# Executor Service Foundation - Session Summary
**Date**: 2026-01-16 Evening  
**Phase**: Phase 4.1 - Executor Foundation  
**Status**: Core structure complete, needs API refinements

---

## Overview

Implemented the foundational structure for the **Executor Service**, the core orchestration engine of Attune. The Executor is responsible for processing enforcements from triggered rules, scheduling executions to workers, managing execution lifecycle, and enforcing policies.

This session focused on **Session 1: Foundation** as outlined in the implementation plan.

---

## Accomplishments

### 1. Executor Crate Structure Created ✅

Created complete directory structure:
```
crates/executor/
├── Cargo.toml                    # Dependencies configured
└── src/
    ├── main.rs                   # Service entry point
    ├── service.rs                # Main service orchestration
    ├── enforcement_processor.rs  # Enforcement message processing
    ├── scheduler.rs              # Execution scheduling
    └── execution_manager.rs      # Execution lifecycle management
```

### 2. ExecutorService Implementation ✅

**File**: `crates/executor/src/service.rs`

- **Core Features**:
  - Database pool integration (PostgreSQL via SQLx)
  - Message queue connection (RabbitMQ via lapin)
  - Publisher and Consumer initialization
  - Graceful shutdown handling with broadcast channel
  - Cloneable service for sharing across async tasks

- **Architecture**:
  - Uses `Arc<ExecutorServiceInner>` pattern for thread-safe sharing
  - Spawns multiple processor tasks concurrently
  - Handles SIGINT for graceful shutdown

### 3. EnforcementProcessor Module ✅

**File**: `crates/executor/src/enforcement_processor.rs`

- **Purpose**: Processes `EnforcementCreated` messages when rules trigger
- **Responsibilities**:
  - Listen for enforcement messages from RabbitMQ
  - Fetch enforcement, rule, and event data from database
  - Evaluate rule conditions (skeleton implemented)
  - Create execution records
  - Publish `ExecutionRequested` messages

- **Key Components**:
  - `EnforcementCreatedPayload` struct for message deserialization
  - `ExecutionRequestedPayload` struct for outbound messages
  - Database repository integration
  - Message envelope handling

### 4. ExecutionScheduler Module ✅

**File**: `crates/executor/src/scheduler.rs`

- **Purpose**: Routes executions to available workers
- **Responsibilities**:
  - Listen for `ExecutionRequested` messages
  - Fetch action metadata to determine runtime requirements
  - Select appropriate worker based on:
    - Runtime compatibility
    - Worker status (active only)
    - Load balancing (placeholder for future enhancement)
  - Update execution status to `Scheduled`
  - Queue execution to worker-specific queue

- **Worker Selection Strategy**:
  - Filters by runtime compatibility
  - Filters by worker status (active only)
  - Currently selects first available (TODO: implement load balancing)

### 5. ExecutionManager Module ✅

**File**: `crates/executor/src/execution_manager.rs`

- **Purpose**: Manages execution lifecycle and status transitions
- **Responsibilities**:
  - Listen for `ExecutionStatusChanged` messages
  - Update execution records in database
  - Handle workflow orchestration (parent-child executions)
  - Trigger child executions on parent completion
  - Publish completion notifications

- **Status Handling**:
  - Supports all execution states: Requested, Scheduling, Scheduled, Running, Completed, Failed, Cancelled, Timeout, Abandoned
  - Special handling for terminal states (Completed, Failed, Cancelled)
  - Workflow triggering on successful completion

### 6. Service Entry Point ✅

**File**: `crates/executor/src/main.rs`

- **Features**:
  - CLI argument parsing with clap
  - Configurable log level
  - Enhanced logging with thread IDs and line numbers
  - Configuration loading from YAML files
  - Connection string masking for security
  - Graceful shutdown signal handling
  - Comprehensive startup logging

### 7. Dependencies Configured ✅

**File**: `crates/executor/Cargo.toml`

Added dependencies:
- `attune-common` - Shared models, repositories, message queue
- `tokio` - Async runtime
- `sqlx` - Database access
- `serde`, `serde_json` - Serialization
- `tracing`, `tracing-subscriber` - Logging
- `anyhow`, `thiserror` - Error handling
- `config` - Configuration management
- `chrono` - Timestamps
- `uuid` - Message IDs
- `clap` - CLI parsing
- `lapin` - RabbitMQ client
- `redis` - Redis client (for future use)

---

## Technical Details

### Message Flow Architecture

```
1. Enforcement Created:
   sensor → trigger → event → rule → enforcement
   ↓
   EnforcementProcessor listens on "enforcement.created"
   ↓
   Creates Execution record
   ↓
   Publishes "execution.requested" message

2. Execution Scheduling:
   ExecutionScheduler listens on "execution.requested"
   ↓
   Selects appropriate worker
   ↓
   Updates execution status to Scheduled
   ↓
   Publishes to worker-specific queue

3. Execution Lifecycle:
   ExecutionManager listens on "execution.status.*"
   ↓
   Updates execution state in database
   ↓
   On completion: triggers child executions if needed
   ↓
   Publishes "execution.completed" notification
```

### Message Envelope Pattern

All messages use `MessageEnvelope<T>` pattern:
- `message_id`: Unique UUID
- `correlation_id`: For tracing related messages
- `message_type`: Enum for routing
- `timestamp`: Creation time
- `headers`: Metadata (source, trace_id, retry_count)
- `payload`: Typed payload struct

### Database Integration

Uses repository pattern for all database access:
- `EnforcementRepository` (from event module)
- `EventRepository`
- `RuleRepository`
- `ExecutionRepository`
- `ActionRepository`
- `RuntimeRepository`
- `WorkerRepository`

---

## Known Issues & TODOs

### Compilation Issues (To be resolved in Session 2)

1. **Consumer API Pattern Mismatch**:
   - Current code attempts to use `consumer.consume()` method
   - Actual API uses `consumer.consume_with_handler()` pattern
   - Need to refactor processors to use handler-based approach

2. **Missing Trait Implementations**:
   - `WorkerRepository` needs `List` trait implementation
   - `UpdateExecutionInput` needs `From<Execution>` conversion

3. **Unused Imports**:
   - Several modules have unused imports to clean up
   - Minor warnings from dead code

### Future Enhancements (Later Sessions)

1. **Policy Enforcement**:
   - Rate limiting logic
   - Concurrency control
   - Queue management for policy violations

2. **Workflow Orchestration**:
   - Parse workflow definitions from action metadata
   - Extract child actions from execution results
   - Implement DAG-based workflow execution

3. **Inquiry Handling**:
   - Pause executions waiting for human input
   - Handle inquiry timeouts
   - Resume execution with inquiry response

4. **Worker Selection**:
   - Implement intelligent load balancing
   - Consider worker affinity (same pack, same runtime)
   - Geographic locality
   - Round-robin or least-connections strategy

5. **Error Handling**:
   - Retry logic with exponential backoff
   - Dead letter queue for failed messages
   - Circuit breaker pattern for service protection

6. **Monitoring**:
   - Metrics collection
   - Health checks
   - Performance tracking

---

## Testing Strategy

### Unit Tests (To be implemented)
- Enforcement condition evaluation
- Worker selection logic
- Status transition validation
- Message serialization/deserialization

### Integration Tests (To be implemented)
- End-to-end enforcement → execution flow
- Database transaction handling
- Message queue reliability
- Multiple processors running concurrently

### Manual Testing (To be implemented)
- Service startup and shutdown
- Configuration loading
- Graceful shutdown handling
- Message processing throughput

---

## Documentation Updates

### Updated Files
- `work-summary/TODO.md` - Added Session 1 completion, updated priorities
- This session summary document

### Technical Documentation (To be created)
- Architecture diagrams for message flow
- Sequence diagrams for enforcement processing
- Worker selection algorithm documentation
- Configuration examples for production deployment

---

## Metrics

- **Files Created**: 5 new files
- **Lines of Code**: ~1,200 lines
- **Modules Implemented**: 4 core modules
- **Dependencies Added**: 12 crates
- **Compilation Status**: Core structure complete, API refinements needed
- **Test Coverage**: 0% (to be implemented in Session 2)

---

## Next Steps (Session 2: Enforcement Processing)

### Immediate Priorities

1. **Fix Consumer API Usage**:
   - Refactor all processors to use `consume_with_handler` pattern
   - Update message handling to be callback-based
   - Test message consumption

2. **Implement Missing Traits**:
   - Add `List` implementation to `WorkerRepository`
   - Add conversion trait for `UpdateExecutionInput`

3. **Clean Up Warnings**:
   - Remove unused imports
   - Fix dead code warnings

4. **End-to-End Testing**:
   - Create test enforcement in database
   - Verify message flow through all processors
   - Validate execution creation and scheduling

### Medium-Term Goals

5. **Policy Enforcement**:
   - Implement rate limiting checks
   - Add concurrency control
   - Queue management

6. **Workflow Support**:
   - Parse workflow definitions
   - Implement child execution triggering
   - Handle complex execution graphs

7. **Production Readiness**:
   - Add comprehensive error handling
   - Implement retry logic
   - Add monitoring and metrics

---

## Lessons Learned

1. **Message Queue Patterns**: The RabbitMQ library (lapin) uses a handler-based consumption pattern rather than polling. Future code should follow this pattern from the start.

2. **Type Safety**: Using strongly-typed payload structs with `MessageEnvelope<T>` provides excellent type safety and makes message handling more reliable.

3. **Configuration Complexity**: Multiple configuration types (`Config` vs `MessageQueueConfig`) can cause confusion. Need clear documentation on which to use where.

4. **Repository Pattern**: The repository abstraction works well for database access but needs consistent trait implementations across all repositories.

5. **Service Architecture**: The cloneable service pattern with `Arc<ServiceInner>` works well for sharing state across async tasks while maintaining thread safety.

---

## Conclusion

**Session 1 successfully established the foundation for the Executor Service**. The core structure is in place with proper separation of concerns across three main processors (Enforcement, Scheduling, Management). While compilation issues need to be resolved, the architectural decisions are sound and the codebase is well-positioned for rapid iteration in Session 2.

The Executor is now ready to move from foundation to functional implementation, with the message consumption pattern being the primary blocker to overcome.

**Session 1 Status**: ✅ **COMPLETE** (with known issues to address in Session 2)