skybridge/faas/IMPLEMENTATION.md

Skybridge FaaS Implementation Guide

This document explains the implementation of the Function-as-a-Service (FaaS) component in Skybridge, specifically focusing on the Docker runtime implementation that replaced the original mock implementation.

Overview

The Skybridge FaaS platform allows users to deploy and execute functions in isolated containers. The implementation consists of several key components:

1. Function Management: CRUD operations for function definitions
2. Execution Engine: Runtime backend for executing functions
3. Repository Layer: Data persistence for functions and executions
4. Services Layer: Business logic implementation
5. API Layer: RESTful interface for managing functions

Docker Runtime Implementation

The original implementation contained a mock Docker runtime (faas/internal/runtime/docker/simple.go) that didn't actually interact with Docker. The new implementation provides real container execution capabilities.

Key Features Implemented

1. Real Docker Client Integration: Uses the official Docker client library to communicate with the Docker daemon
2. Container Lifecycle Management: Creates, starts, waits for, and cleans up containers
3. Image Management: Pulls images when they don't exist locally
4. Resource Limiting: Applies memory limits to containers
5. Input/Output Handling: Passes input to functions and captures output
6. Logging: Retrieves container logs for debugging
7. Health Checks: Verifies Docker daemon connectivity

Implementation Details

Container Creation

The createContainer method creates a Docker container with the following configuration:

• Environment Variables: Function environment variables plus input data
• Resource Limits: Memory limits based on function configuration
• Attached Streams: STDOUT and STDERR for log capture

Function Execution Flow

1. Container Creation: Creates a container from the function's Docker image
2. Container Start: Starts the container execution
3. Wait for Completion: Waits for the container to finish execution
4. Result Collection: Gathers output, logs, and execution metadata
5. Cleanup: Removes the container to free resources

Error Handling

The implementation includes comprehensive error handling:

• Connection Errors: Handles Docker daemon connectivity issues
• Container Errors: Manages container creation and execution failures
• Resource Errors: Handles resource constraint violations
• Graceful Cleanup: Ensures containers are cleaned up even on failures

Testing

Unit Tests

Unit tests are located in faas/test/integration/ and cover:

• Docker runtime health checks
• Container creation and execution
• Error conditions

Example Function

An example "Hello World" function is provided in faas/examples/hello-world/ to demonstrate:

• Function structure and implementation
• Docker image creation
• Local testing
• Deployment to Skybridge FaaS

Deployment

Prerequisites

1. Docker daemon running and accessible
2. Docker socket mounted to the FaaS service container (as shown in docker-compose.yml)
3. Required permissions to access Docker

Configuration

The FaaS service reads configuration from environment variables:

• FAAS_DEFAULT_RUNTIME: Should be set to "docker"
• Docker socket path: Typically /var/run/docker.sock

Security Considerations

The current implementation has basic security features:

• Container Isolation: Functions run in isolated containers
• Resource Limits: Prevents resource exhaustion
• Image Verification: Only pulls trusted images

For production use, consider implementing:

• Container user restrictions
• Network isolation
• Enhanced logging and monitoring
• Authentication and authorization for Docker operations

Performance Optimizations

Potential performance improvements include:

• Image Caching: Pre-pull commonly used images
• Container Pooling: Maintain a pool of ready containers
• Parallel Execution: Optimize concurrent function execution
• Resource Monitoring: Track and optimize resource usage

Future Enhancements

Planned enhancements include:

1. Multiple Runtime Support: Add support for Podman and other container runtimes
2. Advanced Resource Management: CPU quotas, disk limits
3. Enhanced Monitoring: Detailed metrics and tracing
4. Improved Error Handling: More granular error reporting
5. Security Hardening: Additional security measures for container execution

API Usage

The FaaS API provides endpoints for:

• Function Management: Create, read, update, delete functions
• Deployment: Deploy functions to prepare for execution
• Execution: Execute functions synchronously or asynchronously
• Monitoring: View execution status, logs, and metrics

Refer to the API documentation endpoint (/api/docs) for detailed information.