title: AppEngine - Client closed keepalive connection
body: <p>I have deployed my Symfony 4 app to Google App Engine (Flexible environment).</p>
  
  <p>The build seems to have worked, but loading the app on in Chrome results in error:</p>
  
  <pre><code>Oops! An Error Occurred
  The server returned a "500 Internal Server Error".
  Something is broken. Please let us know what you were doing when this error occurred. We will fix it as soon as possible. Sorry for any inconvenience caused.
  </code></pre>
  
  <p>The app engine log is here:</p>
  
  <pre><code> 2019/02/02 04:33:13 [info] 9#9: *6 client 172.17.0.4 closed keepalive connection
   A 
   GET 404 191 B 0 ms Chrome 71 /favicon.ico A  GET 404 191 B 0 ms Chrome 71
   GET 500 930 B 6 ms Chrome 71 /connect/google A  GET 500 930 B 6 ms Chrome 71
   GET 307 316 B 6 ms Chrome 71 / A  GET 307 316 B 6 ms Chrome 71
   172.17.0.4 - - [02/Feb/2019:04:32:13 +0000] "GET /connect/google HTTP/1.1" 500 930 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36"
   A 
   172.17.0.4 - - [02/Feb/2019:04:32:13 +0000] "GET / HTTP/1.1" 307 316 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36"
   A 
   2019/02/02 04:29:08 [info] 9#9: *1 client 172.17.0.4 closed keepalive connection
   A 
   GET 500 930 B 6 ms Chrome 71 /connect/google A  GET 500 930 B 6 ms Chrome 71
   GET 307 316 B 5 ms Chrome 71 / A  GET 307 316 B 5 ms Chrome 71
   172.17.0.4 - - [02/Feb/2019:04:28:08 +0000] "GET /connect/google HTTP/1.1" 500 930 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36"
   A 
   172.17.0.4 - - [02/Feb/2019:04:28:08 +0000] "GET / HTTP/1.1" 307 316 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36"
   A 
   GET 404 191 B 10 ms Chrome 71 /favicon.ico A  GET 404 191 B 10 ms Chrome 71
   GET 500 930 B 207 ms Chrome 71 /connect/google A  GET 500 930 B 207 ms Chrome 71
   172.17.0.4 - - [02/Feb/2019:04:27:50 +0000] "GET /connect/google HTTP/1.1" 500 930 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36"
   A 
   GET 307 316 B 271 ms Chrome 71 / A  GET 307 316 B 271 ms Chrome 71
   172.17.0.4 - - [02/Feb/2019:04:27:49 +0000] "GET / HTTP/1.1" 307 316 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36"
   A 
  A  2019-02-02 03:22:43,817 INFO success: nginx entered RUNNING state, process has stayed up for &gt; than 1 seconds (startsecs)
  
  A  2019-02-02 03:22:43,817 INFO success: php-fpm entered RUNNING state, process has stayed up for &gt; than 1 seconds (startsecs)
  
  A  [02-Feb-2019 03:22:42] NOTICE: ready to handle connections
  
  A  [02-Feb-2019 03:22:42] NOTICE: fpm is running, pid 7
  
  A  2019/02/02 03:22:42 [notice] 8#8: start worker process 9
  
  A  2019/02/02 03:22:42 [notice] 8#8: start worker processes
  
  A  2019/02/02 03:22:42 [notice] 8#8: getrlimit(RLIMIT_NOFILE): 65536:65536
  
  A  2019/02/02 03:22:42 [notice] 8#8: OS: Linux 4.9.0-8-amd64
  
  A  2019/02/02 03:22:42 [notice] 8#8: nginx/1.10.3 (Ubuntu)
  
  A  2019/02/02 03:22:42 [notice] 8#8: using the "epoll" event method
  
  A  2019-02-02 03:22:42,339 INFO spawned: 'nginx' with pid 8
  
  A  2019-02-02 03:22:42,338 INFO spawned: 'php-fpm' with pid 7
  
  A  2019-02-02 03:22:41,335 INFO supervisord started with pid 1
  
  A  2019-02-02 03:22:41,329 WARN No file matches via include "/etc/supervisor/conf.d/*.conf"
  
  A  2019-02-02 03:22:41,329 CRIT Supervisor running as root (no user in config file)
  </code></pre>
  
  <p>I don't understand this error. How can I resolve?</p>