Slow rollout feature

Cargo.toml

@@ -46,6 +46,7 @@ url = "2.5"
 metrics-util = "0.19.0"
 eyre = "0.6.12"
 paste = "1.0.15"
+rand = "0.8.5"
 
 # dev dependencies for integration tests
 parking_lot = "0.12.3"

src/bin/main.rs

@@ -105,6 +105,7 @@ async fn main() -> eyre::Result<()> {
         boost_sync_enabled,
         args.execution_mode,
         flashblocks_client,
+        args.rollout_pct,
     );
 
     // Spawn the debug server

src/cli.rs

@@ -73,6 +73,10 @@ pub struct Args {
     /// Enable Flashblocks client
     #[clap(flatten)]
     pub flashblocks: FlashblocksArgs,
+
+    /// Percentage of blocks built by the builder
+    #[arg(long, env, default_value = "100")]
+    pub rollout_pct: u16,
 }
 
 #[derive(Parser, Debug)]

src/server.rs

@@ -124,6 +124,7 @@ pub struct RollupBoostServer {
     pub payload_trace_context: Arc<PayloadTraceContext>,
     pub flashblocks_client: Option<Arc<FlashblocksService>>,
     pub execution_mode: Arc<Mutex<ExecutionMode>>,
+    pub rollout_pct: u16,
 }
 
 impl RollupBoostServer {
@@ -133,6 +134,7 @@ impl RollupBoostServer {
         boost_sync: bool,
         initial_execution_mode: ExecutionMode,
         flashblocks_client: Option<FlashblocksService>,
+        rollout_pct: u16,
     ) -> Self {
         Self {
             l2_client: Arc::new(l2_client),
@@ -141,6 +143,7 @@ impl RollupBoostServer {
             payload_trace_context: Arc::new(PayloadTraceContext::new()),
             flashblocks_client: flashblocks_client.map(Arc::new),
             execution_mode: Arc::new(Mutex::new(initial_execution_mode)),
+            rollout_pct,
         }
     }
 
@@ -596,6 +599,15 @@ impl RollupBoostServer {
                 ));
             }
 
+            if !should_rollout(self.rollout_pct) {
+                // Skip due to slow rollout
+                return Err(ErrorObject::owned(
+                    INVALID_REQUEST_CODE,
+                    "Skipped because of (self.rollout_pct)% slow rollout",
+                    None::<String>,
+                ));
+            }
+
             if let Some(cause) = self.payload_trace_context.trace_id(&payload_id) {
                 tracing::Span::current().follows_from(cause);
             }
@@ -673,11 +685,21 @@ impl RollupBoostServer {
             "number" = %block_number,
             %context,
             %payload_id,
+            "rollout_pct" = self.rollout_pct,
         );
         Ok(payload)
     }
 }
 
+/// Returns true if the rollout percentage is 100 or if the random number is less than the rollout percentage
+fn should_rollout(rollout_pct: u16) -> bool {
+    if rollout_pct == 100 {
+        true
+    } else {
+        rand::random::<f64>() < rollout_pct as f64 / 100.0
+    }
+}
+
 #[cfg(test)]
 #[allow(clippy::complexity)]
 mod tests {
@@ -796,6 +818,7 @@ mod tests {
                 boost_sync,
                 ExecutionMode::Enabled,
                 None,
+                100,
             );
 
             let module: RpcModule<()> = rollup_boost_client.try_into().unwrap();
@@ -837,6 +860,7 @@ mod tests {
         boost_sync_enabled().await;
         builder_payload_err().await;
         test_local_external_payload_ids_same().await;
+        test_should_rollout();
     }
 
     async fn engine_success() {
@@ -1100,4 +1124,32 @@ mod tests {
 
         test_harness.cleanup().await;
     }
+
+    fn test_should_rollout() {
+        // Test with 100% rollout - should always return true
+        for _ in 0..100 {
+            assert!(
+                should_rollout(100),
+                "100% rollout should always return true"
+            );
+        }
+
+        // Test with 0% rollout - should always return false
+        for _ in 0..100 {
+            assert!(!should_rollout(0), "0% rollout should always return false");
+        }
+
+        // Test with 50% rollout - should be statistically around 50%
+        let trials = 1000;
+        let successes = (0..trials).filter(|_| should_rollout(50)).count();
+
+        let success_rate = successes as f64 / trials as f64;
+
+        // With 1000 trials, we should be within 5% of expected 50%
+        assert!(
+            (success_rate - 0.5).abs() < 0.05,
+            "Expected success rate near 50%, got {}%",
+            success_rate * 100.0
+        );
+    }
 }