Cargo is a system that we have developed at IBM Research to migrate containers along with their data with minimal downtime. Cargo leverages data federation capabilities of union filesystem to create a unified view of data (mainly the root file system) across the source and target hosts. This allows Cargo to start up a container almost immediately (within milliseconds) on the target host as the data from source root file system gets copied to target hosts either on-demand (using a copy-on-write (COW) partition) or lazily in the background (using rsync).

Cargo system primarily consist of following two components:

1. server: a centralized authority to orchestrate and manage the migration process.
2. agent: it needs to be installed on every docker host in the cluster. Agent is responsible for locally managing the container on the host.

NOTE: Before deploying this service into production, please perform adequate testing.

NOTE: Currently cargo supports migration of data volumes only. Support for 'rootfs' migration is under active development and will be added soon.

1. Flask framework

$ pip install Flask flask-restful

2. etcd Server

Cargo server uses etcd for storing the migration metadata. You can either download and install etcd on the server or you can simply instantiate a new etcd container.

$ docker  pull gcr.io/google_containers/etcd:2.0.12
$ docker run --net=host -d gcr.io/google_containers/etcd:2.0.12 /usr/local/bin/etcd --addr=127.0.0.1:4001
--bind-addr=0.0.0.0:4001 --data-dir=/var/etcd/data

3. etcd python client

$ git clone https://github.com/jplana/python-etcd.git
$ cd python-etcd/
$ python setup.py install

Download the source code (.zip) or clone from the git-repo.

$ cd cargo/server
$ python apiserver.py -h
Usage: python apiserver.py -c <config file>

Options:
  -h, --help            show this help message and exit
  -c CONFIG, --config=CONFIG
                        Config File(default=./config.cfg)

Update the config.cfg file as required.

For example:

$ python apiserver.py

Currently, it will not go deamon. It will print logs to the terminal

Follow this instructions to install agent on every docker host

1. Flask framework

$ pip install Flask flask-restful

2. docker-py

$ pip install docker-py

3. py-inotify Download the latest py-inotify package from https://pypi.python.org/pypi/python-inotify and add this to the python package list

$ wget https://pypi.python.org/packages/2.7/p/python-inotify/python-inotify-0.6-test.linux-x86_64.tar.gz#md5=28415492ec2de0312d84debdb0e9a037
$ tar -xvf python-inotify-0.6-test.linux-x86_64.tar.gz
$ cp -r ./usr/local/lib/python2.7/dist-packages/inotify /usr/local/lib/python2.7/dist-packages/
$ cp ./usr/local/lib/python2.7/dist-packages/python_inotify-0.6_test.egg-info /usr/local/lib/python2.7/dist-packages/ 

NOTE: This packages is expected to be bundled as .deb, to avoid manual install.

4. Setup password-less SSH between all agents

5. Setup NFS server and client on every docker host.

For example, on ubuntu hosts follow these instructions

$ apt-get install nfs-kernel-server #install server
$ apt-get install nfs-common # install client

And make sure the firewall rules are enabled for NFS mounting between docker hosts.

$ cd cargo/agent
$ python agent.py -h
Usage: python server.py -c <config file> 

Options:
  -h, --help            show this help message and exit
  -c CONFIG, --config=CONFIG

Update config.cfg file with docker deamon endpoint and cargo server details. For example

$ python agent.py

Currently, it will not go deamon. It will print logs to the terminal