Function Runner Functionality on Porch Documentation

Function Evaluation

Mon, 01 Jan 0001 00:00:00 +0000

Overview

Function evaluation is the core responsibility of the Function Runner - executing KRM (Kubernetes Resource Model) functions through pluggable evaluator strategies. The system uses a strategy pattern where different evaluators handle function execution in different ways (pod-based, executable, or chained), all conforming to a common interface.

High-Level Architecture

┌─────────────────────────────────────────────────────────┐
│ Function Evaluation System │
│ │
│ ┌──────────────────┐ ┌──────────────────┐ │
│ │ Evaluator │ │ Execution │ │
│ │ Interface │ ───> │ Strategies │ │
│ │ │ │ │ │
│ │ • Common │ │ • Pod Evaluator │ │
│ │ Contract │ │ • Exec Evaluator│ │
│ │ • Pluggable │ │ • Multi Eval │ │
│ └──────────────────┘ └──────────────────┘ │
│ │ │ │
│ └────────┬────────────────┘ │
│ ↓ │
│ ┌──────────────────┐ │
│ │ Wrapper │ │
│ │ Server │ │
│ │ │ │
│ │ • gRPC Frontend │ │
│ │ • Binary Exec │ │
│ │ • Result Parse │ │
│ └──────────────────┘ │
└─────────────────────────────────────────────────────────┘

Evaluator Interface

All evaluators implement a common interface that defines the contract for function execution.

Pod Lifecycle Management

Mon, 01 Jan 0001 00:00:00 +0000

Overview

Pod lifecycle management orchestrates the complete lifecycle of function execution pods from creation through caching, reuse, and eventual garbage collection. The system maintains a pool of ready-to-use pods for frequently executed functions while automatically cleaning up unused pods based on time-to-live policies.

The architecture consists of two primary components:

Pod Cache Manager - Central coordinator running in a single goroutine that manages the pod cache, handles evaluation requests, processes pod readiness notifications, and performs periodic garbage collection. Uses channels for all communication to eliminate mutex synchronization.

Image and Registry Management

Mon, 01 Jan 0001 00:00:00 +0000

Overview

The Function Runner manages container image metadata and registry authentication to optimize pod creation and support private registries. The system caches image metadata (digest and entrypoint) to avoid repeated registry calls, handles authentication for private registries using Docker config format, and supports TLS configuration for secure registry connections.

High-Level Architecture

┌──────────────────────────────────────────────────────────┐
│ Image and Registry Management │
│ │
│ ┌──────────────────┐ ┌──────────────────┐ │
│ │ Image │ │ Registry │ │
│ │ Metadata │ ───> │ Authentication │ │
│ │ Caching │ │ │ │
│ │ │ │ • Default │ │
│ │ • Digest │ │ • Custom Auth │ │
│ │ • Entrypoint │ │ • TLS Config │ │
│ │ • In-Memory │ │ │ │
│ └──────────────────┘ └──────────────────┘ │
│ │ │ │
│ └────────┬────────────────┘ │
│ ↓ │
│ ┌───────────────────┐ │
│ │ Secret │ │
│ │ Management │ │
│ │ │ │
│ │ • Creation │ │
│ │ • Synchronization│ │
│ │ • Pod Injection │ │
│ └───────────────────┘ │
└──────────────────────────────────────────────────────────┘

Image Metadata Caching

The pod manager caches image metadata to avoid repeated registry API calls during pod creation.