index.ts

//…
    // Add readiness endpoint
    let isShuttingDown = false;
    app.use(
      async (ctx, next): Promise<void> => {
        if (ctx.request.path === "/_ready" || ctx.request.path === "/_ready/") {
          if (isShuttingDown) {
            ctx.status = 503;
            ctx.set("Connection", "close");
            ctx.body = "not ready";
            return;
          }

          ctx.response.body = "ready";
          return;
        }

        return next();
      }
    );

    // Add graceful shutdown.
    process.on("SIGTERM", function gracefulExit(): void {
      if (isShuttingDown) {
        console.error(
          formatLogEntry(
            new Error("Received second SIGTERM; forceful shutdown initiated."),
            null,
            "NOTICE"
          )
        );
        process.exit(1);
        return;
      }

      isShuttingDown = true;
      console.error(
        formatLogEntry(
          new Error("Received SIGTERM; graceful shutdown initiated."),
          null,
          "NOTICE"
        )
      );

      // If we're still running after 25 seconds from the signal, force shutdown.
      setTimeout((): void => {
        console.error(
          formatLogEntry(
            new Error(
              "Not all connections have closed in time; forceful shutdown initiated."
            ),
            null,
            "WARNING"
          )
        );
        process.exit(1);
      }, 25000);

      // Kubernetes doesn't wait for service discovery to change before sending the
      // SIGTERM, so we don't want to immediately close the server to new
      // connections. We'll immediately start failing readiness checks but continue
      // to accept new requests for 20 seconds after the signal.
      setTimeout(async (): Promise<void> => {
        console.info(
          formatLogEntry(
            "Readiness delay complete; continuing graceful shutdown.",
            null,
            "NOTICE"
          )
        );

        // Now, 20 seconds after the signal, we will close the server to new
        // connections, and wait for established connections to close.
        await Promise.all([
          authx.pool.end(),
          new Promise((resolve): void => void server.close(resolve))
        ]);

        console.info(
          formatLogEntry("Graceful shutdown complete.", null, "NOTICE")
        );
        process.exit(0);
      }, 20000);
    });
//…