Helps manage AWS CloudFormation stacks
|Circle CI|
2014-07-01
- Added colour cloudformation event status output via
'highlight-output' setting in YAML.
::
highlight-output: true
2014-04-17You can now insert PyStache {{}} style variables to import environment variables.
::
stack: ami_id: {{AMIID}}
AMID=ami-1q23123123 cumulus -y example_stack.yaml -a create
would be seen by cloudformation with the ami id of ami-1q23123123
2013-09-06
- You can now define stack level tags using the *tags* directive in the
YaML file, like:
::
tags:
tag1: value
tag2: value
tags can be specified both
at root level and sub-stack level. tags at root level are applied to all
sub-stacks and duplicate sub-stack tags will override root level tags
- You can use the directive ``disable: true`` in any sub-stack to prevent it from being created/updated/deleted
The problem
-----------
Amazon CloudFormation (CF) allows you to instantiate multiple AWS
resources in a repeatable, ordered and structured method. As our
infrastructure grew, so did our CF templates and soon they were
monolothic and complex to maintain. We looked at spliting these
templates into smaller chunks, which worked as a short term solution but
created a new problem. With multiple templates dependant on other
declared resources, we were forced to manually pass parameters for
inter-stack operability. This greatly affected the repeatability of our
stacks as we did not have an easy method to keep track of what
parameters were used, especially those relating to physical resource
IDs.
The solution
------------
Cumulus attempts to solve the problem by introducing a layer above CF
templates, a stack configuration YAML file. This allows multiple CF
stacks to be created in order and maintained respecting their
dependencies. The YAML file stores values for parameters to be passed
into each of the stacks. Parameters can be assigned with static values
or will source the value of a parameter, output or resource of another
stack described in the YAML file. Cumulus actively translates reference
values to physical resource values on creation of the stack.
Current state / known issues
----------------------------
For our use, Cumulus can create, update and delete stacks reliably but
is still very much in an Alpha state. We're looking forward to see how
you use Cumulus, and please submit pull requests for any issues you may
encounter or for feature requests :)
This is my first real python project, so I'm sure the code can be, just
generally better...
Known issues:
- Templates are passed in as a JSON string to CF, this will break large
templates
Roadmap:
- Implement a way of displaying meaningful diffs during update runs
- Add support for using S3/Externally hosted templates
- Support larger templates
How to get started
------------------
Clone the repo somewhere:
::
$ git clone git://github.com/peterkh/cumulus.git
Install Cumulus with setuptools:
::
$ sudo python setup.py install
Make sure you have AWS credentials set up for boto (the library used by
Cumulus to interact with AWS). Set the following environment variables:
**AWS\_ACCESS\_KEY\_ID** - Your AWS Access Key ID
**AWS\_SECRET\_ACCESS\_KEY** - Your AWS Secret Access Key
or create a boto config file as described
`here <http://docs.pythonboto.org/en/latest/boto_config_tut.html>`__, covering some
other helpful boto-related settings.
Creating the example stack
--------------------------
**Common sense warning:** Running this example will create real
resources in AWS and will cost you AWS credits / money / magic beans.
I have included an example stack in the examples/ dir. It consists of
three files:
- cumulus\_example\_stack.yaml: The Cumulus yaml file for the stack.
Creates a stack out of the following two templates in ap-southeast-2
(Sydney region)
- vpc\_layer.json: CF template to creates a VPC, base subnet and ACL
- instance\_layer.json: CF template to create an instance inside a
given VPC
The template files are complete and work independently of Cumulus.
Cumulus's purpose in life is just to make managing them easier.
To create the example stack, change into the examples/ dir and run:
::
$ cumulus -y cumulus_example_stack.yaml -a create
Cumulus will print out CF messages as it builds.
You can then try modifying the template and/or the values of the
parameters and then update the stack:
::
$ cumulus -y cumulus_example_stack.yaml -a update
Once you have finished experimenting, you can delete as follows:
::
$ cumulus -y cumulus_example_stack.yaml -a delete
General usage
-------------
::
cumulus -h
usage: cumulus [-h] -y YAMLFILE -a ACTION [-l LOGLEVEL] [-L BOTOLOGLEVEL]
[-s STACKNAME]
optional arguments:
-h, --help show this help message and exit
-y YAMLFILE, --yamlfile YAMLFILE
The yaml file to read the VPC mega stack configuration
from
-a ACTION, --action ACTION
The action to perform: create, check, update, delete
or watch
-l LOGLEVEL, --log LOGLEVEL
Log Level for output messages, CRITICAL, ERROR,
WARNING, INFO or DEBUG
-L BOTOLOGLEVEL, --botolog BOTOLOGLEVEL
Log Level for boto, CRITICAL, ERROR, WARNING, INFO or
DEBUG
-s STACKNAME, --stack STACKNAME
The stack name, used with the watch action, ignored
for other actions
YAML file format
----------------
Have a look at examples/cumulus\_example\_stack.yaml for a commented
version of the yaml file.
All sections are required at the moment, even if they are blank (i.e.
depends, params). depends also needs to be empty or an array, even if
the stack has only one dependency.
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