# Live Updates Architecture

## Overview

This document describes the live updates architecture for `apt-ostree`, covering how the system handles live updates, user overlays, and runtime modifications without requiring system reboots. The design enables dynamic system updates while maintaining system stability and consistency.

## Live Update Commands

### Core Live Update Commands

#### `apt-ostree apply-live`
Applies live updates to the running system.

**Purpose:**
- Apply package updates without reboot
- Update system configuration
- Modify running services
- Apply security patches

**Implementation Details:**
- Package installation in user space
- Service restart and reload
- Configuration file updates
- Runtime state management

**Example:**
```bash
# Apply live updates
apt-ostree apply-live

# Apply specific package updates
apt-ostree apply-live --packages=nginx,postgresql

# Apply with service restart
apt-ostree apply-live --restart-services
```

**Options:**
- `--packages`: Specific packages to update
- `--restart-services`: Restart affected services
- `--dry-run`: Show what would be updated
- `--force`: Force update even if risky

#### `apt-ostree usroverlay`
Manages user overlays for live modifications.

**Purpose:**
- Create temporary file overlays
- Modify system files at runtime
- Test configuration changes
- Apply temporary fixes

**Implementation Details:**
- Overlay filesystem creation
- File modification tracking
- Change persistence management
- Overlay cleanup and removal

**Example:**
```bash
# Create user overlay
apt-ostree usroverlay --create

# Add file to overlay
apt-ostree usroverlay --add=/etc/nginx/nginx.conf

# Remove overlay
apt-ostree usroverlay --remove
```

**Options:**
- `--create`: Create new overlay
- `--add`: Add file to overlay
- `--remove`: Remove overlay
- `--list`: List overlay contents

## Live Update Architecture

### Overlay Filesystem System

#### Overlay Structure

The live update system uses overlay filesystems:

```
System Structure:
├── Base OSTree (read-only)
├── User Overlay (read-write)
└── Runtime Modifications (temporary)
```

**Components:**
- **Base layer**: Original OSTree deployment
- **User overlay**: Persistent user modifications
- **Runtime layer**: Temporary runtime changes
- **Union mount**: Combined filesystem view

#### Overlay Types

1. **User Overlays**
   - Persistent across reboots
   - User-specific modifications
   - Configuration customizations
   - Package additions

2. **Runtime Overlays**
   - Temporary modifications
   - Service state changes
   - Configuration updates
   - Package installations

3. **System Overlays**
   - System-wide modifications
   - Service configurations
   - Security updates
   - System customizations

### Live Update Process

#### Update Workflow

1. **Update Detection**
   - Check for available updates
   - Validate update compatibility
   - Assess update impact
   - Determine update strategy

2. **Update Preparation**
   - Download update packages
   - Verify package integrity
   - Check dependencies
   - Prepare update environment

3. **Update Application**
   - Apply package updates
   - Update configuration files
   - Restart affected services
   - Update system state

4. **Update Verification**
   - Verify update success
   - Check system stability
   - Validate functionality
   - Update completion status

#### Service Management

**Service Updates:**
- **Configuration updates**: Modify service configs
- **Service restarts**: Restart modified services
- **Dependency updates**: Update service dependencies
- **State management**: Maintain service state

**Update Strategies:**
- **Hot reload**: Reload configuration
- **Graceful restart**: Restart with minimal downtime
- **Full restart**: Complete service restart
- **Rolling update**: Update services incrementally

## User Overlay System

### Overlay Management

#### Overlay Creation

```bash
# Create new overlay
apt-ostree usroverlay --create --name=my-overlay

# Create overlay with specific scope
apt-ostree usroverlay --create --scope=system --name=system-overlay
```

**Overlay Properties:**
- **Name**: Unique overlay identifier
- **Scope**: Overlay scope (user, system, global)
- **Persistence**: Persistence across reboots
- **Priority**: Overlay priority level

#### Overlay Operations

**File Operations:**
- **Add files**: Add files to overlay
- **Modify files**: Modify existing files
- **Remove files**: Remove files from overlay
- **List files**: List overlay contents

**Overlay Management:**
- **Enable/disable**: Control overlay activation
- **Priority adjustment**: Modify overlay priority
- **Cleanup**: Remove unused overlays
- **Backup**: Backup overlay contents

### Overlay Persistence

#### Persistence Strategies

1. **Persistent Overlays**
   - Survive system reboots
   - Stored in persistent storage
   - Maintain user customizations
   - Support long-term modifications

2. **Temporary Overlays**
   - Lost on system reboot
   - Stored in temporary storage
   - Support runtime modifications
   - Enable testing and experimentation

3. **Hybrid Overlays**
   - Selective persistence
   - Configurable persistence rules
   - Automatic cleanup policies
   - Smart persistence management

#### Storage Management

**Storage Locations:**
- **User overlays**: `/var/lib/apt-ostree/overlays/user/`
- **System overlays**: `/var/lib/apt-ostree/overlays/system/`
- **Runtime overlays**: `/tmp/apt-ostree/overlays/`
- **Backup overlays**: `/var/lib/apt-ostree/overlays/backup/`

**Storage Optimization:**
- **Compression**: Compress overlay data
- **Deduplication**: Remove duplicate content
- **Cleanup**: Automatic cleanup policies
- **Archival**: Archive old overlays

## Runtime Modification System

### Dynamic Configuration

#### Configuration Updates

**File Modifications:**
- **Configuration files**: Update service configs
- **System files**: Modify system settings
- **User files**: Update user preferences
- **Temporary files**: Create runtime files

**Update Methods:**
- **Direct modification**: Modify files directly
- **Template application**: Apply configuration templates
- **Variable substitution**: Substitute configuration variables
- **Conditional updates**: Apply updates conditionally

#### Service Management

**Service Updates:**
- **Configuration reload**: Reload service configuration
- **Service restart**: Restart modified services
- **Dependency updates**: Update service dependencies
- **State preservation**: Maintain service state

**Update Coordination:**
- **Dependency ordering**: Order updates by dependency
- **Rolling updates**: Update services incrementally
- **Rollback support**: Support update rollback
- **Health monitoring**: Monitor service health

### State Management

#### Runtime State

**State Components:**
- **Service state**: Current service status
- **Configuration state**: Current configuration
- **Package state**: Installed package state
- **System state**: Overall system state

**State Tracking:**
- **Change tracking**: Track all changes
- **State history**: Maintain state history
- **Rollback points**: Create rollback points
- **State validation**: Validate state consistency

#### State Persistence

**Persistence Methods:**
- **File-based**: Store state in files
- **Database**: Store state in database
- **Memory**: Keep state in memory
- **Hybrid**: Combine multiple methods

**State Synchronization:**
- **Real-time sync**: Synchronize state in real-time
- **Periodic sync**: Synchronize state periodically
- **Event-driven sync**: Synchronize on events
- **Manual sync**: Manual synchronization

## Security Considerations

### Update Security

#### Update Validation

**Security Checks:**
- **Package signatures**: Verify package authenticity
- **Source validation**: Validate update sources
- **Integrity checking**: Check update integrity
- **Compatibility verification**: Verify update compatibility

**Update Policies:**
- **Update approval**: Require update approval
- **Rollback policies**: Define rollback policies
- **Security scanning**: Scan updates for security issues
- **Update testing**: Test updates before application

#### Access Control

**Permission Management:**
- **Update permissions**: Control who can apply updates
- **Overlay permissions**: Control overlay access
- **Service permissions**: Control service modifications
- **Configuration permissions**: Control configuration changes

**Audit Logging:**
- **Update logging**: Log all update operations
- **Change tracking**: Track all system changes
- **Access logging**: Log access to sensitive operations
- **Security events**: Log security-related events

### Runtime Security

#### Overlay Security

**Overlay Protection:**
- **Access control**: Control overlay access
- **Content validation**: Validate overlay content
- **Malware scanning**: Scan overlay content
- **Isolation**: Isolate overlay operations

**Security Policies:**
- **Content policies**: Define allowed content
- **Access policies**: Define access rules
- **Modification policies**: Define modification rules
- **Cleanup policies**: Define cleanup rules

## Performance Optimization

### Update Performance

#### Update Optimization

**Parallel Processing:**
- **Concurrent updates**: Update multiple components concurrently
- **Parallel downloads**: Download updates in parallel
- **Parallel installation**: Install updates in parallel
- **Parallel verification**: Verify updates in parallel

**Caching Strategy:**
- **Update caching**: Cache update data
- **Configuration caching**: Cache configuration data
- **Service caching**: Cache service information
- **State caching**: Cache system state

#### Resource Management

**Resource Optimization:**
- **Memory usage**: Optimize memory usage
- **Disk usage**: Optimize disk usage
- **CPU usage**: Optimize CPU usage
- **Network usage**: Optimize network usage

**Resource Limits:**
- **Memory limits**: Set memory usage limits
- **Disk limits**: Set disk usage limits
- **CPU limits**: Set CPU usage limits
- **Network limits**: Set network usage limits

### Overlay Performance

#### Overlay Optimization

**Storage Optimization:**
- **Compression**: Compress overlay data
- **Deduplication**: Remove duplicate content
- **Efficient storage**: Use efficient storage formats
- **Cleanup policies**: Implement cleanup policies

**Access Optimization:**
- **Caching**: Cache overlay data
- **Indexing**: Index overlay contents
- **Lazy loading**: Load overlay data on demand
- **Prefetching**: Prefetch frequently accessed data

## Error Handling

### Update Errors

#### Common Update Issues

1. **Package Conflicts**
   - Dependency conflicts
   - Version conflicts
   - Architecture conflicts
   - Repository conflicts

2. **Service Issues**
   - Service failures
   - Configuration errors
   - Dependency problems
   - State inconsistencies

3. **System Issues**
   - Disk space problems
   - Permission errors
   - Network issues
   - Resource exhaustion

#### Error Recovery

**Recovery Strategies:**
- **Automatic rollback**: Rollback failed updates
- **Partial recovery**: Recover partial updates
- **Error reporting**: Report detailed error information
- **Recovery guidance**: Provide recovery guidance

**Rollback Mechanisms:**
- **Immediate rollback**: Rollback immediately on failure
- **Deferred rollback**: Rollback after user confirmation
- **Selective rollback**: Rollback specific components
- **Full rollback**: Rollback entire update

### Overlay Errors

#### Overlay Issues

1. **Storage Problems**
   - Disk space issues
   - Permission problems
   - Corruption issues
   - Access problems

2. **Content Issues**
   - Invalid content
   - Malicious content
   - Corrupted content
   - Incompatible content

3. **System Issues**
   - Mount failures
   - Union mount problems
   - Performance issues
   - Stability problems

#### Overlay Recovery

**Recovery Methods:**
- **Content validation**: Validate overlay content
- **Corruption repair**: Repair corrupted overlays
- **Access restoration**: Restore overlay access
- **Performance optimization**: Optimize overlay performance

## Integration Points

### System Integration

#### OSTree Integration

Live updates integrate with OSTree:

- **Deployment management**: Manage OSTree deployments
- **Commit tracking**: Track OSTree commits
- **Rollback support**: Support OSTree rollbacks
- **Metadata management**: Manage OSTree metadata

#### Service Integration

Integration with system services:

- **systemd**: Manage systemd services
- **Service management**: Control service lifecycle
- **Configuration management**: Manage service configuration
- **State management**: Track service state

### User Interface Integration

#### CLI Integration

Command-line interface integration:

- **Command execution**: Execute live update commands
- **Progress reporting**: Report update progress
- **Status display**: Display update status
- **Error reporting**: Report update errors

#### DBus Integration

DBus interface integration:

- **Update signals**: Signal update events
- **Progress signals**: Signal progress updates
- **Status signals**: Signal status changes
- **Error signals**: Signal error conditions

## Future Enhancements

### Planned Features

1. **Advanced Live Updates**
   - Incremental updates
   - Delta updates
   - Smart update scheduling
   - Update prediction

2. **Enhanced Overlays**
   - Overlay templates
   - Overlay inheritance
   - Overlay validation rules
   - Overlay optimization

3. **Performance Improvements**
   - Update acceleration
   - Overlay optimization
   - Resource optimization
   - Caching improvements

4. **Security Enhancements**
   - Enhanced validation
   - Security scanning
   - Access control improvements
   - Audit enhancements

## Implementation Notes

### Current Status

- Basic live update functionality implemented
- User overlay system operational
- Runtime modification support
- Update coordination working

### Next Steps

1. **Advanced Features**
   - Enhanced update system
   - Advanced overlay management
   - Performance optimization
   - Security improvements

2. **Integration Improvements**
   - Enhanced system integration
   - Better service management
   - Improved error handling
   - Enhanced user experience

3. **Testing and Validation**
   - Comprehensive testing
   - Performance testing
   - Security testing
   - Integration testing
