Add signal handler and shutdown hook (#232)

When the application is running in a container, it is given PID 1 which
means it does not automatically get given signal handlers and can't be
killed. When running the container in the foreground this stops Ctrl-C
from interrupting it while in kubernetes it means the graceful shutdown
always times out resulting in the container eventually being forcibly
deleted, killing the process.

Adding an explicit handler for the common signals used to interrupt
processes means that Ctrl-C, kubernetes and `podman stop` all work as
expected.

Author: tpoliaw

src/graphql/mod.rs

@@ -36,6 +36,8 @@ use axum_extra::TypedHeader;
 use chrono::{Datelike, Local};
 use derive_more::{Display, Error};
 use tokio::net::TcpListener;
+use tokio::select;
+use tokio::signal::unix::{signal, SignalKind};
 use tracing::{debug, info, instrument, trace, warn};
 
 use crate::build_info::ServerStatus;
@@ -95,10 +97,23 @@ pub async fn serve_graphql(opts: ServeOptions) {
         .await
         .unwrap_or_else(|e| panic!("Could not listen on {:?}:{}: {e}", addr.0, addr.1));
     axum::serve(listener, app)
+        .with_graceful_shutdown(create_signal_handler())
         .await
         .expect("Can't serve graphql endpoint");
 }
 
+async fn create_signal_handler() {
+    let mut term = signal(SignalKind::terminate()).expect("Failed to create SIGTERM listener");
+    let mut int = signal(SignalKind::interrupt()).expect("Failed to create SIGINT listener");
+    let mut quit = signal(SignalKind::quit()).expect("Failed to create SIGQUIT listener");
+    let sig = select! {
+        _ = term.recv() => "SIGTERM",
+        _ = int.recv() => "SIGINT",
+        _ = quit.recv() => "SIGQUIT",
+    };
+    info!("Server interrupted by {sig}");
+}
+
 pub fn graphql_schema<W: Write>(mut out: W) -> Result<(), std::io::Error> {
     let schema = Schema::new(Query, Mutation, EmptySubscription);
     write!(out, "{}", schema.sdl())