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Module 4: Relays & Network Architecture

Module Overview

Duration: 5-6 hours
Level: Intermediate
Prerequisites: Modules 1-3 completed
Goal: Master Nostr's relay architecture, network topology, and relay selection strategies

📋 Learning Objectives

By the end of this module, you will:

  • ✅ Understand relay architecture and protocols
  • ✅ Master WebSocket connections and message flow
  • ✅ Implement relay pool management
  • ✅ Configure relay selection strategies
  • ✅ Set up and run your own relay
  • ✅ Optimize network performance and reliability

4.1 Understanding Relays

What is a Relay?

A relay is a simple server that: - Accepts events from clients - Stores events (based on its policy) - Forwards events to interested clients - Filters events based on subscriptions

graph LR
    C1[Client 1] -->|Publish| R[Relay]
    C2[Client 2] -->|Subscribe| R
    R -->|Broadcast| C2
    C3[Client 3] -->|Subscribe| R
    R -->|Broadcast| C3

    style R fill:#9c27b0,stroke:#fff,color:#fff

Relay Responsibilities

Function Description Implementation
Accept Events Validate and store incoming events Check signatures, apply policies
Store Events Persist events to database PostgreSQL, MongoDB, SQLite
Query Events Retrieve based on filters Index by id, pubkey, kind, tags
Broadcast Send events to subscribers WebSocket connections
Apply Policies Enforce rules and limits Rate limiting, content filtering

Relay Types

  1. Public Relays
  2. Open to everyone
  3. Free or paid
  4. May have content policies

  5. Examples: relay.damus.io, nos.lol

  6. Private Relays

  7. Restricted access
  8. Whitelist/invite only
  9. Custom for communities

  10. Enhanced privacy

  11. Specialized Relays

  12. Long-form content
  13. Media storage
  14. Geographic specific

  15. Topic focused

  16. Personal Relays

  17. Run by individuals
  18. Complete control
  19. Backup storage
  20. Privacy focused

4.2 WebSocket Protocol

Connection Lifecycle

// Connecting to a relay
const relay = new WebSocket('wss://relay.example.com');

// Connection states
relay.onopen = () => {
  console.log('Connected to relay');
};

relay.onmessage = (event) => {
  const message = JSON.parse(event.data);
  handleRelayMessage(message);
};

relay.onerror = (error) => {
  console.error('Relay error:', error);
};

relay.onclose = () => {
  console.log('Disconnected from relay');
  // Implement reconnection logic
};

Message Types

Nostr uses three main message types between clients and relays:

1. CLIENT → RELAY Messages

EVENT - Publish an event: 

["EVENT", {event_object}]

REQ - Request/subscribe to events: 

["REQ", "subscription_id", {filter1}, {filter2}, ...]

CLOSE - Cancel subscription: 

["CLOSE", "subscription_id"]

2. RELAY → CLIENT Messages

EVENT - Send requested event: 

["EVENT", "subscription_id", {event_object}]

OK - Acknowledge event status: 

["OK", "event_id", true, "message"]

EOSE - End of stored events: 

["EOSE", "subscription_id"]

NOTICE - Relay message: 

["NOTICE", "message"]

AUTH - Authentication required: 

["AUTH", "challenge"]

Communication Flow

sequenceDiagram
    participant C as Client
    participant R as Relay

    C->>R: Connect WebSocket
    R->>C: Connected

    C->>R: ["REQ", "sub1", {filter}]
    R->>C: ["EVENT", "sub1", {event1}]
    R->>C: ["EVENT", "sub1", {event2}]
    R->>C: ["EOSE", "sub1"]

    C->>R: ["EVENT", {new_event}]
    R->>C: ["OK", "event_id", true, ""]

    R->>C: ["EVENT", "sub1", {new_event}]

    C->>R: ["CLOSE", "sub1"]
    C->>R: Disconnect

4.3 Relay Pool Management

Why Use Multiple Relays?

  1. Redundancy - If one relay is down
  2. Censorship Resistance - No single point of failure
  3. Geographic Distribution - Better latency
  4. Content Availability - Different relays have different events
  5. Load Balancing - Distribute traffic

Implementing a Relay Pool

class RelayPool {
  constructor() {
    this.relays = new Map();
    this.subscriptions = new Map();
  }

  addRelay(url, options = {}) {
    if (this.relays.has(url)) return;

    const relay = {
      url,
      ws: null,
      status: 'disconnected',
      stats: {
        eventsReceived: 0,
        eventsSent: 0,
        latency: null
      },
      options
    };

    this.connect(relay);
    this.relays.set(url, relay);
  }

  connect(relay) {
    relay.ws = new WebSocket(relay.url);

    relay.ws.onopen = () => {
      relay.status = 'connected';
      console.log(`Connected to ${relay.url}`);
      this.syncSubscriptions(relay);
    };

    relay.ws.onmessage = (event) => {
      relay.stats.eventsReceived++;
      this.handleMessage(relay, JSON.parse(event.data));
    };

    relay.ws.onerror = (error) => {
      console.error(`Error with ${relay.url}:`, error);
      this.reconnect(relay);
    };

    relay.ws.onclose = () => {
      relay.status = 'disconnected';
      this.reconnect(relay);
    };
  }

  publish(event) {
    const results = [];

    this.relays.forEach((relay) => {
      if (relay.status === 'connected') {
        relay.ws.send(JSON.stringify(['EVENT', event]));
        relay.stats.eventsSent++;
        results.push({ relay: relay.url, status: 'sent' });
      }
    });

    return results;
  }

  subscribe(filters, callback, id = null) {
    const subId = id || Math.random().toString(36).substring(7);

    this.subscriptions.set(subId, {
      filters,
      callback,
      events: new Set() // Deduplication
    });

    this.relays.forEach((relay) => {
      if (relay.status === 'connected') {
        relay.ws.send(JSON.stringify(['REQ', subId, ...filters]));
      }
    });

    return subId;
  }

  handleMessage(relay, message) {
    const [type, ...args] = message;

    switch (type) {
      case 'EVENT':
        const [subId, event] = args;
        const sub = this.subscriptions.get(subId);

        if (sub && !sub.events.has(event.id)) {
          sub.events.add(event.id);
          sub.callback(event, relay.url);
        }
        break;

      case 'EOSE':
        console.log(`End of stored events from ${relay.url}`);
        break;

      case 'OK':
        const [eventId, success, message] = args;
        console.log(`Event ${eventId}: ${success ? 'accepted' : 'rejected'} - ${message}`);
        break;

      case 'NOTICE':
        console.log(`Notice from ${relay.url}: ${args[0]}`);
        break;
    }
  }

  reconnect(relay, delay = 5000) {
    setTimeout(() => {
      console.log(`Reconnecting to ${relay.url}...`);
      this.connect(relay);
    }, delay);
  }
}

Relay Selection Strategies

1. Geographic Strategy

function selectRelaysByLocation(userLocation) {
  const relayLocations = {
    'wss://relay.damus.io': { lat: 37.7749, lon: -122.4194 }, // SF
    'wss://relay.nostr.band': { lat: 52.5200, lon: 13.4050 }, // Berlin
    'wss://relay.snort.social': { lat: 40.7128, lon: -74.0060 }, // NYC
  };

  return Object.entries(relayLocations)
    .map(([url, location]) => ({
      url,
      distance: calculateDistance(userLocation, location)
    }))
    .sort((a, b) => a.distance - b.distance)
    .slice(0, 3)
    .map(r => r.url);
}

2. Performance Strategy

class PerformanceRelaySelector {
  constructor() {
    this.metrics = new Map();
  }

  updateMetrics(relayUrl, latency, uptime, eventsPerSecond) {
    this.metrics.set(relayUrl, {
      latency,
      uptime,
      eventsPerSecond,
      score: this.calculateScore(latency, uptime, eventsPerSecond)
    });
  }

  calculateScore(latency, uptime, eventsPerSecond) {
    return (uptime * 100) + (eventsPerSecond * 10) - (latency * 0.1);
  }

  selectBestRelays(count = 5) {
    return Array.from(this.metrics.entries())
      .sort((a, b) => b[1].score - a[1].score)
      .slice(0, count)
      .map(([url]) => url);
  }
}

3. Content Strategy

function selectRelaysByContent(desiredEventKinds) {
  const relaySpecialties = {
    'wss://relay.damus.io': [0, 1, 3, 7], // General purpose
    'wss://relay.nostr.band': [1, 6, 7], // Social content
    'wss://nostr.wine': [0, 1, 30023], // Long-form
    'wss://purplepag.es': [0, 3], // Profiles
  };

  return Object.entries(relaySpecialties)
    .filter(([url, kinds]) => 
      desiredEventKinds.some(k => kinds.includes(k))
    )
    .map(([url]) => url);
}

4.4 Running Your Own Relay

Implementation Language Features Best For
nostr-rs-relay Rust Fast, efficient Production use
strfry C++ High performance Large scale
nostream TypeScript Feature-rich Customization
nostr-relay-nestjs TypeScript Modular Development
knostr Kotlin JVM ecosystem Java developers

Setting Up nostr-rs-relay

Step 1: Installation

# Using Docker
docker pull scsibug/nostr-rs-relay
docker run -p 7000:8080 scsibug/nostr-rs-relay

# From source
git clone https://github.com/scsibug/nostr-rs-relay.git
cd nostr-rs-relay
cargo build --release

Step 2: Configuration

# config.toml
[info]
relay_url = "wss://your-relay.com/"
name = "Your Relay Name"
description = "A Nostr relay"
pubkey = "your-hex-pubkey"
contact = "admin@your-relay.com"

[database]
engine = "sqlite"
data_directory = "./data"

[network]
port = 8080
address = "0.0.0.0"

[limits]
messages_per_sec = 10
max_event_bytes = 65536
max_ws_message_bytes = 131072
max_subscriptions = 20
max_filters = 100

[authorization]
pubkey_whitelist = []
pubkey_blacklist = []

[retention]
# Days to keep events
default = 30

Step 3: Nginx Reverse Proxy

server {
    listen 443 ssl http2;
    server_name relay.yoursite.com;

    ssl_certificate /path/to/cert.pem;
    ssl_certificate_key /path/to/key.pem;

    location / {
        proxy_pass http://localhost:8080;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_read_timeout 86400;
    }
}

Relay Policies

Content Filtering

// Example relay policy implementation
class RelayPolicy {
  constructor() {
    this.rules = [];
  }

  addRule(rule) {
    this.rules.push(rule);
  }

  async validateEvent(event) {
    for (const rule of this.rules) {
      const result = await rule.validate(event);
      if (!result.valid) {
        return {
          accepted: false,
          reason: result.reason
        };
      }
    }
    return { accepted: true };
  }
}

// Spam filter rule
class SpamFilterRule {
  constructor() {
    this.recentEvents = new Map();
  }

  async validate(event) {
    const key = event.pubkey;
    const now = Date.now();

    if (!this.recentEvents.has(key)) {
      this.recentEvents.set(key, []);
    }

    const recent = this.recentEvents.get(key)
      .filter(time => now - time < 60000); // Last minute

    if (recent.length > 10) {
      return {
        valid: false,
        reason: 'Rate limit exceeded'
      };
    }

    recent.push(now);
    this.recentEvents.set(key, recent);

    return { valid: true };
  }
}

4.5 Network Topology

Relay Discovery

NIP-65: Relay List Metadata

// Users publish their relay preferences
const relayListEvent = {
  kind: 10002,
  tags: [
    ["r", "wss://relay.damus.io", "read"],
    ["r", "wss://nos.lol", "write"],
    ["r", "wss://relay.nostr.band", "read"],
  ],
  content: ""
};

Gossip Model

class GossipRelayDiscovery {
  constructor(pool) {
    this.pool = pool;
    this.discoveredRelays = new Set();
    this.userRelayMap = new Map();
  }

  async discoverRelaysForUser(pubkey) {
    // Get user's relay list
    const filter = {
      authors: [pubkey],
      kinds: [10002],
      limit: 1
    };

    const relayList = await this.pool.queryOne(filter);

    if (relayList) {
      const relays = relayList.tags
        .filter(tag => tag[0] === 'r')
        .map(tag => ({
          url: tag[1],
          type: tag[2] || 'both'
        }));

      this.userRelayMap.set(pubkey, relays);
      relays.forEach(r => this.discoveredRelays.add(r.url));

      return relays;
    }

    return [];
  }

  async findUserAcrossRelays(pubkey) {
    // Query known relays for user
    const relays = this.userRelayMap.get(pubkey) || [];

    if (relays.length === 0) {
      // Try popular relays
      return this.tryPopularRelays(pubkey);
    }

    return relays.map(r => r.url);
  }
}

Relay Synchronization

class RelaySyncManager {
  constructor(primaryRelay, backupRelays) {
    this.primary = primaryRelay;
    this.backups = backupRelays;
    this.syncedEvents = new Set();
  }

  async syncUserData(pubkey) {
    // Get all user events from primary
    const events = await this.primary.query({
      authors: [pubkey]
    });

    // Sync to backups
    for (const backup of this.backups) {
      for (const event of events) {
        if (!this.syncedEvents.has(event.id)) {
          await backup.publish(event);
          this.syncedEvents.add(event.id);
        }
      }
    }

    return {
      eventsCount: events.length,
      syncedTo: this.backups.length
    };
  }

  async setupBidirectionalSync() {
    // Subscribe to new events on primary
    this.primary.subscribe(
      [{ since: Math.floor(Date.now() / 1000) }],
      (event) => {
        // Forward to backups
        this.backups.forEach(backup => {
          backup.publish(event);
        });
      }
    );

    // Subscribe to backups
    this.backups.forEach(backup => {
      backup.subscribe(
        [{ since: Math.floor(Date.now() / 1000) }],
        (event) => {
          // Forward to primary and other backups
          this.primary.publish(event);
          this.backups
            .filter(b => b !== backup)
            .forEach(b => b.publish(event));
        }
      );
    });
  }
}

4.6 Performance Optimization

Connection Management

class OptimizedRelayConnection {
  constructor(url) {
    this.url = url;
    this.ws = null;
    this.messageQueue = [];
    this.reconnectDelay = 1000;
    this.maxReconnectDelay = 30000;
    this.pingInterval = null;
  }

  connect() {
    this.ws = new WebSocket(this.url);

    this.ws.onopen = () => {
      this.reconnectDelay = 1000;
      this.flushQueue();
      this.startPing();
    };

    this.ws.onclose = () => {
      this.stopPing();
      this.reconnect();
    };
  }

  startPing() {
    this.pingInterval = setInterval(() => {
      if (this.ws.readyState === WebSocket.OPEN) {
        this.ws.send('ping');
      }
    }, 30000);
  }

  stopPing() {
    if (this.pingInterval) {
      clearInterval(this.pingInterval);
      this.pingInterval = null;
    }
  }

  send(message) {
    if (this.ws.readyState === WebSocket.OPEN) {
      this.ws.send(JSON.stringify(message));
    } else {
      this.messageQueue.push(message);
    }
  }

  flushQueue() {
    while (this.messageQueue.length > 0) {
      const message = this.messageQueue.shift();
      this.ws.send(JSON.stringify(message));
    }
  }

  reconnect() {
    setTimeout(() => {
      this.connect();
      this.reconnectDelay = Math.min(
        this.reconnectDelay * 2,
        this.maxReconnectDelay
      );
    }, this.reconnectDelay);
  }
}

Batch Processing

class BatchedRelayClient {
  constructor(relay) {
    this.relay = relay;
    this.eventBatch = [];
    this.batchSize = 10;
    this.batchTimeout = 100; // ms
    this.batchTimer = null;
  }

  publishEvent(event) {
    this.eventBatch.push(event);

    if (this.eventBatch.length >= this.batchSize) {
      this.flush();
    } else if (!this.batchTimer) {
      this.batchTimer = setTimeout(() => this.flush(), this.batchTimeout);
    }
  }

  flush() {
    if (this.batchTimer) {
      clearTimeout(this.batchTimer);
      this.batchTimer = null;
    }

    if (this.eventBatch.length === 0) return;

    const batch = this.eventBatch.splice(0);

    // Send all events efficiently
    batch.forEach(event => {
      this.relay.send(['EVENT', event]);
    });
  }
}

Caching Strategy

class CachedRelayClient {
  constructor() {
    this.eventCache = new Map();
    this.profileCache = new Map();
    this.cacheExpiry = 5 * 60 * 1000; // 5 minutes
  }

  async getEvent(eventId, relay) {
    // Check cache first
    const cached = this.eventCache.get(eventId);
    if (cached && Date.now() - cached.timestamp < this.cacheExpiry) {
      return cached.event;
    }

    // Fetch from relay
    const event = await relay.queryOne({ ids: [eventId] });

    if (event) {
      this.eventCache.set(eventId, {
        event,
        timestamp: Date.now()
      });
    }

    return event;
  }

  async getProfile(pubkey, relay) {
    const cached = this.profileCache.get(pubkey);
    if (cached && Date.now() - cached.timestamp < this.cacheExpiry) {
      return cached.profile;
    }

    const profileEvent = await relay.queryOne({
      authors: [pubkey],
      kinds: [0],
      limit: 1
    });

    if (profileEvent) {
      const profile = JSON.parse(profileEvent.content);
      this.profileCache.set(pubkey, {
        profile,
        timestamp: Date.now()
      });
      return profile;
    }

    return null;
  }

  pruneCache() {
    const now = Date.now();

    for (const [key, value] of this.eventCache.entries()) {
      if (now - value.timestamp > this.cacheExpiry) {
        this.eventCache.delete(key);
      }
    }

    for (const [key, value] of this.profileCache.entries()) {
      if (now - value.timestamp > this.cacheExpiry) {
        this.profileCache.delete(key);
      }
    }
  }
}

4.7 Practical Exercises

Exercise 1: Build a Relay Client

  1. Create a WebSocket connection to a relay
  2. Implement all message types (EVENT, REQ, CLOSE)
  3. Handle reconnection on disconnect
  4. Add proper error handling

Exercise 2: Implement Relay Pool

  1. Connect to 3 different relays
  2. Implement event deduplication
  3. Add relay health monitoring
  4. Test failover when a relay disconnects

Exercise 3: Set Up Your Own Relay

  1. Install nostr-rs-relay or strfry
  2. Configure with custom policies
  3. Set up SSL with Let's Encrypt
  4. Test with multiple clients

Exercise 4: Relay Discovery

  1. Implement NIP-65 relay list fetching
  2. Discover relays from user's contacts
  3. Build a relay recommendation system
  4. Test with real Nostr data

Exercise 5: Performance Testing

  1. Measure latency to different relays
  2. Test throughput with batch publishing
  3. Implement and measure caching effectiveness
  4. Create a relay benchmark tool

4.8 Troubleshooting Common Issues

Connection Problems

Issue Cause Solution
Connection drops Network instability Implement exponential backoff
Can't connect Firewall/SSL issues Check WebSocket support, certificates
Slow responses High latency Use geographic relay selection
Missing events Relay didn't store Query multiple relays

Performance Issues

// Diagnostic tool for relay performance
class RelayDiagnostics {
  async runDiagnostics(relayUrl) {
    const results = {
      connectivity: false,
      latency: null,
      throughput: null,
      eventSupport: {},
      errors: []
    };

    try {
      // Test connection
      const ws = new WebSocket(relayUrl);
      await new Promise((resolve, reject) => {
        ws.onopen = resolve;
        ws.onerror = reject;
        setTimeout(reject, 5000);
      });
      results.connectivity = true;

      // Test latency
      const start = Date.now();
      ws.send(JSON.stringify(['REQ', 'test', { limit: 1 }]));
      await new Promise(resolve => {
        ws.onmessage = resolve;
        setTimeout(resolve, 5000);
      });
      results.latency = Date.now() - start;

      ws.close();
    } catch (error) {
      results.errors.push(error.message);
    }

    return results;
  }
}

📝 Module 4 Quiz

  1. What are the three main message types clients send to relays?

    Answer EVENT (publish), REQ (subscribe/request), and CLOSE (end subscription)

  2. Why should you use multiple relays?

    Answer For redundancy, censorship resistance, geographic distribution, content availability, and load balancing

  3. What does EOSE mean and when is it sent?

    Answer "End Of Stored Events" - sent by relay after all stored events matching a subscription have been sent

  4. What is NIP-65 used for?

    Answer Relay List Metadata - allows users to publish their preferred relays for reading and writing

  5. What strategies can optimize relay performance?

    Answer Connection pooling, batch processing, caching, geographic selection, and implementing reconnection with exponential backoff

🎯 Module 4 Checkpoint

Before moving to Module 5, ensure you have:

  • [ ] Connected to multiple relays via WebSocket
  • [ ] Implemented a basic relay pool manager
  • [ ] Set up and configured your own relay
  • [ ] Handled all relay message types
  • [ ] Implemented relay discovery using NIP-65
  • [ ] Created performance monitoring for relays
  • [ ] Tested failover and redundancy
  • [ ] Optimized with caching and batching

📚 Additional Resources

💬 Community Discussion

Join our Discord to discuss Module 4: - Share your relay setup experiences - Get help with relay configuration - Discuss relay selection strategies - Compare relay performance metrics

Congratulations!

You've mastered Nostr's relay architecture! You understand WebSocket communication, can manage relay pools, run your own relay, and optimize network performance. You're ready to build robust Nostr applications!

Continue to Module 5: Building Your First Nostr Client →