Fix FrankenPHP worker mode stalls with explicit workers, wider jitter and Redis sessions

- Set explicit 12 workers in Caddyfile instead of relying on default
- Widen worker restart jitter from ±20% to ±50% to prevent thundering herd
- Add Redis PHP extension to Dockerfile
- Switch session handler from file-based to Redis (db 4) to eliminate file locking
- Add REDIS_HOST env and host.docker.internal to both containers

Author: dereuromark

config/app_custom.php

@@ -49,6 +49,16 @@
 		'logger' => ErrorLogger::class,
 	],
 
+	'Cache' => [
+		'session' => [
+			'className' => \Cake\Cache\Engine\RedisEngine::class,
+			'host' => env('REDIS_HOST', '127.0.0.1'),
+			'database' => 4,
+			'prefix' => 'sandbox_session_',
+			'duration' => '+1 week',
+		],
+	],
+
 	'Log' => [
 		'debug' => [
 			//'className' => 'File',
@@ -95,7 +105,10 @@
 	],
 
 	'Session' => [
-		//'defaults' => 'database',
+		'defaults' => 'cache',
+		'handler' => [
+			'config' => 'session',
+		],
 		'timeout' => 60000,
 		'ini' => [
 			'session.cookie_lifetime' => WEEK,

docker/Caddyfile

@@ -34,6 +34,6 @@
 
     # PHP handling via FrankenPHP in worker mode
     php_server {
-        worker /app/webroot/worker.php
+        worker /app/webroot/worker.php 12
     }
 }

docker/Dockerfile

@@ -15,7 +15,8 @@ RUN install-php-extensions \
     pdo_mysql \
     zip \
     opcache \
-    gd
+    gd \
+    redis
 
 # PHP configuration
 RUN echo "upload_max_filesize = 32M" >> /usr/local/etc/php/conf.d/uploads.ini \

docker/docker-compose.yml

@@ -18,6 +18,9 @@ services:
       - MERCURE_PUBLISHER_JWT_KEY=${MERCURE_PUBLISHER_JWT_KEY}
       - MERCURE_SUBSCRIBER_JWT_KEY=${MERCURE_SUBSCRIBER_JWT_KEY}
       - MERCURE_EXTRA_DIRECTIVES=anonymous
+      - REDIS_HOST=host.docker.internal
+    extra_hosts:
+      - "host.docker.internal:host-gateway"
     security_opt:
       - no-new-privileges:true
     cap_add:
@@ -38,6 +41,9 @@ services:
     environment:
       - MERCURE_PUBLISHER_JWT_KEY=${MERCURE_PUBLISHER_JWT_KEY}
       - MERCURE_SUBSCRIBER_JWT_KEY=${MERCURE_SUBSCRIBER_JWT_KEY}
+      - REDIS_HOST=host.docker.internal
+    extra_hosts:
+      - "host.docker.internal:host-gateway"
     security_opt:
       - no-new-privileges:true
 

webroot/worker.php

@@ -30,9 +30,9 @@
 $server = new Server($app);
 
 // Max requests before worker restarts (prevents memory leaks)
-// Add jitter to prevent all workers restarting simultaneously (thundering herd)
+// Add wide jitter to prevent all workers restarting simultaneously (thundering herd)
 $maxRequests = (int)($_SERVER['MAX_REQUESTS'] ?? 500);
-$maxRequests = random_int((int)($maxRequests * 0.8), (int)($maxRequests * 1.2));
+$maxRequests = random_int((int)($maxRequests * 0.5), (int)($maxRequests * 1.5));
 
 // Handle requests in a loop
 for ($requestCount = 0; $requestCount < $maxRequests; $requestCount++) {