should be good to extend functionality now

README.md

@@ -5,6 +5,22 @@ Production't graden't load balancer.
 
 ## Todo
 - [ ] architecture astronauting
+  - balancer module
+    - just the algorithms i guess
+- 
+  - backend module
+    - manages the backend pool
+    - deals with health / load check
+    - BackendPool for all the backends stored together
+    - Backend for individual backends
+    - has some methods used by balancer module to pick a suitable backend
+  - proxy module 
+    - all the different supported protocols to handle
+    - will create a session / stream context structure (ConnectionContext)
+      - not globally tracked (this might change for UDP!)
+      - mainly some metadata
+  - config module
+    - set up all the stuff or something
 - [ ] stream / session handling (i think wrapper around tokio TcpStream)
 - [ ] basic backend pooling
 - [ ] layer 4 load balancing
@@ -103,3 +119,10 @@ process to load balance:
 - connect to the server
 - proxy the data (copy_bidirectional? maybe we want some metrics or logging, so might do manually)
 - cleanup when smoeone leavesr or something goes wrong (with TCP, OS / tokio will tell us, with UDP probably just timeout based, and a periodic sweep of all sessions)
+
+
+### UDP
+UDP is connectionless, and i don't think UdpSocket or UdpFramed implement the traits required for tokio copy_bidirectional
+but async write and read don't work on just regular datagrams, so probably not possible.
+
+Would require us to implement our own bidirectional copying / proxying, as well as tracking "active" connections.

src/backend/mod.rs

@@ -0,0 +1,58 @@
+use core::fmt;
+use std::net::SocketAddr;
+use std::sync::RwLock;
+use std::sync::Arc;
+use std::sync::atomic::{AtomicUsize, Ordering};
+
+#[derive(Debug)]
+pub struct Backend {
+    pub id: String,
+    pub address: SocketAddr,
+    pub active_connections: AtomicUsize,
+}
+
+impl Backend {
+    pub fn new(id: String, address: SocketAddr) -> Self {
+        Self {
+            id: id.to_string(),
+            address,
+            active_connections: AtomicUsize::new(0),
+        }
+    }
+
+    // Ordering::Relaxed means the ops could be in any order, but since this
+    // is just a metric, and we assume the underlying system is sane
+    // enough not to behave poorly, so SeqCst is probably overkill.
+    pub fn inc_connections(&self) {
+        self.active_connections.fetch_add(1, Ordering::Relaxed);
+        println!("{} has {} connections open", self.id, self.active_connections.load(Ordering::Relaxed));
+    }
+
+    pub fn dec_connections(&self) {
+        self.active_connections.fetch_sub(1, Ordering::Relaxed);
+        println!("{} has {} connections open", self.id, self.active_connections.load(Ordering::Relaxed));
+    }
+}
+
+impl fmt::Display for Backend {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{} ({})", self.address, self.id)
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct BackendPool {
+    pub backends: Arc<RwLock<Vec<Arc<Backend>>>>,
+}
+
+impl BackendPool {
+    pub fn new() -> Self {
+        BackendPool {
+            backends: Arc::new(RwLock::new(Vec::new())),
+        }
+    }
+
+    pub fn add(&self, backend: Backend) {
+        self.backends.write().unwrap().push(Arc::new(backend));
+    }
+}

src/balancer/mod.rs

@@ -0,0 +1,9 @@
+pub mod round_robin;
+
+use std::fmt::Debug;
+use std::sync::Arc;
+use crate::backend::Backend;
+
+pub trait Balancer: Debug + Send + Sync + 'static {
+    fn choose_backend(&mut self) -> Option<Arc<Backend>>;
+}

src/balancer/round_robin.rs

@@ -0,0 +1,33 @@
+use std::sync::{Arc, RwLock};
+use std::fmt::Debug;
+use crate::backend::{Backend, BackendPool};
+use crate::balancer::Balancer;
+
+// only the main thread for receiving connections should be
+// doing the load balancing. alternatively, each thread
+// that handles load balancing should get their own instance.
+#[derive(Debug)]
+pub struct RoundRobinBalancer {
+    pool: BackendPool,
+    index: usize,
+}
+
+impl RoundRobinBalancer {
+    pub fn new(pool: BackendPool) -> RoundRobinBalancer {
+        Self {
+            pool,
+            index: 0,
+        }
+    }
+}
+
+impl Balancer for RoundRobinBalancer {
+    fn choose_backend(&mut self) -> Option<Arc<Backend>> {
+        let backends = self.pool.backends.read().unwrap();
+        if backends.is_empty() { return None; }
+
+        let backend = backends[self.index % backends.len()].clone();
+        self.index = self.index.wrapping_add(1);
+        Some(backend)
+    }
+}

src/config.rs

@@ -0,0 +1,6 @@
+// TODO: "routing" rules
+// backends defined as ip + port
+// define sets of backends
+// allowed set operations for now is just union
+// rules are ip + mask and ports, maps to some of the sets
+//  defined earlier, along with a routing strategy

src/main.rs

@@ -1,31 +1,52 @@
+extern crate core;
+
+mod balancer;
+mod config;
+mod backend;
+mod proxy;
+
 use tokio::net::TcpListener;
 use tokio::io::{AsyncReadExt, AsyncWriteExt};
+use std::sync::Arc;
+use std::sync::atomic::AtomicU64;
+use crate::backend::{Backend, BackendPool};
+use crate::balancer::Balancer;
+use crate::balancer::round_robin::RoundRobinBalancer;
+use crate::proxy::tcp::proxy_tcp_connection;
+
+static NEXT_CONN_ID: AtomicU64 = AtomicU64::new(1);
 
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn std::error::Error>> {
-    let listener = TcpListener::bind("0.0.0.0:8080").await?;
+    let pool = BackendPool::new();
+
+    pool.add(Backend::new(
+        "backend 1".into(),
+        "127.0.0.1:8081".parse().unwrap(),
+    ));
+
+    pool.add(Backend::new(
+        "backend 2".into(),
+        "127.0.0.1:8082".parse().unwrap(),
+    ));
+
+    let mut balancer = RoundRobinBalancer::new(pool.clone());
+
+    let listener = TcpListener::bind("127.0.0.1:8080").await?;
 
     loop {
-        let (mut socket, _) = listener.accept().await?;
+        let (socket, _) = listener.accept().await?;
 
-        tokio::spawn(async move {
-            let mut buf = [0; 1024];
+        let conn_id = NEXT_CONN_ID.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
 
-            loop {
-                let n = match socket.read(&mut buf).await {
-                    Ok(0) => return,
-                    Ok(n) => n,
-                    Err(e) => {
-                        eprintln!("failed to read from socket; err = {:?}", e);
-                        return;
-                    }
-                };
-
-                if let Err(e) = socket.write_all(&buf[0..n]).await {
-                    eprintln!("failed to write to socket; err = {:?}", e);
-                    return;
+        if let Some(backend) = balancer.choose_backend() {
+            tokio::spawn(async move {
+                if let Err(e) = proxy_tcp_connection(conn_id, socket, backend).await {
+                    eprintln!("error: conn_id={} proxy failed: {}", conn_id, e);
                 }
-            }
-        });
+            });
+        } else {
+            eprintln!("error: no backendsd for conn_id={}", conn_id);
+        }
     }
 }

src/proxy/mod.rs

@@ -0,0 +1,43 @@
+use std::net::SocketAddr;
+use std::sync::Arc;
+use std::time::Instant;
+use crate::backend::Backend;
+
+pub mod tcp;
+
+pub struct ConnectionContext {
+    pub id: u64,
+    pub client_addr: SocketAddr,
+    pub start_time: Instant,
+    pub backend: Arc<Backend>,
+    pub bytes_transferred: u64,
+}
+
+impl ConnectionContext {
+    pub fn new(id: u64, client_addr: SocketAddr, backend: Arc<Backend>) -> Self {
+        backend.inc_connections();
+
+        Self {
+            id,
+            client_addr,
+            start_time: Instant::now(),
+            backend,
+            bytes_transferred: 0,
+        }
+    }
+}
+
+impl Drop for ConnectionContext {
+    fn drop(&mut self) {
+        self.backend.dec_connections();
+        let duration = self.start_time.elapsed();
+
+        println!("info: conn_id={} closed. client={} backend={} bytes={} duration={:.2?}",
+            self.id,
+            self.client_addr,
+            self.backend.address,
+            self.bytes_transferred,
+            duration.as_secs_f64()
+        );
+    }
+}

src/proxy/tcp.rs

@@ -0,0 +1,26 @@
+use std::sync::Arc;
+use tokio::io;
+use tokio::net::TcpStream;
+use anywho::Error;
+use crate::backend::Backend;
+use crate::proxy::ConnectionContext;
+
+pub async fn proxy_tcp_connection(connection_id: u64, mut client_stream: TcpStream, backend: Arc<Backend>) -> Result<(), Error> {
+    let client_addr = client_stream.peer_addr()?;
+
+    let mut ctx = ConnectionContext::new(connection_id, client_addr, backend.clone());
+
+    #[cfg(debug_assertions)]
+    println!("info: conn_id={} connecting to {}", connection_id, ctx.backend.id);
+
+    let mut backend_stream = TcpStream::connect(&backend.address).await?;
+
+    let (tx, rx) = io::copy_bidirectional(
+        &mut client_stream,
+        &mut backend_stream,
+    ).await?;
+
+    ctx.bytes_transferred = tx + rx;
+
+    Ok(())
+}