# KVS - Distributed Key-Value Store

A minimalistic, clustered key-value database system written in Go that prioritizes **availability** and **partition tolerance** over strong consistency. KVS implements a gossip-style membership protocol with sophisticated conflict resolution for eventually consistent distributed storage.

## 🚀 Key Features

- **Hierarchical Keys**: Support for structured paths (e.g., `/home/room/closet/socks`)
- **Eventual Consistency**: Local operations are fast, replication happens in background
- **Merkle Tree Sync**: Efficient data synchronization with cryptographic integrity
- **Sophisticated Conflict Resolution**: Oldest-node rule with UUID tie-breaking
- **JWT Authentication**: Full authentication system with POSIX-inspired permissions
- **Local-First Truth**: All operations work locally first, sync globally later
- **Read-Only Mode**: Configurable mode for reducing write load
- **Modular Architecture**: Clean separation of concerns with feature toggles
- **Comprehensive Features**: TTL support, rate limiting, tamper logging, automated backups
- **Zero External Dependencies**: Single binary with embedded BadgerDB storage

## 🏗️ Architecture

```
┌─────────────────┐    ┌─────────────────┐    ┌─────────────────┐
│     Node A      │    │     Node B      │    │     Node C      │
│  (Go Service)   │    │  (Go Service)   │    │  (Go Service)   │
│                 │    │                 │    │                 │
│ ┌─────────────┐ │    │ ┌─────────────┐ │    │ ┌─────────────┐ │
│ │HTTP API+Auth│ │◄──►│ │HTTP API+Auth│ │◄──►│ │HTTP API+Auth│ │
│ └─────────────┘ │    │ └─────────────┘ │    │ └─────────────┘ │
│ ┌─────────────┐ │    │ ┌─────────────┐ │    │ ┌─────────────┐ │
│ │   Gossip    │ │◄──►│ │   Gossip    │ │◄──►│ │   Gossip    │ │
│ │  Protocol   │ │    │ │  Protocol   │ │    │ │  Protocol   │ │
│ └─────────────┘ │    │ └─────────────┘ │    │ └─────────────┘ │
│ ┌─────────────┐ │    │ ┌─────────────┐ │    │ ┌─────────────┐ │
│ │Merkle Sync  │ │◄──►│ │Merkle Sync  │ │◄──►│ │Merkle Sync  │ │
│ │& Conflict   │ │    │ │& Conflict   │ │    │ │& Conflict   │ │
│ │ Resolution  │ │    │ │ Resolution  │ │    │ │ Resolution  │ │
│ └─────────────┘ │    │ └─────────────┘ │    │ └─────────────┘ │
│ ┌─────────────┐ │    │ ┌─────────────┐ │    │ ┌─────────────┐ │
│ │Storage+     │ │    │ │Storage+     │ │    │ │Storage+     │ │
│ │Features     │ │    │ │Features     │ │    │ │Features     │ │
│ │(BadgerDB)   │ │    │ │(BadgerDB)   │ │    │ │(BadgerDB)   │ │
│ └─────────────┘ │    │ └─────────────┘ │    │ └─────────────┘ │
└─────────────────┘    └─────────────────┘    └─────────────────┘
        ▲
        │
External Clients (JWT Auth)
```

### Modular Design
KVS features a clean modular architecture with dedicated packages:
- **`auth/`** - JWT authentication and POSIX-inspired permissions
- **`cluster/`** - Gossip protocol, Merkle tree sync, and conflict resolution
- **`storage/`** - BadgerDB abstraction with compression and revisions
- **`server/`** - HTTP API, routing, and lifecycle management
- **`features/`** - TTL, rate limiting, tamper logging, backup utilities
- **`config/`** - Configuration management with auto-generation

## 📦 Installation

### Prerequisites
- Go 1.21 or higher

### Build from Source
```bash
git clone <repository-url>
cd kvs
go mod tidy
go build -o kvs .
```

### Quick Test
```bash
# Start standalone node (uses config.yaml if it exists, or creates it)
./kvs start config.yaml

# Test the API
curl http://localhost:8080/health

# Check status
./kvs status

# Stop when done
./kvs stop config
```

## 🎮 Process Management

KVS includes systemd-style daemon commands for easy process management:

```bash
# Start as background daemon
./kvs start config.yaml      # or just: ./kvs start config
./kvs start node1.yaml       # Start with custom config

# Check status
./kvs status                 # Show all running instances
./kvs status node1           # Show specific instance

# Stop daemon
./kvs stop node1             # Graceful shutdown

# Restart daemon
./kvs restart node1          # Stop and start

# Run in foreground (traditional)
./kvs node1.yaml             # Logs to stdout
```

### Daemon Features
- **Global PID tracking**: PID files stored in `~/.kvs/pids/` (works from any directory)
- **Automatic logging**: Logs written to `~/.kvs/logs/{config-name}.log`
- **Flexible naming**: Config extension optional (`node1` or `node1.yaml` both work)
- **Graceful shutdown**: SIGTERM sent for clean shutdown
- **Stale PID cleanup**: Automatically detects and cleans dead processes
- **Multi-instance**: Run multiple KVS instances on same machine

### Example Workflow
```bash
# Start 3-node cluster as daemons
./kvs start node1.yaml
./kvs start node2.yaml
./kvs start node3.yaml

# Check cluster status
./kvs status

# View logs
tail -f ~/.kvs/logs/kvs_node1.yaml.log

# Stop entire cluster
./kvs stop node1
./kvs stop node2
./kvs stop node3
```

## ⚙️ Configuration

KVS uses YAML configuration files. On first run, a default `config.yaml` is automatically generated:

```yaml
node_id: "hostname"                    # Unique node identifier
bind_address: "127.0.0.1"              # IP address to bind to
port: 8080                             # HTTP port
data_dir: "./data"                     # Directory for BadgerDB storage
seed_nodes: []                         # List of seed nodes for cluster joining
read_only: false                       # Enable read-only mode
log_level: "info"                      # Logging level (debug, info, warn, error)

# Cluster timing configuration
gossip_interval_min: 60                # Min gossip interval (seconds)
gossip_interval_max: 120               # Max gossip interval (seconds)
sync_interval: 300                     # Regular sync interval (seconds)
catchup_interval: 120                  # Catch-up sync interval (seconds)
bootstrap_max_age_hours: 720           # Max age for bootstrap sync (hours)
throttle_delay_ms: 100                 # Delay between sync requests (ms)
fetch_delay_ms: 50                     # Delay between data fetches (ms)

# Feature configuration
compression_enabled: true              # Enable ZSTD compression
compression_level: 3                   # Compression level (1-19)
default_ttl: "0"                       # Default TTL ("0" = no expiry)
max_json_size: 1048576                 # Max JSON payload size (1MB)
rate_limit_requests: 100               # Requests per window
rate_limit_window: "1m"                # Rate limit window

# Feature toggles
auth_enabled: true                     # JWT authentication system
tamper_logging_enabled: true           # Cryptographic audit trail
clustering_enabled: true               # Gossip protocol and sync
rate_limiting_enabled: true            # Rate limiting
revision_history_enabled: true         # Automatic versioning

# Anonymous access control (when auth_enabled: true)
allow_anonymous_read: false            # Allow unauthenticated read access to KV endpoints
allow_anonymous_write: false           # Allow unauthenticated write access to KV endpoints

# Backup configuration
backup_enabled: true                   # Automated backups
backup_schedule: "0 0 * * *"           # Daily at midnight (cron format)
backup_path: "./backups"               # Backup directory
backup_retention: 7                    # Days to keep backups
```

### Custom Configuration
```bash
# Use custom config file
./kvs /path/to/custom-config.yaml
```

## 🔌 REST API

### Data Operations (`/kv/`)

#### Store Data
```bash
PUT /kv/{path}
Content-Type: application/json
Authorization: Bearer <jwt-token>  # Required if auth_enabled && !allow_anonymous_write

# Basic storage
curl -X PUT http://localhost:8080/kv/users/john/profile \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer eyJ..." \
  -d '{"name":"John Doe","age":30,"email":"john@example.com"}'

# Storage with TTL
curl -X PUT http://localhost:8080/kv/cache/session/abc123 \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer eyJ..." \
  -d '{"data":{"user_id":"john"}, "ttl":"1h"}'

# Response
{
  "uuid": "a1b2c3d4-e5f6-7890-1234-567890abcdef",
  "timestamp": 1672531200000
}
```

#### Retrieve Data
```bash
GET /kv/{path}
Authorization: Bearer <jwt-token>  # Required if auth_enabled && !allow_anonymous_read

curl -H "Authorization: Bearer eyJ..." http://localhost:8080/kv/users/john/profile

# Response (full StoredValue format)
{
  "uuid": "a1b2c3d4-e5f6-7890-1234-567890abcdef",
  "timestamp": 1672531200000,
  "data": {
    "name": "John Doe",
    "age": 30,
    "email": "john@example.com"
  }
}
```

#### Delete Data
```bash
DELETE /kv/{path}
Authorization: Bearer <jwt-token>  # Always required when auth_enabled (no anonymous delete)

curl -X DELETE -H "Authorization: Bearer eyJ..." http://localhost:8080/kv/users/john/profile
# Returns: 204 No Content
```

### Authentication Operations (`/auth/`)

#### Create User
```bash
POST /auth/users
Content-Type: application/json

curl -X POST http://localhost:8080/auth/users \
  -H "Content-Type: application/json" \
  -d '{"nickname":"john"}'

# Response
{"uuid": "user-abc123"}
```

#### Create API Token
```bash
POST /auth/tokens
Content-Type: application/json

curl -X POST http://localhost:8080/auth/tokens \
  -H "Content-Type: application/json" \
  -d '{"user_uuid":"user-abc123", "scopes":["read","write"]}'

# Response
{
  "token": "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...",
  "expires_at": 1672617600000
}
```

### Cluster Operations (`/members/`)

#### View Cluster Members
```bash
GET /members/

curl http://localhost:8080/members/
# Response
[
  {
    "id": "node-alpha",
    "address": "192.168.1.10:8080",
    "last_seen": 1672531200000,
    "joined_timestamp": 1672530000000
  }
]
```

#### Health Check
```bash
GET /health

curl http://localhost:8080/health
# Response
{
  "status": "ok",
  "mode": "normal",
  "member_count": 2,
  "node_id": "node-alpha"
}
```

### Merkle Tree Operations (`/sync/`)

#### Get Merkle Root
```bash
GET /sync/merkle/root
# Used internally for data synchronization
```

#### Range Queries
```bash
GET /kv/_range?start_key=users/&end_key=users/z&limit=100
# Fetch key ranges for synchronization
```

## 🏘️ Cluster Setup

### Single Node (Standalone)
```bash
# config.yaml
node_id: "standalone"
port: 8080
seed_nodes: []  # Empty = standalone mode
```

### Multi-Node Cluster

#### Node 1 (Bootstrap Node)
```bash
# node1.yaml
node_id: "node1"
port: 8081
seed_nodes: []  # First node, no seeds needed
auth_enabled: true
clustering_enabled: true
```

#### Node 2 (Joins via Node 1)
```bash
# node2.yaml  
node_id: "node2"
port: 8082
seed_nodes: ["127.0.0.1:8081"]  # Points to node1
auth_enabled: true
clustering_enabled: true
```

#### Node 3 (Joins via Node 1 & 2)
```bash
# node3.yaml
node_id: "node3" 
port: 8083
seed_nodes: ["127.0.0.1:8081", "127.0.0.1:8082"]  # Multiple seeds for reliability
auth_enabled: true
clustering_enabled: true
```

#### Start the Cluster
```bash
# Start as daemons
./kvs start node1.yaml
sleep 2
./kvs start node2.yaml
sleep 2
./kvs start node3.yaml

# Verify cluster formation
curl http://localhost:8081/members/  # Should show all 3 nodes

# Check daemon status
./kvs status

# Stop cluster when done
./kvs stop node1
./kvs stop node2
./kvs stop node3
```

## 🔄 How It Works

### Gossip Protocol
- Nodes randomly select 1-3 peers every 1-2 minutes for membership exchange
- Failed nodes are detected via timeout (5 minutes) and removed (10 minutes)
- New members are automatically discovered and added to local member lists

### Merkle Tree Synchronization
- **Merkle Trees**: Each node builds cryptographic trees of their data for efficient comparison
- **Regular Sync**: Every 5 minutes, nodes compare Merkle roots and sync divergent branches
- **Catch-up Sync**: Every 2 minutes when nodes detect they're significantly behind
- **Bootstrap Sync**: New nodes gradually fetch historical data up to 30 days old
- **Efficient Detection**: Only synchronizes actual differences, not entire datasets

### Sophisticated Conflict Resolution
When two nodes have different data for the same key with identical timestamps:

1. **Detection**: Merkle tree comparison identifies conflicting keys
2. **Oldest-Node Rule**: The version from the node with earliest `joined_timestamp` wins
3. **UUID Tie-Breaker**: If join times are identical, lexicographically smaller UUID wins
4. **Automatic Resolution**: Losing nodes automatically fetch and store the winning version
5. **Consistency**: All nodes converge to the same data within seconds

### Authentication & Authorization
- **JWT Tokens**: Secure API access with scoped permissions
- **POSIX-Inspired ACLs**: 12-bit permission system (owner/group/others with create/delete/write/read)
- **Resource Metadata**: Each stored item has ownership and permission information
- **Feature Toggle**: Can be completely disabled for simpler deployments

### Operational Modes
- **Normal**: Full read/write capabilities with all features
- **Read-Only**: Rejects external writes but accepts internal replication
- **Syncing**: Temporary mode during bootstrap, rejects external writes

## 🛠️ Development

### Running Tests
```bash
# Build and run comprehensive integration tests
go build -o kvs .
./integration_test.sh

# Manual basic functionality test
./kvs start config.yaml
sleep 2
curl http://localhost:8080/health
./kvs stop config

# Manual cluster test (requires creating configs)
echo 'node_id: "test1"
port: 8081
seed_nodes: []
auth_enabled: false' > test1.yaml

echo 'node_id: "test2"
port: 8082
seed_nodes: ["127.0.0.1:8081"]
auth_enabled: false' > test2.yaml

./kvs start test1.yaml
sleep 2
./kvs start test2.yaml

# Test data replication (wait for cluster formation)
sleep 10
curl -X PUT http://localhost:8081/kv/test/data \
  -H "Content-Type: application/json" \
  -d '{"message":"hello world"}'

# Wait for Merkle sync, then check replication
sleep 30
curl http://localhost:8082/kv/test/data

# Cleanup
./kvs stop test1
./kvs stop test2
rm test1.yaml test2.yaml
```

### Conflict Resolution Testing
```bash
# Create conflicting data scenario using utility
go run test_conflict.go /tmp/conflict1 /tmp/conflict2

# Create configs for conflict test
echo 'node_id: "conflict1"
port: 9111
data_dir: "/tmp/conflict1"
seed_nodes: []
auth_enabled: false
log_level: "debug"' > conflict1.yaml

echo 'node_id: "conflict2"
port: 9112
data_dir: "/tmp/conflict2"
seed_nodes: ["127.0.0.1:9111"]
auth_enabled: false
log_level: "debug"' > conflict2.yaml

# Start nodes with conflicting data
./kvs start conflict1.yaml
sleep 2
./kvs start conflict2.yaml

# Watch logs for conflict resolution
tail -f ~/.kvs/logs/kvs_conflict1.yaml.log ~/.kvs/logs/kvs_conflict2.yaml.log &

# Both nodes will converge within ~10-30 seconds
# Check final state
sleep 30
curl http://localhost:9111/kv/test/conflict/data
curl http://localhost:9112/kv/test/conflict/data

# Cleanup
./kvs stop conflict1
./kvs stop conflict2
rm conflict1.yaml conflict2.yaml
```

### Code Quality
```bash
# Format and lint
go fmt ./...
go vet ./...

# Dependency management
go mod tidy
go mod verify

# Build verification
go build .
```

### Project Structure
```
kvs/
├── main.go                    # Main application entry point
├── config.yaml                # Default configuration (auto-generated)
├── integration_test.sh        # Comprehensive test suite
├── test_conflict.go           # Conflict resolution testing utility
├── CLAUDE.md                  # Development guidance for Claude Code
├── go.mod                     # Go module dependencies
├── go.sum                     # Go module checksums
├── README.md                  # This documentation
│
├── auth/                      # Authentication & authorization
│   ├── auth.go               # Main auth logic
│   ├── jwt.go                # JWT token management
│   ├── middleware.go         # HTTP middleware
│   ├── permissions.go        # POSIX-inspired ACL system
│   └── storage.go            # Auth data storage
│
├── cluster/                   # Distributed systems components
│   ├── bootstrap.go          # New node integration
│   ├── gossip.go             # Membership protocol
│   ├── merkle.go             # Merkle tree implementation
│   └── sync.go               # Data synchronization & conflict resolution
│
├── config/                    # Configuration management
│   └── config.go             # Config loading & defaults
│
├── daemon/                    # Process management
│   ├── daemonize.go          # Background process spawning
│   └── pid.go                # PID file management
│
├── features/                  # Utility features
│   ├── auth.go               # Auth utilities
│   ├── backup.go             # Backup system
│   ├── features.go           # Feature toggles
│   ├── ratelimit.go          # Rate limiting
│   ├── revision.go           # Revision history
│   ├── tamperlog.go          # Tamper-evident logging
│   └── validation.go         # TTL parsing
│
├── server/                    # HTTP server & API
│   ├── handlers.go           # Request handlers
│   ├── lifecycle.go          # Server lifecycle
│   ├── routes.go             # Route definitions
│   └── server.go             # Server setup
│
├── storage/                   # Data storage abstraction
│   ├── compression.go        # ZSTD compression
│   ├── revision.go           # Revision history
│   └── storage.go            # BadgerDB interface
│
├── types/                     # Shared type definitions
│   └── types.go              # All data structures
│
└── utils/                     # Utilities
    └── hash.go               # Cryptographic hashing
```

### Key Data Structures

#### Stored Value Format
```go
type StoredValue struct {
    UUID      string          `json:"uuid"`      // Unique version identifier
    Timestamp int64           `json:"timestamp"` // Unix timestamp (milliseconds)
    Data      json.RawMessage `json:"data"`      // Actual user JSON payload
}
```

#### BadgerDB Storage
- **Main Key**: Direct path mapping (e.g., `users/john/profile`)
- **Index Key**: `_ts:{timestamp}:{path}` for efficient time-based queries
- **Values**: JSON-marshaled `StoredValue` structures

## 🔧 Configuration Options Explained

| Setting | Description | Default | Notes |
|---------|-------------|---------|-------|
| **Core Settings** |
| `node_id` | Unique identifier for this node | hostname | Must be unique across cluster |
| `bind_address` | IP address to bind HTTP server | "127.0.0.1" | Use 0.0.0.0 for external access |
| `port` | HTTP port for API and cluster communication | 8080 | Must be accessible to peers |
| `data_dir` | Directory for BadgerDB storage | "./data" | Will be created if doesn't exist |
| `seed_nodes` | List of initial cluster nodes | [] | Empty = standalone mode |
| `read_only` | Enable read-only mode | false | Accepts replication, rejects client writes |
| `log_level` | Logging verbosity | "info" | debug/info/warn/error |
| **Cluster Timing** |
| `gossip_interval_min/max` | Gossip frequency range | 60-120 sec | Randomized interval |
| `sync_interval` | Regular Merkle sync frequency | 300 sec | How often to sync with peers |
| `catchup_interval` | Catch-up sync frequency | 120 sec | Faster sync when behind |
| `bootstrap_max_age_hours` | Max historical data to sync | 720 hours | 30 days default |
| **Feature Toggles** |
| `auth_enabled` | JWT authentication system | true | Complete auth/authz system |
| `allow_anonymous_read` | Allow unauthenticated read access | false | When auth_enabled, controls KV GET endpoints |
| `allow_anonymous_write` | Allow unauthenticated write access | false | When auth_enabled, controls KV PUT endpoints |
| `clustering_enabled` | Gossip protocol and sync | true | Distributed mode |
| `compression_enabled` | ZSTD compression | true | Reduces storage size |
| `rate_limiting_enabled` | Rate limiting | true | Per-client limits |
| `tamper_logging_enabled` | Cryptographic audit trail | true | Security logging |
| `revision_history_enabled` | Automatic versioning | true | Data history tracking |
| `catchup_interval` | Catch-up sync frequency | 120 sec | Faster sync when behind |
| `bootstrap_max_age_hours` | Max historical data to sync | 720 hours | 30 days default |
| `throttle_delay_ms` | Delay between sync requests | 100 ms | Prevents overwhelming peers |
| `fetch_delay_ms` | Delay between individual fetches | 50 ms | Rate limiting |

## 🚨 Important Notes

### Consistency Model
- **Eventual Consistency**: Data will eventually be consistent across all nodes
- **Local-First**: All operations succeed locally first, then replicate
- **No Transactions**: Each key operation is independent
- **Conflict Resolution**: Automatic resolution of timestamp collisions

### Network Requirements  
- All nodes must be able to reach each other via HTTP
- Firewalls must allow traffic on configured ports
- IPv4 private networks supported (IPv6 not tested)

### Limitations
- No encryption in transit (use reverse proxy for TLS)
- No cross-key transactions or ACID guarantees
- No complex queries (key-based lookups only)
- No automatic data sharding (single keyspace per cluster)
- No multi-datacenter replication

### Performance Characteristics
- **Read Latency**: ~1ms (local BadgerDB lookup)
- **Write Latency**: ~5ms (local write + indexing + optional compression)
- **Replication Lag**: 10-30 seconds with Merkle tree sync
- **Memory Usage**: Minimal (BadgerDB + Merkle tree caching)
- **Disk Usage**: Raw JSON + metadata + optional compression (10-50% savings)
- **Conflict Resolution**: Sub-second convergence time
- **Cluster Formation**: ~10-20 seconds for gossip stabilization

## 🛡️ Production Considerations

### Deployment
- Built-in daemon commands (`start`/`stop`/`restart`/`status`) for process management
- Alternatively, use systemd or similar for advanced orchestration
- Logs automatically written to `~/.kvs/logs/` (configure log rotation)
- Set up monitoring for `/health` endpoint
- Use reverse proxy (nginx/traefik) for TLS and load balancing

### Monitoring
- Monitor `/health` endpoint for node status
- Watch logs for conflict resolution events
- Track member count for cluster health
- Monitor disk usage in data directories

### Backup Strategy
- BadgerDB supports snapshots
- Data directories can be backed up while running
- Consider backing up multiple nodes for redundancy

### Scaling
- Add new nodes by configuring existing cluster members as seeds
- Remove nodes gracefully using `/members/leave` endpoint  
- Cluster can operate with any number of nodes (tested with 2-10)

## 📄 License

This project is licensed under the MIT License - see the LICENSE file for details.

## 🤝 Contributing

1. Fork the repository
2. Create a feature branch (`git checkout -b feature/amazing-feature`)
3. Commit your changes (`git commit -m 'Add amazing feature'`)
4. Push to the branch (`git push origin feature/amazing-feature`)
5. Open a Pull Request

## 📚 Additional Resources

- [BadgerDB Documentation](https://dgraph.io/docs/badger/)
- [Gossip Protocol Paper](https://www.cs.cornell.edu/home/rvr/papers/flowgossip.pdf)
- [Eventually Consistent Systems](https://www.allthingsdistributed.com/2008/12/eventually_consistent.html)

---

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