Migration Guide (v1 to v2)

This guide helps you migrate from Agent Protocol v1 to v2. The v2 protocol offers significant improvements in performance, reliability, and observability while maintaining conceptual compatibility.

Why Migrate?

Improvement	v1	v2
Latency	~50μs per request	~10-20μs per request
Throughput	Single connection	Pooled connections (4x+ throughput)
Reliability	Basic timeouts	Circuit breakers, health tracking
Streaming	Limited	Full bidirectional streaming
Observability	Manual	Built-in Prometheus metrics
NAT Traversal	Not supported	Reverse connections

---

Quick Migration

Minimal Change (Drop-in)

If you just want pooling benefits without code changes:

Before (v1):

use sentinel_agent_protocol::AgentClient;

let client = AgentClient::unix_socket(
    "proxy",
    "/var/run/agent.sock",
    Duration::from_secs(5),
).await?;

let response = client.send_event(EventType::RequestHeaders, &event).await?;

After (v2):

use sentinel_agent_protocol::v2::AgentPool;

let pool = AgentPool::new();
pool.add_agent("agent", "/var/run/agent.sock").await?;

let response = pool.send_request_headers("agent", &headers).await?;

The AgentPool automatically:

• Maintains 4 connections per agent
• Load balances requests
• Tracks health and circuit breaker state
• Exports Prometheus metrics

---

Step-by-Step Migration

1. Update Dependencies

# Cargo.toml
[dependencies]
sentinel-agent-protocol = "0.3"  # v2 included

2. Import v2 Types

// Before
use sentinel_agent_protocol::{AgentClient, EventType, AgentEvent};

// After
use sentinel_agent_protocol::v2::{
    AgentPool,
    AgentPoolConfig,
    LoadBalanceStrategy,
    Decision,
};

3. Replace Client with Pool

Before:

// Create individual clients
let waf_client = AgentClient::unix_socket("proxy", "/run/waf.sock", timeout).await?;
let auth_client = AgentClient::grpc("http://localhost:50051", timeout).await?;

// Store clients somewhere
struct Clients {
    waf: AgentClient,
    auth: AgentClient,
}

After:

// Create single pool for all agents
let pool = AgentPool::new();

// Add agents (transport auto-detected)
pool.add_agent("waf", "/run/waf.sock").await?;
pool.add_agent("auth", "localhost:50051").await?;

// Pool is Clone + Send + Sync
let pool = Arc::new(pool);

4. Update Request Sending

Before:

let event = AgentEvent {
    event_type: EventType::RequestHeaders,
    request_id: req_id,
    method: method.to_string(),
    uri: uri.to_string(),
    headers: headers.clone(),
    // ...
};

let response = client.send_event(EventType::RequestHeaders, &event).await?;

After:

use sentinel_agent_protocol::v2::RequestHeadersEvent;

let event = RequestHeadersEvent {
    correlation_id: correlation_id.clone(),
    method: method.to_string(),
    uri: uri.to_string(),
    headers: headers.clone(),
    client_ip: client_ip.clone(),
    // ...
};

let response = pool.send_request_headers("waf", &event).await?;

5. Update Response Handling

Before:

match response.action {
    Action::Allow => { /* continue */ }
    Action::Block => {
        return Err(blocked_response(response.status_code));
    }
    Action::Redirect(url) => {
        return Ok(redirect_response(url));
    }
}

After:

match response.decision {
    Decision::Allow => { /* continue */ }
    Decision::Block { status, body, headers } => {
        return Err(blocked_response(status, body, headers));
    }
    Decision::Redirect { location, status } => {
        return Ok(redirect_response(location, status));
    }
    Decision::Modify { headers_to_add, headers_to_remove } => {
        apply_modifications(&mut request, headers_to_add, headers_to_remove);
    }
}

6. Add Error Handling for New Error Types

use sentinel_agent_protocol::v2::AgentProtocolError;

match pool.send_request_headers("waf", &event).await {
    Ok(response) => handle_response(response),

    // New in v2: Circuit breaker open
    Err(AgentProtocolError::CircuitBreakerOpen { agent_id }) => {
        tracing::warn!("Circuit open for {}, applying fallback", agent_id);
        apply_fallback_policy()
    }

    // New in v2: Flow control
    Err(AgentProtocolError::FlowControlPaused { agent_id }) => {
        tracing::warn!("Agent {} paused, request rejected", agent_id);
        apply_fallback_policy()
    }

    // Existing errors still work
    Err(AgentProtocolError::Timeout) => {
        apply_fallback_policy()
    }

    Err(e) => {
        tracing::error!("Agent error: {}", e);
        apply_fallback_policy()
    }
}

---

Configuration Migration

KDL Configuration

Before (v1):

agents {
    agent "waf" type="waf" {
        unix-socket "/var/run/waf.sock"
        timeout-ms 100
        failure-mode "open"
    }
}

After (v2):

agents {
    agent "waf" type="waf" {
        unix-socket "/var/run/waf.sock"
        protocol-version 2           // Enable v2
        connections 4                // Connection pool size
        timeout-ms 100
        failure-mode "open"

        // New v2 options
        circuit-breaker {
            failure-threshold 5
            reset-timeout-seconds 30
        }
    }
}

Rust Configuration

Before:

let client = AgentClient::unix_socket(
    "proxy",
    socket_path,
    Duration::from_millis(100),
).await?;

After:

let config = AgentPoolConfig {
    connections_per_agent: 4,
    load_balance_strategy: LoadBalanceStrategy::LeastConnections,
    request_timeout: Duration::from_millis(100),
    circuit_breaker_threshold: 5,
    circuit_breaker_reset_timeout: Duration::from_secs(30),
    ..Default::default()
};

let pool = AgentPool::with_config(config);
pool.add_agent("waf", socket_path).await?;

---

Feature-by-Feature Migration

Body Streaming

Before (v1):

// Send body as single event
let body_event = AgentEvent {
    event_type: EventType::RequestBody,
    body: Some(full_body),
    ..
};
client.send_event(EventType::RequestBody, &body_event).await?;

After (v2):

// Stream body in chunks
for (i, chunk) in body_chunks.enumerate() {
    let is_last = i == body_chunks.len() - 1;

    let chunk_event = RequestBodyChunkEvent {
        correlation_id: correlation_id.clone(),
        data: chunk,
        chunk_index: i as u32,
        is_last,
        ..Default::default()
    };

    pool.send_request_body_chunk("waf", &chunk_event).await?;
}

Health Checks

Before (v1):

// Manual health check
match client.ping().await {
    Ok(_) => { /* healthy */ }
    Err(_) => { /* unhealthy, handle manually */ }
}

After (v2):

// Automatic health tracking
let health = pool.get_health("waf")?;

println!("Healthy connections: {}/{}",
    health.healthy_connections,
    health.total_connections);
println!("Success rate: {:.1}%", health.success_rate * 100.0);
println!("Circuit breaker: {:?}", health.circuit_breaker_state);

Metrics

Before (v1):

// Manual metrics collection
metrics::counter!("agent_requests_total").increment(1);
let start = Instant::now();
let result = client.send_event(...).await;
metrics::histogram!("agent_request_duration").record(start.elapsed());

After (v2):

// Automatic metrics export
let prometheus_output = pool.metrics_collector().export_prometheus();
// Expose via /metrics endpoint

// Or get snapshot for custom handling
let snapshot = pool.protocol_metrics().snapshot();
println!("Total requests: {}", snapshot.requests_total);
println!("In-flight: {}", snapshot.in_flight_requests);

---

Agent-Side Migration

If you maintain custom agents, update the server implementation:

gRPC Agents

The protobuf definitions are compatible. Update to support new message types:

// New message types in v2
message RequestHeadersEvent {
    string correlation_id = 1;
    string method = 2;
    string uri = 3;
    map<string, StringList> headers = 4;
    // ...
}

message RequestBodyChunkEvent {
    string correlation_id = 1;
    bytes data = 2;
    bool is_last = 3;
    uint32 chunk_index = 4;
    // ...
}

UDS Agents

V2 UDS uses binary MessagePack encoding for better performance:

// Server handshake response includes encoding negotiation
let handshake = HandshakeResponse {
    agent_id: "my-agent".to_string(),
    supported_encodings: vec!["msgpack", "json"],
    capabilities: Capabilities {
        handles_request_body: true,
        handles_response_body: false,
        supports_streaming: true,
        max_concurrent_requests: Some(100),
    },
};

---

Rollback Plan

If you need to rollback to v1:

1. Keep v1 client code in a feature flag during migration
2. Monitor metrics during rollout
3. Gradual rollout using traffic splitting

#[cfg(feature = "agent-v2")]
async fn send_to_agent(event: &Event) -> Result<Response> {
    pool.send_request_headers("waf", event).await
}

#[cfg(not(feature = "agent-v2"))]
async fn send_to_agent(event: &Event) -> Result<Response> {
    client.send_event(EventType::RequestHeaders, event).await
}

---

Compatibility Notes

Wire Protocol

• v2 UDS uses length-prefixed MessagePack (or JSON with negotiation)
• v2 gRPC uses updated protobuf messages
• v1 agents cannot connect to v2 pool (and vice versa)

Breaking Changes

Change	Migration
AgentClient → AgentPool	Use pool pattern
send_event() → send_request_headers()	Update method calls
Action → Decision	Update response handling
EventType enum removed	Use typed methods
Request ID → Correlation ID	Use string correlation IDs

Deprecated (Still Working)

Deprecated	Replacement
AgentClient (v1)	AgentPool (v2)
JSON-only UDS	MessagePack UDS
Manual health checks	Automatic health tracking

---

Troubleshooting

“Connection refused” after migration

Ensure the agent supports v2 protocol. Check handshake:

# Test UDS connection
echo '{"type":"handshake","version":2}' | nc -U /var/run/agent.sock

Circuit breaker keeps opening

Tune thresholds for your error rates:

let config = AgentPoolConfig {
    circuit_breaker_threshold: 10,  // More tolerant
    circuit_breaker_reset_timeout: Duration::from_secs(10),  // Faster recovery
    ..Default::default()
};

Higher latency than expected

Check connection pool size and load balancing:

// For low-latency workloads
let config = AgentPoolConfig {
    connections_per_agent: 2,  // Fewer connections
    load_balance_strategy: LoadBalanceStrategy::LeastConnections,
    ..Default::default()
};

Memory usage increased

Large bodies may need mmap buffers:

[dependencies]
sentinel-agent-protocol = { version = "0.3", features = ["mmap-buffers"] }

---

Next Steps

After migration:

1. Enable metrics export - Add /metrics endpoint for Prometheus
2. Configure alerts - Set up alerts for circuit breaker state
3. Tune pool size - Adjust connections_per_agent based on load testing
4. Consider reverse connections - For agents behind NAT/firewalls

See also:

• API Reference
• Connection Pooling
• Transport Options