Comment 5 for bug 1865218

The fix for 1850933 is only handling 7.2->7.4 and 7.3->7.4 upgrades. Presumably a similar fix could be done for other upgrade paths to 7.4, but an SRU would probably be needed for 7.0->7.2 upgrades.

However, the more pressing issue would be why the 7.2->7.4 upgrade done in comment #2 did not work as intended by the fix.

I'm reproducing a failure using clean lxc:

Preparing to unpack .../25-apache2-bin_2.4.41-4ubuntu2_amd64.deb ...
Unpacking apache2-bin (2.4.41-4ubuntu2) over (2.4.29-1ubuntu4.13) ...
Preparing to unpack .../26-libapache2-mod-php_2%3a7.4+75_all.deb ...
Unpacking libapache2-mod-php (2:7.4+75) over (1:7.2+60ubuntu1) ...
(Reading database ... 32550 files and directories currently installed.)
Removing libapache2-mod-php7.2 (7.2.24-0ubuntu0.18.04.3) ...
Package apache2 is not configured yet. Will defer actions by package libapache2-mod-php7.2.
Selecting previously unselected package libapache2-mod-php7.4.
(Reading database ... 32543 files and directories currently installed.)
Preparing to unpack .../libapache2-mod-php7.4_7.4.3-4ubuntu1_amd64.deb ...
Unpacking libapache2-mod-php7.4 (7.4.3-4ubuntu1) ...

...
Setting up libapache2-mod-php7.4 (7.4.3-4ubuntu1) ...
Package apache2 is not configured yet. Will defer actions by package libapache2-mod-php7.4.

Creating config file /etc/php/7.4/apache2/php.ini with new version
libapache2-mod-php7.4: php7.2 module already enabled, not enabling PHP 7.4
Setting up packagekit-tools (1.1.13-2ubuntu1) ...
Setting up apache2 (2.4.41-4ubuntu2) ...
Job for apache2.service failed because the control process exited with error code.
See "systemctl status apache2.service" and "journalctl -xe" for details.
invoke-rc.d: initscript apache2, action "restart" failed.
● apache2.service - The Apache HTTP Server
     Loaded: loaded (/lib/systemd/system/apache2.service; enabled; vendor preset: enabled)
     Active: failed (Result: exit-code) since Tue 2020-04-14 18:16:42 UTC; 4ms ago
       Docs: https://httpd.apache.org/docs/2.4/
    Process: 56492 ExecStart=/usr/sbin/apachectl start (code=exited, status=1/FAILURE)

Apr 14 18:16:42 php-fix-lp1865218-mod-php-upgrade systemd[1]: Starting The Apache HTTP Server...
Apr 14 18:16:42 php-fix-lp1865218-mod-php-upgrade apachectl[56496]: apache2: Syntax error on line 146 of /etc/apache2
/apache2.conf: Syntax error on line 3 of /etc/apache2/mods-enabled/php7.2.load: Cannot load /usr/lib/apache2/modules/
libphp7.2.so into server: /usr/lib/apache2/modules/libphp7.2.so: cannot open shared object file: No such file or dire
ctory
Apr 14 18:16:42 php-fix-lp1865218-mod-php-upgrade apachectl[56492]: Action 'start' failed.
Apr 14 18:16:42 php-fix-lp1865218-mod-php-upgrade apachectl[56492]: The Apache error log may have more information.
Apr 14 18:16:42 php-fix-lp1865218-mod-php-upgrade systemd[1]: apache2.service: Control process exited, code=exited, s
tatus=1/FAILURE
Apr 14 18:16:42 php-fix-lp1865218-mod-php-upgrade systemd[1]: apache2.service: Failed with result 'exit-code'.
Apr 14 18:16:42 php-fix-lp1865218-mod-php-upgrade systemd[1]: Failed to start The Apache HTTP Server.
invoke-rc.d: release upgrade in progress, error is not fatal
Setting up fwupd-signed (1.27+1.3.9-4) ...
Setting up software-properties-common (0.98.7) ...
Setting up libapache2-mod-php (2:7.4+75) ...
...
Setting up ubuntu-server (1.447) ...
Processing triggers for php7.4-cli (7.4.3-4ubuntu1) ...
Processing triggers for dbus (1.12.16-2ubuntu2) ...
Processing triggers for libapache2-mod-php7.4 (7.4.3-4ubuntu1) ...
...

Purging configuration files for php7.2-common (7.2.24-0ubuntu0.18.04.3) ...
dpkg: warning: while removing php7.2-common, directory '/etc/php/7.2/mods-available' not empty so not removed
Purging configuration files for php7.2-opcache (7.2.24-0ubuntu0.18.04.3) ...
Purging configuration files for php7.2-cli (7.2.24-0ubuntu0.18.04.3) ...
dpkg: warning: while removing php7.2-cli, directory '/etc/php/7.2/cli/conf.d' not empty so not removed

# ls /etc/apache2/mods-enabled/php*
/etc/apache2/mods-enabled/php7.2.conf /etc/apache2/mods-enabled/php7.2.load