TCP server protected from DDOS attacks with the Proof of Work

Features

• Proof of Work challenge using random quotes
• Configurable difficulty levels
• Rate limiting and connection limiting
• Worker pool for controlled concurrency
• Proper connection handling
• Timeouts to prevent hanging connections
• Nonce tracking with window expiration
• Graceful shutdown
• Comprehensive test coverage
• Docker support
• Prometheus metrics for monitoring

PoW Algorithm Choice:

• Using SHA256 with a nonce-based challenge
• The server generates a random quote and a target (currently set to 2)
• The client must find a nonce that, when combined with the quote and timestamp, produces a hash starting with the target
• This is computationally intensive but verifiable quickly
• The difficulty can be adjusted by changing the number of zeros in the target

Project Structure

.
├── cmd/                               # Main application entry points
│   ├── client/                        # Client application
│   └── server/                        # Server application
├── internal/                          # Private application code
│   ├── client/                        # Client implementation
│   └── server/                        # Server implementation
│       ├── service/                   # Server services
│       │   ├── connection_manager.go  # Connection handling and timeouts
│       │   ├── pow_service.go         # Proof of Work service
│       │   └── quote_service.go       # Quote service
│       └── handler.go                 # Main server handler
├── pkg/                               # Public libraries
│   ├── backoff/                       # Backoff queue implementation
│   ├── config/                        # Configuration handling
│   ├── connlimit/                     # Connection limiting
│   ├── metrics/                       # Prometheus metrics
│   ├── nonce/                         # Nonce tracking
│   ├── pow/                           # Proof of Work implementation
│   ├── quotes/                        # Quotes storage and retrieval
│   ├── ratelimit/                     # Rate limiting
│   └── workerpool/                    # Worker pool implementation
├── config/                            # Configuration files
├── vendor/                            # Dependencies
├── docker-compose.yml                 # Docker Compose configuration
├── client.Dockerfile                  # Client Dockerfile
└── server.Dockerfile                  # Server Dockerfile

Metrics

The server exposes the following Prometheus metrics:

Connection Metrics

• server_active_connections - Number of active connections
• server_total_connections - Total number of connections

PoW Metrics

• server_pow_challenges_generated - Number of PoW challenges generated
• server_pow_challenges_verified - Number of PoW challenges verified
• server_pow_verification_failures - Number of PoW verification failures

Rate Limiting Metrics

• server_rate_limit_hits - Number of rate limit hits

Worker Pool Metrics

• server_worker_pool_size - Current size of the worker pool
• server_worker_pool_queue_size - Current size of the worker pool queue

Response Time Metrics

• server_response_time_seconds - Response time in seconds (histogram)

How to RUN

git clone https://github.com/clevertechru/server_pow.git
cd server_pow
docker compose up --build

How to Run tests and linter

go test ./...
golangci-lint run ./...

Server environment settings

# Adjust difficulty by changing number of zeros
CHALLENGE_DIFFICULTY=2

# default server host and port
HOST=0.0.0.0
PORT=8080

# quotes configuration file path
QUOTES_CONFIG_PATH=/path/to/quotes.yml

Client environment settings

#default pow server host and port
SERVER_HOST=server
SERVER_PORT=8080

# default delay of requests
REQUESTS_DELAY_MS=100

Quotes Configuration

The server uses a YAML file to store quotes. Example format:

quotes:
  - "Quote 1"
  - "Quote 2"
  - "Quote 3"

Development

• Go 1.24 or later required
• Docker and Docker Compose for containerized deployment
• golangci-lint for code quality checks