hy·gro·scope
ˈhīɡrəˌskōp/, noun
an instrument that gives an indication of the humidity of the air.
Hygroscope is a Thor-based command-line tool for managing the launch of complex CloudFormation stacks.
CloudFormation is a great way to manage infrastructure resources using code, but it has some aspects that make it a pain:
- Templates must be written in JSON, which, in addition to being difficult for a human to read, does not support niceties such as inline comments and repeated blocks.
- Launching CloudFormation stacks requires knowledge of the various parameters that need to be provided, and it is difficult to repeatably launch a stack since parameters are not saved in any convenient way.
- There is no easy mechanism to send a payload of data to an instance during stack creation (for instance scripts and recipes to bootstrap an instance).
- Finally, it is difficult to launch stacks that build upon already-existing stacks (i.e. an application stack within an existing VPC stack) because one must manually provide a variety of identifiers (subnets, IP addresses, security groups).
Hygroscope aims to solve each of these specific problems in an opinionated way:
- CF templates are written in YAML and processed using cfoo, which provides a variety of convenience methods that increase readability.
- Hygroscope can interactively prompt for each parameter and save inputted parameters to a file called a paramset. Additional stack launches can make use of existing paramsets, or can use paramsets as the basis and prompt for updated parameters.
- A payload directory, if present, will be packaged and uploaded to S3. Hygroscope will generate and pass to CF a signed time-limited URL for accessing and downloading the payload, or the CloudFormation template can manage an instance profile granting indefinite access to the payload.
- If an existing stack is specified, its outputs will be fetched and passed through as input parameters when launching a new stack.
Hygroscope can be installed via RubyGems. Run hygroscope help to view inline command documentation and options. See template structure for information about the format of hygroscopic templates.