cfnparams 0.2

CloudFormation stack paramater utility.

A CloudFormation stack parameter utility.

Installation

Install via pip:

pip install cfnparams
which cfn-params

Motivation

cfn-params overcomes some limitations of the AWS CLI when handling stack paramaters, such as:

• Simultaneously specifying both parameter arguments and parameter files, e.g. --parameters ParameterKey=foo,ParameterValue=bar --parameters file://params.json

• Overly verbose JSON format

Features

Parameters can be:

• specified on the CLI

• specified in the AWS CLI JSON format

• specified as Python dictionaries

• resolved from the outputs of other stacks

Parameter Specification

Command Line

The same format as the AWS CLI is supported, however you must specify each parameter in its own argument e.g.:

--parameters ParameterKey=foo,ParameterValue=bar --parameters ParameterKey=baz,ParameterValue=quux

JSON files

The same format as the AWS CLI is supported, with the ability to specify as many input files as you like, e.g.:

--parameters file://path/to/params.json

Python dictionaries

Specified the same way JSON files are, but must have the extension .py:

--parameters file://path/to/params.py

e.g.:

{
    # Values must be strings as required by CFN
    'Key': 'Value',

    # All Python builtins are available:
    'FortyTwo': str(6 * 7),
    'MyCommaDelimitedList': ', '.join(['hello', 'world']),
}

Output parameter resolution

When using the Python parameter format, a local method GetOutput(stack, output) is available for use, e.g.:

{
    'foo': GetOutput('other-stack', 'foo'),
}

Stack lookup and resolution

If a dependent stack is referenced in a parameter, cfn-params will use the DescribeStacks API to resolve the parameter from the list of stack outputs.

The lookup process will:

1. Attempt to find a stack with the exact name specified

2. Optionally, use --resolve-tags to filter existing stack to find a fallback match.

The --resolve-tags argument is a list of tag key/value pairs to filter by.

e.g. if you want to only look for stacks in your staging environment:

--resolve-tags Key=Environment,Value=staging