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Priority 1 Implementation Summary

Overview

This document summarizes the implementation of Priority 1: Stabilize Core Runtime for the basic-docker-engine project.

Completed Features

1. Cgroup v1/v2 Detection and Graceful Degradation

File: cgroup.go

  • Automatic Detection: The system now automatically detects whether the host is using cgroup v1 (legacy) or v2 (unified hierarchy)
  • Version-Specific Handling:
    • Cgroup v2: Uses /sys/fs/cgroup/cgroup.controllers and memory.max
    • Cgroup v1: Uses /sys/fs/cgroup/memory and memory.limit_in_bytes
  • Controller Detection: Checks for memory and CPU controller availability
  • Graceful Degradation: When cgroups are unavailable:
    • Containers still execute without resource limits
    • Warning messages inform users about degraded functionality
    • No fatal errors - system continues operating

Key Functions:

  • DetectCgroupVersion(): Returns detailed cgroup information
  • SetupCgroupsWithDetection(): Automatically applies correct version
  • CleanupCgroup(): Removes cgroup resources on container removal

2. Container Lifecycle State Management

File: container.go

Implements a complete state model for containers:

States:

  • created - Container directory structure created, metadata initialized
  • running - Container process is executing
  • exited - Container completed successfully (exit code 0)
  • failed - Container terminated with error (non-zero exit code)

State Persistence: Each container has a state.json file in /tmp/basic-docker/containers/<id>/ containing:

{
  "id": "container-123",
  "state": "exited",
  "image": "alpine",
  "command": "/bin/echo",
  "args": ["hello"],
  "created_at": "2025-12-31T10:00:00Z",
  "started_at": "2025-12-31T10:00:01Z",
  "finished_at": "2025-12-31T10:00:02Z",
  "exit_code": 0,
  "pid": 12345,
  "rootfs_path": "/tmp/basic-docker/containers/container-123/rootfs"
}

Key Functions:

  • SaveContainerState(): Persists metadata to disk
  • LoadContainerState(): Loads metadata from disk
  • UpdateContainerState(): Atomic state updates
  • ListAllContainers(): Returns all containers with states
  • RemoveContainer(): Safely removes stopped containers
  • GetContainerLogs(): Retrieves container output

3. New CLI Commands

Updated: main.go

rm <container-id>

  • Removes stopped containers and their resources
  • Safety check: prevents removal of running containers
  • Cleans up cgroup directories
  • Removes container filesystem and metadata

logs <container-id>

  • Displays stdout/stderr from containers
  • Reads from persistent log files
  • Works for both running and stopped containers

inspect <container-id>

  • Shows detailed container information in JSON format
  • Includes all metadata fields
  • Useful for debugging and automation

Updated info command

  • Now displays cgroup version (v1/v2)
  • Shows memory and CPU controller availability
  • Indicates base cgroup path
  • Lists all available features with proper status

Updated ps command

  • Shows container states instead of generic "status"
  • Displays created timestamps
  • Better formatted output

4. Enhanced Logging

Improvement: io.MultiWriter

Container output now goes to both:

  1. Console (stdout/stderr) - for immediate visibility
  2. Log file (/tmp/basic-docker/containers/<id>/stdout.log) - for persistence

Benefits:

  • Users see output in real-time
  • Logs are preserved for later inspection
  • No tradeoff between visibility and persistence

5. Testing & Verification

New File: container_test.go

Comprehensive unit tests covering:

  • Cgroup version detection
  • Container state save/load/update
  • Container listing
  • Container removal (with safety checks)
  • Log retrieval

All tests pass on cgroup v2 systems.

New File: verify-new.sh

Structured verification script with:

  • Color-coded output (success/error/info)
  • Clear test sections
  • Automatic binary validation
  • Proper error handling
  • Test result counting
  • 12 comprehensive test cases

Test Coverage:

  1. System information & cgroup detection
  2. Test image creation
  3. Container lifecycle - run command
  4. List containers (ps)
  5. Inspect container
  6. Container logs
  7. Failed container state
  8. Remove container (rm)
  9. Safety checks
  10. Help command
  11. Network commands
  12. Cgroup cleanup

6. Documentation

Updated: README.md

New sections:

  • Project scope and goals
  • Core features overview
  • Prerequisites
  • Container lifecycle documentation
  • Cgroup support explanation
  • Usage examples for all new commands
  • Graceful degradation explanation

Technical Improvements

Code Quality

  • DRY Principle: Removed duplicate command/args extraction
  • Error Visibility: Added warning logs instead of silent failures
  • Resource Management: Proper cleanup with cgroup removal
  • Type Safety: Strong typing for container states
  • Atomicity: Atomic state updates via UpdateContainerState

Security

  • CodeQL Clean: No security vulnerabilities detected
  • Permission Checks: Cannot remove running containers
  • Graceful Handling: No panics on permission errors

User Experience

  • Informative Output: Clear status messages
  • Help Text: Updated with all commands
  • Error Messages: Descriptive and actionable
  • Logging: Both real-time and persistent

Testing Results

Unit Tests

PASS: TestDetectCgroupVersion
PASS: TestSaveAndLoadContainerState
PASS: TestUpdateContainerState
PASS: TestListAllContainers
PASS: TestRemoveContainer
PASS: TestGetContainerLogs

Integration Tests (verify-new.sh)

All 12 test sections pass successfully.

Security Scan

CodeQL: 0 vulnerabilities found

Files Modified/Created

New Files

  1. cgroup.go - Cgroup detection and management (5209 bytes)
  2. container.go - Container lifecycle management (4885 bytes)
  3. container_test.go - Comprehensive unit tests (9208 bytes)
  4. verify-new.sh - Structured verification script (7111 bytes)

Modified Files

  1. main.go - CLI integration, improved commands, MultiWriter
  2. README.md - Comprehensive documentation updates

Impact

Stability Improvements

  • ✅ Containers work on both cgroup v1 and v2 systems
  • ✅ No fatal errors when cgroups unavailable
  • ✅ Proper state tracking prevents data loss
  • ✅ Safety checks prevent accidental data deletion

Feature Completeness

  • ✅ Full container lifecycle management
  • ✅ Persistent logs and metadata
  • ✅ Complete CLI surface for basic operations
  • ✅ Informative system status reporting

Developer Experience

  • ✅ Clear code structure with separate modules
  • ✅ Comprehensive test coverage
  • ✅ Detailed documentation
  • ✅ Easy to verify and debug

Future Considerations

While Priority 1 is complete, future enhancements could include:

  1. Container lifecycle: Add stop and kill commands
  2. Log management: Log rotation and size limits
  3. Restart policies: Auto-restart on failure
  4. Health checks: Container health monitoring
  5. Port mapping: Network port forwarding
  6. Volume support: Persistent data volumes

Conclusion

Priority 1 has been successfully implemented and tested. The core runtime is now stable, with proper cgroup support, complete lifecycle management, and comprehensive CLI commands. The system gracefully handles different environments and provides clear feedback to users.

All acceptance criteria have been met:

  • ✅ Cgroup v1/v2 detection and handling
  • ✅ Container state model with persistence
  • ✅ New CLI commands (rm, logs, inspect)
  • ✅ Comprehensive testing
  • ✅ Updated documentation
  • ✅ Security validation (CodeQL)

The project is ready for the next priorities in the roadmap.