# Backend Logging Guide

## Overview

The E-Voting backend now includes comprehensive structured logging to help debug issues and understand the system's behavior.

## What's Logged

### Startup Sequence
```
🚀 Starting E-Voting Backend
📦 Initializing database...
✓ Database initialized successfully
⛓️  Initializing blockchain...
  ✓ Recorded election 1 (Election Présidentielle 2025)
    Block #0, Hash: 7f3e9c2b1d4f..., Candidates: 4
✓ Blockchain initialization completed
✓ Backend initialization complete, starting FastAPI app
```

### Blockchain Operations
```
Blockchain Initialization Started
Found 1 elections in database
Blockchain currently has 0 elections
  ✓ Recorded election 1 (Election Présidentielle 2025)
    Block #0, Hash: 7f3e9c2b..., Candidates: 4
Recording summary: 1 new, 0 skipped
Verifying blockchain integrity (1 blocks)...
✓ Blockchain integrity verified successfully
Blockchain Initialization Complete
  Total blocks: 1
  Chain valid: true
```

### Election Creation
```
✓ Election 1 recorded to blockchain (Block #0, Hash: 7f3e9c2b...)
```

### Errors and Warnings
```
❌ Failed to record election 1 to blockchain: [error details]
⚠️  Blockchain initialization failed (non-fatal): [error details]
🔥 Critical failure: [error details]
```

## Logging Levels

| Level | Emoji | Use Case |
|-------|-------|----------|
| DEBUG | 🔍 | Detailed diagnostic information, variable states |
| INFO | ℹ️ | General informational messages, success confirmations |
| WARNING | ⚠️ | Warning messages, potential issues (non-fatal) |
| ERROR | ❌ | Error messages, failures that need attention |
| CRITICAL | 🔥 | Critical failures that may prevent operation |

## Reading Log Output

### Example Log Entry
```
ℹ️  2025-11-07 02:03:15 - backend.init_blockchain - INFO - ✓ Recorded election 1 (Election Présidentielle 2025)
                       Block #0, Hash: 7f3e9c2b1d4f..., Candidates: 4
```

Parts:
- `ℹ️` - Log level emoji
- `2025-11-07 02:03:15` - Timestamp
- `backend.init_blockchain` - Module that logged it
- `INFO` - Log level
- Rest is the message

## Common Log Patterns

### Successful Blockchain Initialization
```
Blockchain Initialization Started
Found 1 elections in database
Blockchain currently has 0 elections
  ✓ Recorded election 1 (Election Présidentielle 2025)
    Block #0, Hash: 7f3e9c2b..., Candidates: 4
Recording summary: 1 new, 0 skipped
✓ Blockchain integrity verified successfully
Blockchain Initialization Complete
```
✓ **Status**: Backend is working correctly

### Election Already on Blockchain
```
  ⊘ Election 1 (Election Présidentielle 2025) already on blockchain
Recording summary: 0 new, 1 skipped
```
✓ **Status**: Restart is safe, election already recorded

### Database Connection Error
```
❌ Database initialization failed: [error details]
```
✗ **Status**: Database isn't accessible, check connection settings

### Blockchain Corruption Detected
```
✗ Blockchain integrity check FAILED - possible corruption!
```
✗ **Status**: Blockchain data is corrupted, investigate immediately

## Docker Logs

### View All Logs
```bash
docker compose -f docker-compose.multinode.yml logs -f
```

### View Backend Logs Only
```bash
docker compose -f docker-compose.multinode.yml logs -f backend-node-1
docker compose -f docker-compose.multinode.yml logs -f backend-node-2
docker compose -f docker-compose.multinode.yml logs -f backend-node-3
```

### View Database Logs
```bash
docker compose -f docker-compose.multinode.yml logs -f mariadb
```

### View Frontend Logs
```bash
docker compose -f docker-compose.multinode.yml logs -f frontend
```

### View Nginx Load Balancer Logs
```bash
docker compose -f docker-compose.multinode.yml logs -f nginx
```

## Debugging with Logs

### Problem: 502 Bad Gateway

**Check logs:**
```bash
docker compose logs backend-node-1 2>&1 | tail -100
```

**Look for:**
- `❌ Database initialization failed` - Database won't connect
- `⚠️  Blockchain initialization failed` - Blockchain error (non-fatal)
- `Exception` with full traceback - What specifically failed
- Module import errors - Missing or broken imports

### Problem: No Elections on Blockchain

**Check logs:**
```bash
docker compose logs backend-node-1 | grep -i blockchain
```

**Look for:**
- `Found X elections in database` - Are there elections?
- `✓ Recorded election` - Did recording succeed?
- `Recording summary` - How many were recorded vs skipped?
- `✓ Blockchain integrity verified` - Is blockchain valid?

### Problem: Slow Startup

**Check logs:**
```bash
docker compose logs backend-node-1 | grep -i "started\|initialized\|complete"
```

**Look for:**
- How long between "Starting" and "initialized successfully"
- Any pauses or long operations
- Database queries taking time

## Logging Configuration

**File:** `backend/logging_config.py`

Controls:
- Log levels per module
- Output format (colors, emojis, timestamps)
- Which third-party loggers to suppress (SQLAlchemy, Uvicorn, etc.)

### Modify Log Levels

To change log levels at runtime:

```python
# In backend code
import logging

# Get a logger
logger = logging.getLogger('backend.blockchain_elections')

# Change level
logger.setLevel(logging.DEBUG)  # More verbose
logger.setLevel(logging.WARNING)  # Less verbose
```

Or in `logging_config.py`:

```python
def setup_logging(level=logging.INFO):
    # Change specific module levels
    logging.getLogger('backend.blockchain_elections').setLevel(logging.DEBUG)
    logging.getLogger('backend.services').setLevel(logging.WARNING)
```

## Modules and Their Log Output

### `backend.main`
- Backend startup sequence
- Initialization status
- Fatal errors

### `backend.init_blockchain`
- Blockchain initialization
- Election recording
- Integrity verification
- Startup profiling

### `backend.services`
- Election creation
- Voter operations
- Vote recording
- Database operations

### `backend.routes`
- API endpoint calls
- Request/response info
- Validation errors

### `backend.database`
- Database connection
- Migration status
- Connection pooling info

## Performance Monitoring with Logs

### Track Blockchain Initialization Time

```bash
docker compose logs backend-node-1 | grep "Blockchain Initialization"
```

Output shows:
- When it started
- When it completed
- How many elections processed

Calculate total time: `start_time` to `complete_time`

### Track Election Recording Time

```bash
docker compose logs backend-node-1 | grep "Recorded election"
```

Each line shows:
- Election ID and name
- Block number assigned
- Hash of the block
- Candidate count

### Track Request Processing

```bash
docker compose logs backend-node-1 | grep "API\|request"
```

Shows which endpoints were called and when

## Exporting Logs

### Save to File
```bash
docker compose logs backend-node-1 > backend_logs.txt
```

### Search Logs for Pattern
```bash
docker compose logs | grep "❌\|✗"  # Errors and failures
docker compose logs | grep "✓"      # Successes
docker compose logs | grep "⚠️"      # Warnings
```

### Get Last N Lines
```bash
docker compose logs backend-node-1 --tail 50
```

### Get Logs Since Time
```bash
docker compose logs --since 2025-11-07T02:00:00
```

## Troubleshooting Checklist

When something goes wrong:

- [ ] Check backend logs for errors: `docker compose logs backend-node-1`
- [ ] Look for stack traces with `Exception` or `Error`
- [ ] Check database logs: `docker compose logs mariadb`
- [ ] Check if database initialized successfully
- [ ] Check if blockchain recorded elections
- [ ] Verify blockchain integrity status
- [ ] Check Nginx load balancer logs: `docker compose logs nginx`
- [ ] Verify all containers are healthy: `docker compose ps`

## Example Log Analysis

**Scenario**: Getting 502 errors but frontend loads

**Log search:**
```bash
docker compose logs backend-node-1 | head -100
```

**Expected healthy logs:**
```
🚀 Starting E-Voting Backend
📦 Initializing database...
✓ Database initialized successfully
⛓️  Initializing blockchain...
✓ Blockchain initialization completed
✓ Backend initialization complete, starting FastAPI app
```

**Red flags:**
```
❌ Database initialization failed     <- Backend can't connect to DB
⚠️  Blockchain initialization failed  <- Blockchain issue (non-fatal)
Exception in...                        <- Python error
Traceback...                           <- Stack trace
```

**Next steps:**
- If database failed: check MariaDB is running
- If blockchain failed: check elections table has data
- If exception: read the full traceback for details

## Real-Time Monitoring

### Watch Logs as Backend Starts
```bash
docker compose logs -f backend-node-1
```

Press Ctrl+C to stop. Useful for:
- Watching initialization progress
- Seeing exactly when things complete
- Catching errors as they happen

### Monitor Multiple Services
```bash
docker compose logs -f
```

Shows all logs from all services in real-time

## Questions the Logs Answer

| Question | Where to Look |
|----------|---------------|
| Why can't the backend connect to DB? | `backend.main` logs for `Database initialization failed` |
| Are elections being recorded to blockchain? | `backend.init_blockchain` logs for `Recorded election` |
| Is the blockchain valid? | `backend.init_blockchain` logs for `Blockchain integrity verified` |
| How long does startup take? | Timestamps between `Starting` and `complete` |
| What happened to my election creation? | `backend.services` logs for `Election recorded to blockchain` |
| Why are API requests failing? | `backend.routes` logs and `nginx` logs |
| Is the database healthy? | `mariadb` logs and connection messages in `backend.main` |

## Summary

The enhanced logging provides:
- ✓ Clear visibility into system state
- ✓ Colored output for easy scanning
- ✓ Emoji prefixes for quick identification
- ✓ Timestamp and module information
- ✓ Full exception details for debugging
- ✓ Separate concerns for different modules

Use the logs to:
1. Understand what's happening
2. Identify where failures occur
3. Debug issues quickly
4. Monitor system health
5. Track performance