helmfile/pkg/app/README_RUN.md

Run Struct

Overview

The Run struct is a core component of Helmfile's execution model, responsible for orchestrating the preparation, execution, and cleanup phases of Helmfile commands. It provides a consistent workflow for all Helmfile operations while maintaining separation of concerns.

Core Mechanics

The Preparation-Execution-Cleanup Pattern

At the heart of the Run package is the withPreparedCharts method, which implements a functional programming pattern to standardize how Helmfile commands are executed:

func (r *Run) withPreparedCharts(helmfileCommand string, opts state.ChartPrepareOptions, f func()) error {
    // Preparation phase
    // ...

    // Execution phase
    f()

    // Cleanup phase
    // ...
}

This pattern consists of three distinct phases:

1. Preparation Phase:

   • Validates the current state
   • Syncs repositories if needed
   • Creates temporary directories for chart downloads
   • Triggers global prepare events
   • Downloads and processes charts

2. Execution Phase:

   • Executes the command-specific logic provided as a function parameter
   • Command implementations are decoupled from chart preparation

3. Cleanup Phase:

   • Triggers global cleanup events
   • Handles resource cleanup

Usage Example

Commands like diff, apply, or template use this pattern by providing their specific implementation as a function:

// Example: How the diff command uses withPreparedCharts
err := run.withPreparedCharts("diff", opts, func() {
    msg, matched, affected, errs = a.diff(run, c)
})

Benefits

• Consistent Workflow: All commands follow the same preparation, execution, and cleanup flow
• Separation of Concerns: Chart preparation logic is centralized and reused across commands
• Resource Management: Temporary resources are properly created and cleaned up
• Extensibility: New commands can be added by implementing their specific logic without duplicating preparation code

Key Components

• ReleaseToChart: Maps release identifiers to their prepared chart paths
• Chart Preparation: Handles downloading, modifying, and preparing charts for use
• Repository Synchronization: Ensures all required Helm repositories are available
• Event Triggers: Executes global prepare and cleanup events at appropriate times

Implementation Details

The Run struct maintains state throughout the execution lifecycle, ensuring that charts are prepared only once and that all commands have access to the prepared charts through the ReleaseToChart map.

Commands can focus on their specific implementation while relying on the withPreparedCharts method to handle all the common preparation and cleanup tasks.