2Docker uses port 2376, the registered IANA Docker TLS port

Caveat Emptor

Boot2Docker is designed and tuned for development. Using it for any kind of production workloads is highly discouraged.

Installation

Installation should be performed via Docker Toolbox which installs Docker Machine, the Boot2Docker VM, and other necessary tools.

The ISO can be downloaded here.

How to use

Boot2Docker is used via Docker Machine (installed as part of Docker Toolbox) which leverages VirtualBox's VBoxManage to initialise, start, stop and delete the VM right from the command line.

More information

See Frequently asked questions for more details.

Boot script log

The bootup script output is logged to /boot.log, so you can see (and potentially debug) what happens. Note that this is not persistent between boots because we're logging from before the persistence partition is mounted (and it may not exist at all).

Docker daemon options

If you need to customize the options used to start the Docker daemon, you can do so by adding entries to the /var/lib/boot2docker/profile file on the persistent partition inside the Boot2Docker virtual machine. Then restart the daemon.

The following example will enable core dumps inside containers, but you can specify any other options you may need.

docker-machine ssh default -t sudo vi /var/lib/boot2docker/profile
# Add something like:
#     EXTRA_ARGS="--default-ulimit core=-1"
docker-machine restart default

Installing secure Registry certificates

As discussed in the Docker Engine documentation certificates should be placed at /etc/docker/certs.d/hostname/ca.crt where hostname is your Registry server's hostname.

docker-machine scp certfile default:ca.crt
docker-machine ssh default
sudo mv ~/ca.crt /etc/docker/certs.d/hostname/ca.crt
exit
docker-machine restart

Alternatively the older Boot2Docker method can be used and you can add your Registry server's public certificate (in .pem or .crt format) into the /var/lib/boot2docker/certs/ directory, and Boot2Docker will automatically load it from the persistence partition at boot.

You may need to add several certificates (as separate .pem or .crt files) to this directory, depending on the CA signing chain used for your certificate.

Insecure Registry

As of Docker version 1.3.1, if your registry doesn't support HTTPS, you must add it as an insecure registry.

$ docker-machine ssh default "echo $'EXTRA_ARGS=\"--insecure-registry <YOUR INSECURE HOST>\"' | sudo tee -a /var/lib/boot2docker/profile && sudo /etc/init.d/docker restart"

then you should be able to do a docker push/pull.

Running behind a VPN (Cisco AnyConnect, etc)

So sometimes if you are behind a VPN, you'll get an i/o timeout error. The current work around is to forward the port in the boot2docker-vm.

If you get an error like the following:

Sending build context to Docker daemon
2014/11/19 13:53:33 Post https://192.168.59.103:2376/v1.15/build?rm=1&t=your-tag: dial tcp 192.168.59.103:2376: i/o timeout

That means you have to forward port 2376, which can be done like so:

• Open VirtualBox
• Open Settings > Network for your 'default' VM
• Select the adapter that is 'Attached To': 'NAT' and click 'Port Forwarding'.
• Add a new rule:
  • Protocol: TCP
  • Host IP: 127.0.0.1
  • Host Port: 5555
  • Guest Port: 2376
• Set DOCKER_HOST to 'tcp://127.0.0.1:5555'

SSH into VM

$ docker-machine ssh default

Docker Machine auto logs in using the generated SSH key, but if you want to SSH into the machine manually (or you're not using a Docker Machine managed VM), the credentials are:

user: docker
pass: tcuser

Persist data

Boot2docker uses Tiny Core Linux, which runs from RAM and so does not persist filesystem changes by default.

When you run docker-machine, the tool auto-creates a disk that will be automounted and used to persist your docker data in /var/lib/docker and /var/lib/boot2docker. This virtual disk will be removed when you run docker-machine delete default. It will also persist the SSH keys of the machine. Changes outside of these directories will be lost after powering down or restarting the VM.

If you are not using the Docker Machine management tool, you can create an ext4 formatted partition with the label boot2docker-data (mkfs.ext4 -L boot2docker-data /dev/sdX5) to your VM or host, and Boot2Docker will automount it on /mnt/sdX and then softlink /mnt/sdX/var/lib/docker to /var/lib/docker.