White screen when not logged in

Question

We have two servers running identical instances of an EE 5.2.4, using PHP 7.x via IIS. Our production machine works fine, no issues. Our backup server is the issue.

On the backup server: I can log into CP with no issues, and once logged in, I can view the site and all's well. If I'm not logged in / authenticated, I get the white screen of death. I've enabled debugging, and set $debug = 2 in index.php, so that everyone can see any errors (nothing shown), checked all debug options in CP, I've checked PHP logs, MySql logs, Event Viewer, everything I can think of. No errors are shown. Today I started commenting out template sections out of desperation, with no luck.

Clearly, something is different between the two servers. Is there anything obvious that I'm overlooking that would be bypassed when an admin is logged in, while viewing the site that would trigger for a non-authenticated user? Has anyone else dealt with this issue?

Answer 1

After digging as deeply as I knew how, I eventually took a backup sql script of the production and backup databases, along with the site files from both servers and used WinMerge to compare both. I found entries in the table "exp_template_no_access" in the backup server db, but not in production.

Those entries lead me to discover that there were no permissions assigned to a particular template used throughout the site, only on the backup server. We're unsure if someone mis-clicked or if this can occur when/if someone updates the physical template file rather than going through the EE admin dashboard. You can find this by accessing the template, then the "Access" tab.

Rather than displaying "Access Denied", or perhaps something similar like "You don't have access to this template", EE just shows the infamous White Screen of Death. No errors, no helpful tips to help me dig through the myriad of settings to track this down, in spite of error settings being turned on. I couldn't get a template access notification. Perhaps I missed something in my debug efforts. Fun times.

Thanks to @jphansen and @jrothafer for all of your help! Hopefully this answer will help someone else if they run into a similar issue.

Answer 2

Thanks for the earlier answer, this just expands on it slightly. I had the same issue which also had me tearing my hair out for a while with the unhelpful White Screen of Death.

This is looking like an EE issue that arises when restoring a backed-up database. In this case, the database was migrated from one functioning v5.3.0 installation (PHPv7.1 / CentOS6) to an upgraded server (PHPv7.3.16 / CentOS7).

As described, the exp_template_no_access table in the destination db displayed entries not found in the source db:

This is displayed in the Control Panel as unchecked Allowed member groups entries:

Once re-checked, the frontend pages appear again.

We're unsure if someone mis-clicked or if this can occur when/if someone updates the physical template file rather than going through the EE admin...

In this case the only update made to this template was to the code in the browser Control Panel entry (the EE admin). The non-logged-in view may have already been broken, or broke immediately after the template update - it wasn't being monitored. Because this template was the default master layout for the site, all pages appeared blank except to a Super Admin.

Other templates updated in the same way subsequently did not seem to have their Access permissions altered. This may suggest a one-off issue manifesting after restoration of the database.

A quick test Export of the source db and then Import into a new db (using PHPMyAdmin on the same CentOS6 server) did not show any population of the exp_template_no_access table.