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Introduction to YAML Overlay Tool

YAML Overlay Tool (Yot) is not a traditional text-based templating tool. Yot operates on structured YAML nodes. Yot is a YAML overlay or patching tool that primarily takes fragments of YAML configuration from within a declaritive specification to modify and manipulate an existing YAML configuration (manifest).

Each overlay operation is performed with a JSONPath query, a desired value, and an action. If a JSONPath query returns no results, a desired value is either ignored (default behavior), or injected (onMissing). Yot can also provide a specific path or set of paths (injectPath) to inject the value if the initial JSONPath query was not a fully-qualified JSONPath (e.g. using wildcards in the JSONPath query).

Table of contents

1. YAML Overlay Tool features
2. Installation and setup
   • Configuration file
   • Environment variables
3. Command line interface usage and overview
   • Example CLI usage
4. Instructions file introduction
   • Instructions file YAML specification
     • Instructions file usage example
   • Overlay actions
   • Overlay qualifiers
   • Format markers
   • Comment preservation and injection
   • Using templating within instructions files
5. Order of operations/processing order
6. Output directory structure
7. Common use-cases and patterns for Kubernetes
8. Interactive tutorials

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