optional external script during graceful shutdown

web3_proxy/src/block_number.rs

@@ -222,6 +222,7 @@ impl From<&Web3ProxyBlock> for BlockNumOrHash {
     }
 }
 
+/// TODO: have another type that contains &mut Value of the block_needed or from_block+to_block. this will make it easier to modify the request
 /// TODO: change this to also return the hash needed?
 /// this replaces any "latest" identifiers in the JsonRpcRequest with the current block number which feels like the data is structured wrong
 #[derive(Debug, Default, Hash, Eq, PartialEq)]

web3_proxy/src/config.rs

@@ -203,6 +203,12 @@ pub struct AppConfig {
     /// the stats page url for a logged in user. if set, must contain "{rpc_key_id}"
     pub redirect_rpc_key_url: Option<String>,
 
+    /// optional script to run before shutting the frontend down.
+    /// this is useful for keeping load balancers happy.
+    pub shutdown_script: Option<String>,
+    /// optional arguments for your shutdown script.
+    pub shutdown_script_args: Vec<String>,
+
     /// Optionally send errors to <https://sentry.io>
     pub sentry_url: Option<Dsn>,
 

web3_proxy/src/frontend/mod.rs

@@ -24,10 +24,10 @@ use std::sync::Arc;
 use std::{iter::once, time::Duration};
 use std::{net::SocketAddr, sync::atomic::Ordering};
 use strum::{EnumCount, EnumIter};
-use tokio::sync::broadcast;
+use tokio::{process::Command, sync::broadcast};
 use tower_http::sensitive_headers::SetSensitiveRequestHeadersLayer;
 use tower_http::{cors::CorsLayer, normalize_path::NormalizePathLayer, trace::TraceLayer};
-use tracing::{error_span, info, trace_span};
+use tracing::{error, error_span, info, trace_span};
 use ulid::Ulid;
 
 #[cfg(feature = "listenfd")]
@@ -364,6 +364,22 @@ pub async fn serve(
         // TODO: option to use with_connect_info. we want it in dev, but not when running behind a proxy, but not
         .with_graceful_shutdown(async move {
             let _ = shutdown_receiver.recv().await;
+
+            if let Some(shutdown_script) = app.config.shutdown_script.as_ref() {
+                let shutdown_script = Command::new(shutdown_script)
+                    .args(&app.config.shutdown_script_args)
+                    .spawn()
+                    .expect("failed to execute script");
+
+                match shutdown_script.wait_with_output().await {
+                    Ok(x) => {
+                        info!(?x, "shutdown script finished");
+                    }
+                    Err(err) => {
+                        error!(?err, "shutdown script failed");
+                    }
+                };
+            }
         })
         .await
         .map_err(Into::into);