From 889b866c82e6ce965a12bb390782db46259d06db Mon Sep 17 00:00:00 2001
From: Charles Duffy <charles@dyfis.net>
Date: Thu, 2 Oct 2025 10:41:29 -0500
Subject: [PATCH] nixos/nats: Shut down gracefully, and prevent automatic
 restart on deliberate stop

SIGUSR2 puts nats-server into "lame-duck mode", where the node hands off leader roles and hands clients off to other nodes.
---
 nixos/modules/services/networking/nats.nix | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/nixos/modules/services/networking/nats.nix b/nixos/modules/services/networking/nats.nix
index 57765c9d2449..4508fdc1f339 100644
--- a/nixos/modules/services/networking/nats.nix
+++ b/nixos/modules/services/networking/nats.nix
@@ -138,7 +138,15 @@ in
           Type = "simple";
           ExecStart = "${pkgs.nats-server}/bin/nats-server -c ${configFile}";
           ExecReload = "${pkgs.coreutils}/bin/kill -HUP $MAINPID";
-          ExecStop = "${pkgs.coreutils}/bin/kill -SIGINT $MAINPID";
+
+          KillMode = "mixed";
+          KillSignal = "SIGUSR2";
+          SuccessExitStatus = [
+            0
+            "SIGUSR2"
+          ];
+
+          TimeoutStopSec = "150"; # must exceed lame_duck_duration, which defaults to 2min
           Restart = "on-failure";
 
           User = cfg.user;