$ show envato/stack_master
StackMaster is a mature Ruby CLI gem for managing AWS CloudFormation stacks. It provides a rich command set (apply, diff, drift, delete, events, outputs, resources, status, validate, lint, nag, compile, tidy, init) and supports multiple template formats (JSON, YAML, ERB, SparkleFormation DSL, CfnDsl) through a pluggable compiler registry. A standout feature is the parameter resolution pipeline: 13+ pluggable resolvers (SSM Parameter Store, ACM certificates, AMI finders, stack outputs, 1Password, EJSON, environment variables, security groups, SSO group IDs) that fetch values at apply/compile time, making cross-account and cross-region stack composition practical. The architecture is cleanly modular — commands are standalone classes sharing a base module, template compilers and parameter resolvers are registered via simple registry interfaces, and the stack event streamer provides live sync feedback during updates. The codebase demonstrates solid engineering craftsmanship: a custom Erubis subclass generates CloudFormation Fn::Join arrays from ERB templates, a role assumer caches STS credentials per (account, role) and temporarily swaps Aws.config to support cross-account operations, and a generic PagedResponseAccumulator cleanly handles AWS SDK pagination. Test coverage is extensive — RSpec unit specs plus Cucumber/Aruba feature tests exercise every command and resolver against stubbed AWS responses, and a dedicated in-memory test driver (TestDriver::CloudFormation/S3) enables isolated testing without network calls. The changelog is meticulously maintained with per-release notes, and the gem supports a wide Ruby range (2.4–4.0). However, there are signs of accumulated technical debt: a large .rubocop_todo.yml exclusions list indicates code quality lapses, the codebase relies on autoload (deprecated in Ruby 3.2+), and heavy stubbing in tests may mask real AWS API integration regressions. Dependency pins on SparkleFormation (~> 3) and CfnDsl (~> 1) could become brittler as those upstream libraries evolve. This is a maintainer-mode tool — stable, well-documented, and battle-tested, but not rapidly evolving.
The LLM identified 4 files worth highlighting for reuse:
Assumes IAM roles via STS, caches credentials per (account, role) pair, and temporarily swaps Aws.config from the calling context. This is a self-contained, isolated component that any Ruby tool needing cross-account AWS access could extract — it handles credential expiry, thread-safe caching, and clean restoration of global config. Demonstrates a robust pattern for multi-account AWS automation without coupling to StackMaster's stack concepts.
Base class and registry for parameter resolvers. It defines a simple `resolve(value)` interface and a class-level `array_resolver` factory that auto-generates plural resolvers from singular implementations. This is a generically reusable strategy/registry pattern — any tool needing pluggable value-resolution from heterogeneous sources (SSM, env vars, APIs, secret vaults) could replicate this design wholesale. The auto-generated array resolver is a clever DRY trick.
A custom Erubis subclass that intercepts Ruby expression interpolation in ERB templates and produces CloudFormation Fn::Join-compatible arrays instead of concatenated strings. This is non-obvious template-engineering craftsmanship — solving a real problem (CloudFormation user-data interpolation needs explicit Fn::Join nodes) with a minimal, elegant extension to the templating engine. Extractable as a standalone utility for any CloudFormation template generator using ERB.
A generic helper that accumulates paginated AWS SDK responses across multiple API calls, handling pagination tokens, max-limits, and normalized result merging. Completely isolated and dependency-free (only requires the AWS SDK), this could be dropped into any Ruby AWS project that needs to page through large result sets (EC2 instances, stack events, S3 objects) without boilerplate. Demonstrates a clean, reusable solution to a ubiquitous AWS SDK annoyance.