stacker 0.4.1

Opinionated AWS CloudFormation Stack manager

About

stacker is a tool and library used to create & update multiple CloudFormation stacks. It was originally written at Remind and released to the open source community.

stacker StackTemplates are written in troposphere, though the purpose of most templates is to keep them as generic as possible and then use configuration (and CloudFormation Parameters/Outputs) to modify them.

At this point this is very much alpha software - it is still in heavy development, and interfaces/configuration/etc may/will likely/most definitely change :)

Example

We’ve provided an example stack in conf/example.yaml that can be launched in your account. It creates 4 stacks:

• A VPC (including NAT hosts in each AZ)

• A bastion stack (for ssh’ing into other stacks on the VPC)

• A RDS stack (postgres)

• An autoscaling group stack

The size of most of these is m3.medium, but you can change that in the config if you’d like to play with something smaller. To launch the stacks, after installing stacker and loading your AWS API keys in your environment (AWS_ACCESS_KEY_ID & AWS_SECRET_ACCESS_KEY), call the following:

stacker -v -p BaseDomain=example.com -r us-east-1 -p AZCount=2 -p CidrBlock=10.128.0.0/16 example.com conf/example.yaml

Here’s the syntax help from the command:

# stacker -h
usage: stacker [-h] [-r REGION] [-m MAX_ZONES] [-v] [-p PARAMETER=VALUE]
               [--stacks STACKNAME]
               namespace config

Launches or updates cloudformation stacks based on the given config. The
script is smart enough to figure out if anything (the template, or parameters)
has changed for a given stack. If not, it will skip that stack. Can also pull
parameters from other stack's outputs.

positional arguments:
  namespace             The namespace for the stack collection. This will be
                        used as the prefix to the cloudformation stacks as
                        well as the s3 bucket where templates are stored.
  config                The config file where stack configuration is located.
                        Must be in yaml format.

optional arguments:
  -h, --help            show this help message and exit
  -r REGION, --region REGION
                        The AWS region to launch in. Default: us-east-1
  -m MAX_ZONES, --max-zones MAX_ZONES
                        Gives you the ability to limit the # of zones that
                        resources will be launched in. If not given, then
                        resources will be launched in all available
                        availability zones.
  -v, --verbose         Increase output verbosity. May be specified up to
                        twice.
  -p PARAMETER=VALUE, --parameter PARAMETER=VALUE
                        Adds parameters from the command line that can be used
                        inside any of the stacks being built. Can be specified
                        more than once.
  --stacks STACKNAME    Only work on the stacks given. Can be specified more
                        than once. If not specified then stacker will work on
                        all stacks in the config file.

As of now there is no option to tear down the stack in the tool (we plan to add it), so you’ll need to tear the stacks it creates down manually. When doing so, it’s important that you tear down all the stacks BUT the VPC stack first, since they all depend on the VPC stack. Once they are torn down, you can safely tear down the VPC stack. If you try deleting them all (including VPC) in one swoop, you’ll see that VPC stack gets hung up while waiting for the others to tear down.

Defining Parameters

There are multiple ways to define parameters for stacks, each useful in different ways:

• the -p/--parameter command line argument

• in the stack config

• from an existing stack

Each of those overrides similarly named parameters beneath it, so if you use -p CidrBlock on the command line, it doesn’t matter what is in the config file or any existing stacks. This is useful if, for example, you want to keep sensitive information (passwords, etc) out of the config file (which you’ll likely check into a RCS), but need a way to supply them.

When updating an existing stack, if you don’t supply a parameter in either the config or CLI, it will fall back on checking the existing stack for the parameter. If it finds it, it will use that automatically.

Environments

As well as definining the stack config, you can further customize the stack config via an environment (ie the -e or --environment argument).

The environment should point at a yaml formatted file that contains a flat dictionary (ie: only key: value pairs). Those keys can be used in the stack config as python string.Template mappings.

For example, if you wanted to name a stack based on the environment you were building it in, first you would create an environment file with the environment name in it (staging in this case):

environment: stage

Then, in the stack definition for the stack you are modifying (say the vpc stack), you would have the following:

- name: ${environment}VPC

Stacker would then name the VPC stack stageVPC.