crane

Crane

Lift containers with ease

Overview

Crane is a little tool to orchestrate Docker containers. It works by reading in some configuration (JSON or YAML) which describes how to obtain images and how to run the containers. This simplifies setting up a development environemt a lot as you don't have to bring up every container manually, remembering all the arguments you need to pass. By storing the configuration next to the data and the app(s) in a repository, you can easily share the whole environment.

Installation

The latest release can be installed via:

bash -c "`curl -sL https://raw.githubusercontent.com/michaelsauter/crane/master/download.sh`" && sudo mv crane /usr/local/bin/crane

You can also build Crane yourself by using the Go toolchain (go get and go install). Please have a look at the release notes for the changelog if you're upgrading.

Of course, you will need to have Docker (>= 1.0) installed on your system. I generally recommend to do this on Ubuntu, but if you are on OS X, you can also try docker-osx. boot2docker is nice, but unfortunately, it does not support bind-mounting volumes yet.

Usage

Crane is a very light wrapper around the Docker commands. This means that most commands just call the corresponding Docker commands, but for all targeted containers. Additionally, there are a few special commands.

run

Maps to docker run. If a container already exists, it is just started. However, containers can be recreated by passing --recreate.

rm

Maps to docker rm. Running containers can be killed first with --kill.

kill

Maps to docker kill.

start

Maps to docker start.

stop

Maps to docker stop.

provision

Either calls Docker's build or pull, depending on whether a Dockerfile is specified. The Docker cache can be disabled by passing --no-cache.

lift

Will provision and run the containers in one go. By default, it does as little as possible to get the containers running. This means it only provisions images if necessary and just starts containers if they already exist. To update the images and recreate the containers, pass --recreate (and optionally --no-cache).

status

Displays information about the state of the containers.

You can get more information about what's happening behind the scenes for all commands by using --verbose. All options have a short version as well, e.g. lift -rn.

crane.json / crane.yaml

The configuration defines an array of containers in either JSON or YAML. By default, the configuration is expected in the current directory (crane.json or crane.yaml/crane.yml), but it can also be specified via --config. If a container depends on another one, it must appear before that container in the configuration file. Every container consists of:

• name (string, required): Name of the container
• image (string, required): Name of the image to build/pull
• dockerfile (string, optional): Relative path to the Dockerfile
• run (object, optional): Parameters mapped to Docker's run.
  • cidfile (string)
  • cpu-shares (integer)
  • detach (boolean) sudo docker attach <container name> will work as normal.
  • dns (array)
  • env (array)
  • env-file (string)
  • expose (array) Ports to expose to linked containers.
  • hostname (string)
  • interactive (boolean)
  • link (array) Link containers.
  • lxc-conf (array)
  • memory (string)
  • privileged (boolean)
  • publish (array) Map network ports to the container.
  • publish-all (boolean)
  • rm (boolean)
  • tty (boolean)
  • user (string)
  • volume (array) In contrast to plain Docker, the host path can be relative.
  • volumes-from (array) Mount volumes from other containers
  • workdir (string)
  • cmd (array/string) Command to append to docker run (overwriting CMD).

See the Docker documentation for more details about the parameters.

Example

For demonstration purposes, we'll bring up a PHP app (served by Apache) that depends both on a MySQL database and a Memcached server. The source code is available at http://github.com/michaelsauter/crane-example. Here's what the crane.json looks like:

{
	"containers": [
		{
			"name": "apache",
			"dockerfile": "apache",
			"image": "michaelsauter/apache",
			"run": {
				"volumes-from": ["crane_app"],
				"publish": ["80:80"],
				"link": ["crane_mysql:db", "crane_memcached:cache"],
				"detach": true
			}
		},
		{
			"name": "app",
			"dockerfile": "app",
			"image": "michaelsauter/app",
			"run": {
				"volume": ["app/www:/srv/www:rw"],
				"detach": true
			}
		},
		{
			"name": "mysql",
			"dockerfile": "mysql",
			"image": "michaelsauter/mysql",
			"run": {
				"detach": true
			}
		},
		{
			"name": "memcached",
			"dockerfile": "memcached",
			"image": "michaelsauter/memcached",
			"run": {
				"detach": true
			}
		}
	]
}

If you have Docker installed, you can just clone that repository and bring up the environment right now. In the folder where the crane.json is, type:

[sudo] crane lift

This will bring up the containers. The container running Apache has the MySQL and Memcached containers automatically linked. Open http://localhost and you should be greeted with "Hello World".

If you want to use YAML instead of JSON, here's what a simple configuration looks like:

containers:
	- name: pry
		image: d11wtq/ruby
		run:
			interactive: true
			tty: true
			cmd: pry

Advanced Usage

Next to containers, you can also specify groups, and then execute Crane commands that only target those groups. If you do not specify --target, the command will apply to all containers. However, you can override the default by specifying a default group. Also, every container can be targeted by using the name of the container as an argument to --target. Groups of containers can be specifiec like this (YAML shown):

groups:
	databases: ["database1", "database2"]
	development: ["container1", "container2"]

This could be used like so: crane provision --target="container1" or crane run --target="databases".

Other Crane-backed environments

• Silex + Nginx/php-fpm + MySQL
• Symfony2 + Apache + MySQL
• Sinatra + PostrgeSQL