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 :)
That said, at Remind we use stacker to manage all of our Cloudformation stacks- both in development, staging and production without any major issues.
The stacker command is built to have sub-commands, much like git. Currently the
only implemented command is build, which handles taking your stack config
and then launching or updating stacks as necessary.
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, and dns entries in BaseDomain)
- A public, route53 zone (BaseDomain parameter)
- 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 build -v -p BaseDomain=blahblah.com -r us-east-1 conf/stage.env conf/example.yaml
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.
There are multiple ways to define parameters for stacks, each useful in different ways:
- the
-p/--parametercommand 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.
One additional bit of functionality that should be noted is that if a Parameter is defined, but has no value, for example in the stack config like this:
MyParameter:
That parameter will not be submitted to the stack. This allows you to control whether a parameter is submitted to a stack by using environments.
As well as defining the stack config, you'll need to specify an
environment. The environment should point to 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.
At a minimum the environment must define the namespace parameter:
namespace: example.com
The namespace should be a unique name that the stacks will be built under. This value will be used to prefix the CloudFormation stack names as well as the s3 bucket that contains the stacker templates. Specifying the namespace in the environment file helps preserve the namespace for the stacks between subsequent builds.
Stack can also be executed from Docker. Use this method to run stacker if you want to avoid setting up a python environment:
docker run -v `pwd`:/stacks remind101/stacker build ...