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Efficient and reproducible software deployment for EC2 instances

Project description


To install and use CGCloud, you need


Read the entire section before pasting any commands and ensure that all prerequisites are installed. It is recommended to install CGCloud into a virtualenv. Create a virtualenv and use pip to install the cgcloud-core package:

virtualenv ~/cgcloud
source ~/cgcloud/bin/activate
pip install cgcloud-core
  • If you get DistributionNotFound: No distributions matching the version for cgcloud-core, try running pip install --pre cgcloud-core.

  • If you get an error about yaml.h being missing you may need to install libyaml (via HomeBrew on OS X) or libyaml-dev (via apt-get or yum on Linux).

  • If you get

    AttributeError: 'tuple' object has no attribute 'is_prerelease'

    you may need to upgrade setuptools

    sudo pip install --upgrade setuptools
  • If you get

    ImportError: cannot import name cgcloud_version

    you may need to upgrade virtualenv

    sudo pip install --upgrade virtualenv
  • If, on Mountain Lion, you get:

    clang: error: unknown argument: '-mno-fused-madd' [-Wunused-command-line-argument-hard-error-in-future]
    clang: note: this will be a hard error (cannot be downgraded to a warning) in the future
    error: command 'clang' failed with exit status 1

    try the following work-around:

    export CFLAGS=-Qunused-arguments
    export CPPFLAGS=-Qunused-arguments

The installer places the cgcloud executable into the bin directory of the virtualenv. Before you can invoke cgcloud, you have to activate the virtualenv as shown above. Alternatively, create a per-user bin directory and symlink the cgcloud executable into it:

mkdir -p ~/bin
ln -snf ~/cgcloud/bin/cgcloud ~/bin

After adding export PATH="$HOME/bin:$PATH" to your to your ~/.profile, ~/.bash_profile or ~/.bashrc, you won’t need to explicitly activate the virtualenv before running cgcloud.

You should be able to invoke cgcloud now:

cgcloud --help

Auto-completion for Bash

Install the awesome argcomplete module:

pip install argcomplete

Then add the following command to your ~/.profile:

eval "$(/absolute/path/to/virtualenv/bin/register-python-argcomplete cgcloud)"


Access keys

Ask your AWS admin to setup an IAM account in AWS for you. Log into Amazon’s IAM console and generate an access key for yourself. While your IAM username and password are used to authenticate yourself for interactive use via the AWS console, the access key is used for programmatic access via cgcloud.

Once you have an access key, create ~/.boto on you local computer with the following contents:

aws_access_key_id = PASTE_YOUR_ACCESS_KEY_ID_HERE
aws_secret_access_key = PASTE_YOUR_SECRET_ACCESS_KEY_HERE

The ~/.boto file is being deprecated. Consider using ~/.aws/credentials instead. It is supported by various AWS SDKs and allows for easily switching between different AWS accounts (profiles):



To choose an active profile, set the AWS_PROFILE environment variable:

export AWS_PROFILE=foo

EC2 region and availability zone

Edit your ~/.profile or ~/.bash_profile and add the following line:

export CGCLOUD_ZONE=us-west-2a

This configures both the region us-west-2 and the availability zone within that region: a. Instead of us-west-2a you could use us-east-1a or any other zone in any other EC2 region.

Public SSH key

If you don’t have an SSH key, you can create one using the ssh-keygen command. Do not use the EC2 console to generate a key. This would be insecure and produce a key that is incompatible with CGCloud.

Register your SSH key in EC2 by running:

cgcloud register-key ~/.ssh/

The above command imports the given public key to EC2 as a key pair (I know, the terminology is confusing) but also uploads it to S3, see next paragraph for an explanation. The name of the key pair in EC2 will be set to your IAM user account name. In S3 the public key will be stored under its fingerprint.

If cgcloud complains that the Private key file is encrypted, your private key is probably encrypted with a passphrase (as it should). You need to add the key to the SSH agent via ssh-add which should prompt you for the passphrase. On Mac OS X this can be made more convenient by running ssh-add -K or ssh-add -K /path/to/private/key once. This will automatically add the key to the agent every time you log in. The passphrase will be stored in OS X’s key chain so won’t have to enter it again.

Note: Importing your key pair using the EC2 console is not equivalent to cgcloud register-key . In order to be able to manage key pairs within a team, CGCloud needs to know the contents of the public key for every team member’s key pair. But EC2 only exposes a fingerprint via its REST API, not the actual public key. For this purpose, CGCloud maintains those public keys in a special S3 bucket. Using cgcloud register-key makes sure that the public key is imported to EC2 and uploaded to that special S3 bucket. Also note that while that S3 bucket is globally visible and the public keys stored therein apply across regions, the corresponding key pair in EC2 is only visible within a zone. So when you switch to a different region, you will have to use cgcloud register-key again to import the key pair into that EC2 region.

Multi-user SSH logins

By default, CGCloud only injects your public key into the boxes that it creates. This means that only you can SSH into those boxes. If you want other people to be able to SSH into boxes created by you, you can specify a list of key pairs to be injected into boxes. You can do so as using the -k command line option to cgcloud create or by setting the CGCLOUD_KEYPAIRS environment variable. The latter will inject those key pairs by default into every box that you create. The default for -k is the special string __me__ which is substituted with the name of the current IAM user, i.e. you. This only works your IAM user account and your SSH key pair in EC2 have the same name, a practice that is highly recommended. The cgcloud register-key command follows that convention by default.

The most useful shortcut for -k and CGCLOUD_KEYPAIRS however is to list the name of an IAM group by prefixing the group name with @@. Assuming that there exists an IAM group called developers, adding the following line to your .profile or .bash_profile:

export CGCLOUD_KEYPAIRS="__me__ @@developers"

will inject your own key pair and the key pair of every user in the developers IAM group into every box that you create from that point onwards. Obviously, this only works if EC2 key pairs and IAM usernames are identical but as mentioned above, if you used cgcloud register-key this should be the case.

In the above example, if a user is removed from the IAM group developers or if their key pair is deleted from EC2, his or her key pair will be automatically removed from every box that was created with that value of CGCLOUD_KEYPAIRS.

Note that a change to CGCLOUD_KEYPAIRS does not affect boxes created with cgcloud recreate ROLE. You will need to create a new image using cgcloud create -IT ROLE for the change to take effect.

First steps

You’re now ready to create your first box aka EC2 instance or VM:

cgcloud create generic-ubuntu-trusty-box

This creates a Ubuntu Trusty instance from a stock Ubuntu AMI and then further customizes it by running additional commands via SSH. It’ll take a few minutes. The generic-ubuntu-trusty-box argument denotes a role, i.e. a blueprint for an instance. You can use cgcloud list-roles to see the available roles.

Now login to the newly created box:

cgcloud ssh generic-ubuntu-trusty-box

The astute reader will notice that it is not necessary to remember the public hostname assigned to the box. As long as there is only one box per role, you can refer to the box by using the role’s name. Otherwise you will need to disambiguate by specifying an ordinal using the -o option. Use cgcloud list to view all running instances and their ordinals.

Also note that it isn’t necessary to specify the account name of the administrative user to log in as, e.g. ec2-user, root or ubuntu . The stock images for the various Linux distributions use different account names but CGCloud conveniently hides these differences.

In order to copy files to and from the box you can use cgcloud rsync:

cgcloud rsync generic-ubuntu-trusty-box -av ~/mystuff :

The cgcloud rsync command behaves like a prefix to the rsync command with one important difference: With rsync you would specify the remote hostname followed by a colon, with cgcloud rsync you simply leave the hostname blank and only specify a colon followed by the remote path. If you omit the remote path, the home directory of the administrative user will be used.

You can now stop the box with cgcloud stop, start it again using cgcloud start or terminate it using cgcloud terminate. Note while a stopped instance is much cheaper than a running instance, it is not free. Only the terminate command will reduce the operating cost incurred by the instance to zero.

If you want to preserve the modifications you made to the box such that you can spawn another box in the future just like it, stop the box and then create an image of it using the cgcloud image command. You may then use the cgcloud recreate command to bring up a box.

Philosophical remarks

While creating an image is a viable mechanism to preserve manual modifications to a box, it is not the best possible way. The problem with it is that you will be stuck with the base image release the box was created from. You will also be stuck with the customizations performed by the particular version of cgcloud you were using. If either the base image or the role definition in CGCloud is updated, you will not benefit from those updates. Therefore, the preferred way of customizing a box is by scripting the customizations. This is typically done by creating a CGCloud plugin, i.e. a Python package with VM definitions aka roles. A role is a subclass of the Box class while a box (aka VM aka EC2 instance) is an instance of that class. The prominent design patterns formed by Box and its derived classes are Template Method and Mix-in. The mix-in pattern introduces a sensitivity to Python’s method resolution order so you need to be aware of that.

Creating an image makes sense even if you didn’t make any modifications after cgcloud create. It captures all role-specific customizations made by cgcloud create, thereby protecting them from changes in the role definition, the underlying base image and package updates in the Linux distribution used by the box. This is key to CGCloud’s philosophy: It gives you a way to create an up-to-date image with all the latest software according to your requirements and it allows you reliably reproduce the exact result of that step. The fact that recreate is much faster than create is icing on the cake.

Building & Testing

First, clone this repository and cd into it. To run the tests use

  • python nosetests --with-doctest,
  • python test,
  • nosetest or
  • python -m unittest discover -s src.

We prefer the way listed first as it installs all requirements and runs the tests under Nose, a test runner superior to unittest that can run tests in parallel and produces Xunit-like test reports. For example, on continuous integration we use

virtualenv env
env/bin/python nosetests --processes=16 --process-timeout=900

To make an editable install, also known as development mode, use python develop. To remove the editable install python develop -u.


  • If cgcloud create gets stuck repeatedly printing Private key file is encrypted, your private key is probably encrypted with a passphrase (as it should). You need to add the key to the SSH agent via ssh-add which should prompt you for the passphrase. On Mac OS X this can be made more convenient by running ssh-add -K or ssh-add -K /path/to/private/key once. This will automatically add the key to the agent every time you log in. The passphrase will be stored in OS X’s key chain so won’t have to enter it again.

  • If you get the following error:

    ERROR: Exception: Incompatible ssh peer (no acceptable kex algorithm)
    ERROR: Traceback (most recent call last):
    ERROR:   File "/usr/local/lib/python2.7/site-packages/paramiko/", line 1585, in run
    ERROR:     self._handler_table[ptype](self, m)
    ERROR:   File "/usr/local/lib/python2.7/site-packages/paramiko/", line 1664, in _negotiate_keys
    ERROR:     self._parse_kex_init(m)
    ERROR:   File "/usr/local/lib/python2.7/site-packages/paramiko/", line 1779, in _parse_kex_init
    ERROR:     raise SSHException('Incompatible ssh peer (no acceptable kex algorithm)')
    ERROR: SSHException: Incompatible ssh peer (no acceptable kex algorithm)

try upgrading paramiko:

pip install --upgrade paramiko

See also


CGCloud can be customized via plugins. A plugin is a Python module or package containing two functions:

def roles():
   Return a list of roles, each role being a concrete subclass of
   return [ FooBox ]

def command_classes():
   Return a list of command classes, each class being a concrete subclass of
   return [ FooCommand ]

If the plugin is a Python package, these two functions need to be defined in its The box and command classes returned by these two functions can be defined in submodules of that package.

In order to be loaded by CGCloud, a plugin needs to be loadable from sys.path and its module path ( needs to be mentioned in the CGCLOUD_PLUGINS environment variable which should contains a colon-separated list of plugin module paths.

You can also run CGCloud with the --script option and a path to a Python script. The script will be handled like a plugin, except that it should not define a command_classes() function since that function will not be invoked for a script plugin. In other words, a script plugin should only define roles, not commands.

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