Unable to get Google App Engine PHP tutorial working - google-app-engine

Question

I'm following the GAE PHP tutorial but I can't get the local dev server to respond properly.
I run it with
dev_appserver.py --php_executable_path=/usr/bin/php --host=192.168.33.44 ./
and it starts up fine. When I view http://192.168.33.44:8080/ the logs show
INFO 2016-10-12 07:55:06,264 module.py:788] default: "GET / HTTP/1.1" 200 -
but I get a blank page. There's nothing in the tutorial explaining what to do if you have problems.
So far, I've:
Tried PHP 5.5 and 5.6 (remi): no difference
Put corrupt PHP in helloworld.php: no errors
Changed the handler to - url: /: blank page on /, 404 page for any other URL
Scoured Google Docs: no help
Scoured Google: no help
Asked the rubber duck: no help
I'm running Centos 7.2 via Vagrant and Google Cloud SDK 129.0.0.
Any and all help greatly appreciated.
[EDIT]
Additional data as requested
$ which php
/usr/bin/php
$ /usr/bin/php -v
PHP 5.5.38 (cli) (built: Sep 19 2016 13:45:10)
Copyright (c) 1997-2015 The PHP Group
Zend Engine v2.5.0, Copyright (c) 1998-2015 Zend Technologies
$ which python
/usr/bin/python
$ /usr/bin/python -V
Python 2.7.5
$ cat app.yaml
runtime: php55
api_version: 1
handlers:
- url: /.*
script: helloworld.php
$ cat helloworld.php
<?php
echo 'Hello, World!';
$ dev_appserver.py --php_executable_path=/usr/bin/php --host=192.168.33.44 ./
Updates are available for some Cloud SDK components. To install them, please run:
$ gcloud components update
INFO 2016-10-13 08:21:22,699 devappserver2.py:769] Skipping SDK update check.
INFO 2016-10-13 08:21:22,730 api_server.py:205] Starting API server at: http://localhost:46453
INFO 2016-10-13 08:21:22,737 dispatcher.py:197] Starting module "default" running at: http://192.168.33.44:8080
INFO 2016-10-13 08:21:22,738 admin_server.py:116] Starting admin server at: http://localhost:8000
INFO 2016-10-13 08:21:34,142 module.py:788] default: "GET / HTTP/1.1" 200 -
Response Headers from Chrome when accessing http://192.168.33.44:8080/
Cache-Control: no-cache
Content-Length: 0
Content-Type: text/html
Date: Thu, 13 Oct 2016 08:21:34 GMT
Expires: Fri, 01 Jan 1990 00:00:00 GMT
Server: Development/2.0
I updated from 129 to 130 but the same problem exists

Answer 1

Turns out the problem was a trivial oversight...
dev_appserver.py --php_executable_path=/usr/bin/php --host=192.168.33.44 ./
Should have been
dev_appserver.py --php_executable_path=/usr/bin/php-cgi --host=192.168.33.44 ./
The App Engine requires the php-cgi binary, not the cli one. Ended up stumbling over it in the docs a while ago, but forgot to come back here and post the answer