I'm running Laravel 5.4 project, and hosted under google cloud project. In order to test the same I have used dev_appserver.py app.yaml --runtime=php55 it initiates the program but it throws the error displayed

Warning: require(/Users/Avi/Documents/.../website/PLACEHOLDER): failed to open stream: No such file or directory in /Users/Avi/Downloads/google-cloud-sdk/platform/google_appengine/google/appengine/tools/devappserver2/php/setup.php on line 147

Fatal error: require(): Failed opening required '/Users/Avi/Documents/.../website/PLACEHOLDER' (include_path='.:/Users/Avi/Documents/.../website:/Users/Avi/Downloads/google-cloud-sdk/platform/google_appengine/php/sdk') in /Users/Avi/Downloads/google-cloud-sdk/platform/google_appengine/google/appengine/tools/devappserver2/php/setup.php on line 147

App.yaml

  runtime: custom
env: flex

runtime_config:
  document_root: public

# Ensure we skip ".env", which is only for local development
skip_files:
  - .env

env_variables:
  # Put production environment variables here.
  APP_LOG: errorlog
  APP_KEY: base64:...
  STORAGE_DIR: /tmp
  CACHE_DRIVER: file
  SESSION_DRIVER: file

I'm not able to figure out what's "PLAEHOLDER" and how to resolve the error so that the following laravel project can be hosted locally for development phase.

TIA

I encountered the same error with some config settings I used.

my app.yaml file worked with php runtime:

runtime: php
env: flex

runtime_config:
  document_root: public

# Ensure we skip ".env", which is only for local development
skip_files:
  - .env

env_variables:
  # Put production environment variables here.
  APP_LOG: errorlog
  APP_KEY: your_key
  STORAGE_DIR: /tmp

I couldn't get the standard environment to work with php, if anyone can, show us how :)

You are trying to use the local testing methodology from the standard environment to your flexible environment app. The local devserver doesn't support flexible apps - hence the error.

From The PHP Development Server:

Note: dev_appserver.py does not run in the App Engine flexible environment.

Related: How to tell if a Google App Engine documentation page applies to the standard or the flexible environment

This is the doc you need to follow: Running locally.