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faas/IMPLEMENTATION.md

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+# 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.