From 53df1ce22c6d21cf02a80a9d09b083b353114588 Mon Sep 17 00:00:00 2001
From: Daniel Widgren <daniel.widgren@gmail.com>
Date: Tue, 10 Mar 2026 22:20:08 +0100
Subject: [PATCH 1/2] feat: add graceful shutdown for k8s deployments

Add nova:graceful_shutdown/0 that suspends the ranch listener, drains
active connections with a configurable timeout, then stops the listener.
Called automatically via prep_stop/1 during application shutdown.

Configurable via sys.config:
- shutdown_delay: ms to wait before suspending (default 0)
- shutdown_drain_timeout: max ms to wait for connections to drain (default 15000)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 src/nova.erl     | 50 +++++++++++++++++++++++++++++++++++++++++++++++-
 src/nova_app.erl |  7 +++++--
 2 files changed, 54 insertions(+), 3 deletions(-)

diff --git a/src/nova.erl b/src/nova.erl
index b88f259c..1622ee1d 100644
--- a/src/nova.erl
+++ b/src/nova.erl
@@ -5,6 +5,8 @@
 
 -module(nova).
 
+-include_lib("kernel/include/logger.hrl").
+
 -export([
          get_main_app/0,
          get_apps/0,
@@ -13,7 +15,8 @@
          set_env/2,
          use_stacktrace/1,
          format_stacktrace/1,
-         detect_language/0
+         detect_language/0,
+         graceful_shutdown/0
         ]).
 
 -type state() :: any().
@@ -127,6 +130,51 @@ format_stacktrace(Stacktrace) ->
 %% of the Elixir and LFE modules, and returns the language.
 %% @end
 %%--------------------------------------------------------------------
+-spec graceful_shutdown() -> ok.
+graceful_shutdown() ->
+    Delay = application:get_env(nova, shutdown_delay, 0),
+    case Delay > 0 of
+        true ->
+            ?LOG_NOTICE(#{msg => <<"Graceful shutdown started">>, delay_ms => Delay}),
+            timer:sleep(Delay);
+        false ->
+            ok
+    end,
+    ?LOG_NOTICE(#{msg => <<"Suspending listener">>}),
+    ranch:suspend_listener(nova_listener),
+    DrainTimeout = application:get_env(nova, shutdown_drain_timeout, 15000),
+    ?LOG_NOTICE(#{msg => <<"Draining connections">>, timeout_ms => DrainTimeout}),
+    drain_connections(DrainTimeout),
+    ?LOG_NOTICE(#{msg => <<"Stopping listener">>}),
+    cowboy:stop_listener(nova_listener),
+    ok.
+
+drain_connections(Timeout) ->
+    Deadline = erlang:monotonic_time(millisecond) + Timeout,
+    drain_loop(Deadline).
+
+drain_loop(Deadline) ->
+    case ranch:info(nova_listener) of
+        Info when is_list(Info) ->
+            case proplists:get_value(active_connections, Info, 0) of
+                0 ->
+                    ok;
+                N ->
+                    Now = erlang:monotonic_time(millisecond),
+                    case Now >= Deadline of
+                        true ->
+                            ?LOG_WARNING(#{msg => <<"Drain timeout reached">>,
+                                           remaining_connections => N}),
+                            ok;
+                        false ->
+                            timer:sleep(500),
+                            drain_loop(Deadline)
+                    end
+            end;
+        _ ->
+            ok
+    end.
+
 -spec detect_language() -> elixir | lfe | erlang.
 detect_language() ->
     case {code:which('Elixir.System'), code:which(lfe_eval)} of
diff --git a/src/nova_app.erl b/src/nova_app.erl
index 511b330e..ed5594d3 100644
--- a/src/nova_app.erl
+++ b/src/nova_app.erl
@@ -9,7 +9,7 @@
 -behaviour(application).
 
 %% Application callbacks
--export([start/2, stop/1]).
+-export([start/2, prep_stop/1, stop/1]).
 
 %%====================================================================
 %% API
@@ -18,7 +18,10 @@
 start(_StartType, _StartArgs) ->
     nova_sup:start_link().
 
-%%--------------------------------------------------------------------
+prep_stop(State) ->
+    nova:graceful_shutdown(),
+    State.
+
 stop(_State) ->
     ok.
 

From 257c93a11793ca829bf00c68183ac518144e4f7e Mon Sep 17 00:00:00 2001
From: Daniel Widgren <daniel.widgren@gmail.com>
Date: Tue, 10 Mar 2026 22:45:09 +0100
Subject: [PATCH 2/2] fix: use ranch 2.x map API in drain_loop

ranch:info/1 returns a map in ranch 2.x, not a proplist.
Match on map keys directly to satisfy dialyzer.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 src/nova.erl | 29 ++++++++++++-----------------
 1 file changed, 12 insertions(+), 17 deletions(-)

diff --git a/src/nova.erl b/src/nova.erl
index 1622ee1d..6e39c5d4 100644
--- a/src/nova.erl
+++ b/src/nova.erl
@@ -155,24 +155,19 @@ drain_connections(Timeout) ->
 
 drain_loop(Deadline) ->
     case ranch:info(nova_listener) of
-        Info when is_list(Info) ->
-            case proplists:get_value(active_connections, Info, 0) of
-                0 ->
+        #{active_connections := 0} ->
+            ok;
+        #{active_connections := N} ->
+            Now = erlang:monotonic_time(millisecond),
+            case Now >= Deadline of
+                true ->
+                    ?LOG_WARNING(#{msg => <<"Drain timeout reached">>,
+                                   remaining_connections => N}),
                     ok;
-                N ->
-                    Now = erlang:monotonic_time(millisecond),
-                    case Now >= Deadline of
-                        true ->
-                            ?LOG_WARNING(#{msg => <<"Drain timeout reached">>,
-                                           remaining_connections => N}),
-                            ok;
-                        false ->
-                            timer:sleep(500),
-                            drain_loop(Deadline)
-                    end
-            end;
-        _ ->
-            ok
+                false ->
+                    timer:sleep(500),
+                    drain_loop(Deadline)
+            end
     end.
 
 -spec detect_language() -> elixir | lfe | erlang.