Trouble deploying Symfony3 on a new server - php

Question

I have used Symfony a lot in the past and haven't had many problems. I have been trying to deploy it on a different server (Ubuntu 16 w/ Apache) and am having a lot of issues.
I am getting 500 error now (https://bereanboard.com/app_dev.php). What I have tried is to go to *.com/config.php and *.com/app_dev.php to see issues (I had to temporarily comment out the section that forbids access from non localhost). I have also been checking the Apache error.log and Symfony's var/logs/prod.log.
Keep in mind it works fine on local MAMP and on my previous CentOS.
First, I am for the first time encountering permission problems for var/cache and var/logs. This was pretty easy to fix with commands like chmod -R 777 var/cache. But why did this issue come up only on this new server? Anyway, config.php on the new server is now telling me "All checks passed".
Second, in var/logs/prod.log I am getting all sorts of 'Can't find class, did you forget a "use" statement?' errors. Some of these are for a twig extension AppBundle/Twig/AppExtension.php.
Here are some Critical erros:
request.CRITICAL: Uncaught PHP Exception InvalidArgumentException:
"Class "AppBundle\Controller\HomeController" does not exist." at
/home/travis/var/cache/prod/classes.php line 4872
{"exception":"[object] (InvalidArgumentException(code: 0): Class
\"AppBundle\Controller\HomeController\" does not exist. at
/home/travis/var/cache/prod/classes.php:4872)"} []
and
php.CRITICAL: Class 'AppBundle\Twig\AppExtension' not found
{"exception":"[object]
(Symfony\Component\Debug\Exception\FatalThrowableError(code: 0):
Class 'AppBundle\Twig\AppExtension' not found at
/home/travis/var/cache/prod/appProdProjectContainer.php:2881)"} []
[2017-01-19 06:35:03] request.CRITICAL: Uncaught PHP Exception
Symfony\Component\Debug\Exception\ClassNotFoundException: "Attempted
to load class "AppExtension" from namespace "AppBundle\Twig". Did you
forget a "use" statement for another namespace?" at
/home/travis/var/cache/prod/appProdProjectContainer.php line 2881
{"exception":"[object]
(Symfony\Component\Debug\Exception\ClassNotFoundException(code:
0): Attempted to load class \"AppExtension\" from namespace
\"AppBundle\Twig\".\nDid you forget a \"use\" statement for another
namespace? at
/home/travis/var/cache/prod/appProdProjectContainer.php:2881)"} []
[2017-01-19 06:35:03] request.CRITICAL: Exception thrown when handling
an exception
(Symfony\Component\Cache\Exception\InvalidArgumentException: Cache
directory is not writable
(/home/travis/var/cache/prod/pools/CtBqbs+VrF) at
/home/travis/var/cache/prod/classes.php line 1194)
{"exception":"[object]
(Symfony\Component\Cache\Exception\InvalidArgumentException(code:
0): Cache directory is not writable
(/home/travis/var/cache/prod/pools/CtBqbs+VrF) at
/home/travis/var/cache/prod/classes.php:1194)"} []
Also, it's worth mentioning that that a fresh, empty project made from the command symfony new project does work.
*EDIT
I have consulted these Symfony docs. I have tried every way of clearing cache that I could find.
*EDIT
Here is services.yml
services:
app.twig_extension:
class: AppBundle\Twig\AppExtension
arguments: ["#doctrine.orm.entity_manager", "#security.token_storage"]
public: false
tags:
- { name: twig.extension }

Answer 1

It seems that there is an access problem for your web server.
Check user which launching apache on Centos by
# egrep -i '^user|^group' /etc/httpd/conf/httpd.conf
It should return apache
Then give the good privilege to /home/travis directory:
Option 1: You could have a look on Stack Echange / AskUbuntu and adapt it with apache user instead of www-data
Option 2: With first option, if you've created a folder, Apache cannot write to it. This can be "fixed" by setting umask 0007 and adding yourself (travis) to the Apache group, so that newly created files and folders are writeable by the group.
Option 2 is better if ou have enough privileges to change mask.

Answer 2

Try to clear cache :
php bin/console cache:clear --env=prod
and set files permissions :
chmod -R 777 var/cache
chmod -R 777 var/logs
chmod -R 777 var/sessions
hope this help you.

Answer 3

I had faced the same problem before once. You will have to complete remove the vendor folder
rm -R vendor/
and freshly install all the dependencies again.
php composer.phar install
This will resolve the issue.