Drupal 8.x

I have a site that was upgraded from Drupal 6 to 7 and now it is finally Drupal 8.1.1 But there are some strange problems.

1) I put the site offline, and now I can't go back online. I get the following error message:

Fatal error: Cannot instantiate interface Drupal\Core\Cache\CacheBackendInterface in /home/mysitename/public_html/core/lib/Drupal/Component/DependencyInjection/Container.php on line 268

2) status report gives me the following problems:

Hi ladies and gents my first post so I hope you are well, and that you dont find this post annoying as i'm sure it will have been asked before but I have now been up all night and its sending me mental as a new Drupal person as of yesterday..

I've looked at so much in the last 24 hours that I'm going boogley eyed but by the end of today if I'm not snapped up for an assistant's post on weight watchers . com or similar with my new knowledge then something is seriously wrong..

However, I digress.. Back to basics... :))

Hi,

Is there any way to modify/customize the response of the RESTful web service (builtin feature) in Drupal 8? I would like to add some additional data in the API response. Please confirm, if there is any way to modify/customize the API responses in Drupal 8.

Thanks,

Hi,

I would like to add a custom user authentication (to check user login using access token) in some of the APIs. The process would be like:

Step 1: The user calls a login API (custom) with username and password. The API will check the user credentials in DB and generate an access token with some random value and return this value as JSON response.

Step 2: The subsequent requests will have this access token (instead of username and password). The API will process the request, only if the access token is valid.

Hey I want to know what you guys think is the the best approach to handling media when you want non technical users to upload and manage there own Images with additional fields in Drupal 8? (In the end a decent Media Manager build)

I have looked at

I'm new to D8, and am trying to create a new theme. I'm stuck on trying to simply add a CSS file/reference globally. I'm following the directions here, and about a dozen other sites trying to describe the same thing.

Notes: