# NATS to RabbitMQ Migration Summary

## Migration Overview

Successfully migrated the jobs-scraper project from NATS JetStream to RabbitMQ message queue system.

## Changes Made

### 1. Dependencies Updated
- **Removed**: `github.com/nats-io/nats.go v1.46.1`
- **Added**: `github.com/rabbitmq/amqp091-go v1.10.0`
- **Cleaned up**: Removed NATS-related indirect dependencies (`nats-io/nkeys`, `nats-io/nuid`)

### 2. Infrastructure Changes
- **Directory**: Renamed `infrastructure/nats/` → `infrastructure/rabbitmq/`
- **File**: Renamed `nats.go` → `rabbitmq.go`
- **Client**: `NatsClient` → `RabbitMQClient`

### 3. RabbitMQ Implementation Features

#### Message Queue Architecture
- **Main Exchange**: `scraper_exchange` (topic exchange)
- **Dead Letter Exchange**: `scraper_dlx` (direct exchange)
- **Queues**: 
  - `scraper.linkedin`
  - `scraper.indeed` 
  - `scraper.bayt`
  - `scraper.tokyodev`
  - `scraper.japandev`
- **Dead Letter Queues**: Each queue has corresponding `_dlq` for failed messages

#### Production-Ready Features
- **Durable Queues**: Messages persist across server restarts
- **Message Persistence**: `DeliveryMode: amqp.Persistent`
- **Manual Acknowledgment**: Messages only removed after successful processing
- **Dead Letter Exchange**: Failed messages routed to DLX after max retries
- **Message TTL**: 24-hour expiration to prevent queue buildup
- **QoS Control**: Prefetch count of 1 for controlled message delivery
- **Retry Logic**: Up to 3 delivery attempts before DLX routing

### 4. Code Changes

#### Files Modified
1. **`api/main.go`**
   - Import: `infrastructure/nats` → `infrastructure/rabbitmq`
   - Client: `nats.NewNatsClient()` → `rabbitmq.NewRabbitMQClient()`
   - Variable: `nc` → `rmq`

2. **`api/app/app.go`**
   - Import: `infrastructure/nats` → `infrastructure/rabbitmq`
   - Parameter: `*nats.NatsClient` → `*rabbitmq.RabbitMQClient`
   - Variable: `nc` → `rmq`

3. **`api/commands/job/create-job.go`**
   - Import: `infrastructure/nats` → `infrastructure/rabbitmq`
   - Struct field: `nc *nats.NatsClient` → `rmq *rabbitmq.RabbitMQClient`
   - Method call: `nats.LinkedInSubTopic` → `rabbitmq.LinkedInQueue`

4. **`scraper/main.go`**
   - Import: `infrastructure/nats` → `infrastructure/rabbitmq`
   - Removed: `github.com/nats-io/nats.go` import
   - Client: `NewNatsClient()` → `NewRabbitMQClient()`
   - Subscribe method: Changed from NATS message handler to RabbitMQ message handler
   - Handler signature: `func(msg *nats.Msg)` → `func(data []byte) error`

5. **`inspect_nats.go` → `inspect_rabbitmq.go`**
   - Complete rewrite for RabbitMQ queue inspection
   - Features: Queue status, message counts, dead letter queue monitoring

6. **`Makefile`**
   - Target: `nats-server` → `rabbitmq-server`
   - Command: NATS Docker command → RabbitMQ Docker command

### 5. Handler Interface Changes

#### NATS Handler (Old)
```go
func(msg *nats.Msg) {
    // Process msg.Data
    msg.Ack() // or msg.Nak()
}
```

#### RabbitMQ Handler (New)
```go
func(data []byte) error {
    // Process data
    return nil // or return error for retry
}
```

### 6. Configuration Changes

#### Environment Variables
- **Added**: `RABBITMQ_URL=amqp://guest:guest@localhost:5672/`
- **Default**: Falls back to localhost if not set

#### Connection Settings
- **Retry Logic**: 5 connection attempts with 5-second delays
- **Auto-reconnect**: Built into RabbitMQ client
- **Channel Management**: Single channel per client instance

## Migration Benefits

### 1. Enhanced Reliability
- **Message Persistence**: Messages survive server restarts
- **Dead Letter Exchange**: Failed messages captured for analysis
- **Durable Queues**: Queue definitions persist across restarts
- **Manual Acknowledgment**: Prevents message loss

### 2. Better Monitoring
- **Management UI**: Web interface at http://localhost:15672
- **Queue Metrics**: Message counts, consumer counts, processing rates
- **Dead Letter Monitoring**: Track failed message patterns
- **Custom Inspection Tool**: `inspect_rabbitmq.go` for queue status

### 3. Production Readiness
- **Horizontal Scaling**: Multiple consumers per queue
- **Load Balancing**: Round-robin message distribution
- **Backpressure Control**: QoS prefetch limits
- **Message TTL**: Prevents infinite queue growth

### 4. Operational Improvements
- **Industry Standard**: RabbitMQ is widely adopted
- **Rich Ecosystem**: Extensive tooling and monitoring
- **Documentation**: Comprehensive official documentation
- **Community Support**: Large community and resources

## Testing Verification

✅ **Build Tests**: All components compile successfully
- `go build ./api/...` - ✅ Success
- `go build ./scraper` - ✅ Success  
- `go build ./inspect_rabbitmq.go` - ✅ Success

✅ **Dependency Management**: `go mod tidy` completed without errors

✅ **Import Resolution**: All RabbitMQ imports resolve correctly

## Usage Instructions

### 1. Start RabbitMQ
```bash
make rabbitmq-server
# OR
docker run --rm -p 5672:5672 -p 15672:15672 rabbitmq:3-management
```

### 2. Start API Server
```bash
cd api && go run main.go
```

### 3. Start Scraper Worker
```bash
cd scraper && go run main.go
```

### 4. Monitor Queues
```bash
go run inspect_rabbitmq.go
# OR visit http://localhost:15672 (guest/guest)
```

## Rollback Plan

If rollback is needed:
1. Revert `go.mod` changes
2. Restore `infrastructure/nats/` directory
3. Revert all import statements
4. Restore NATS-specific handler signatures
5. Run `go mod tidy`

## Next Steps

1. **Test with RabbitMQ**: Start RabbitMQ server and test message flow
2. **Monitor Performance**: Compare performance with previous NATS implementation
3. **Configure Production**: Set up RabbitMQ cluster for production deployment
4. **Update Documentation**: Ensure all documentation reflects RabbitMQ usage
5. **Team Training**: Brief team on RabbitMQ management and monitoring

## Migration Status: ✅ COMPLETE

The migration from NATS to RabbitMQ has been successfully completed. All code compiles, dependencies are resolved, and the system is ready for testing with RabbitMQ.