Symfony 4 on Google App Eng (flex) - 500 error - php

Question

Symfony 4 app running on Google App Eng (flex).
I deployed the app, but I am getting a 500 error, and app engine is providing no additional detail.
The deploy process I did was as follows:
(Following doc https://cloud.google.com/community/tutorials/run-symfony-on-appengine-flexible)
Include an app.yaml file as follows:
runtime: php
env: flex
runtime_config:
document_root: public
front_controller_file: index.php
env_variables:
APP_ENV: "prod"
manual_scaling:
instances: 1
resources:
cpu: 1
memory_gb: 0.5
disk_size_gb: 10
Update the composer line:
"post-install-cmd": [
"chmod -R ug+w $APP_DIR/var"
],
Cleared cache and warmed cache for production:
php bin/console cache:clear --env=prod --no-debug
php bin/console cache:warmup --env=prod --no-debug
Even though I haven't done the doctrine set up part, I should be able to go to xxxx.appspot.com and get the home page. Instead I get ...
xxxx.appspot.com is currently unable to handle this request. HTTP ERROR 500
This is puzzling because the app worked totally fine locally before warming the cache.
Am I deploying correctly or forgetting something? (I cant get any detail on error from App Engine).
Edit
I have checked the var/log local folder and found dev.log and prod.deprecations.log. In the latter I have this error many times ...
[2018-10-15 11:28:59] php.INFO: User Deprecated: Referencing controllers with a single colon is deprecated since Symfony 4.1, use "fos_user.security.controller::loginAction" instead. {"exception":"[object] (ErrorException(code: 0): User Deprecated: Referencing controllers with a single colon is deprecated since Symfony 4.1, use \"fos_user.security.controller::loginAction\" instead. at C:\\dev\\projects\\jw-app\\vendor\\symfony\\framework-bundle\\Routing\\DelegatingLoader.php:98)"}

Answer 1

Based on the new edit information you’ve just provided it seems that the issue you are encountering is more on the Symfony version you are using than GAE.
Symfony 4.1 has deprecated the bundle notation. This means that it is no longer recommended to organize your business logic using bundles. You can see some examples of this on the official Symfony web page here.
Your error message tells you to use the following:
\"fos_user.security.controller::loginAction\
For the file at path:
C:\dev\projects\jw-app\vendor\symfony\framework-bundle\Routing\DelegatingLoader.php:98)
on line 98
It seems a few people have the following referencing issues with Symfony 4.1 as well. You can view the details of their similar issue and review recommended fixes at FriendsOfSymfony Github page.
Also, I would like to mention that since you are using GAE:Flex you can view your build history and error logs for your project at the following:
Google Cloud Build ( Google Cloud Console > Open the menu > tools > Cloud Build )
This will provide you the necessary information of the build you are trying to deploy on GAE.