Only certain environment variables are set in systemd

Times change and so do best practices.

The current best way to do this is to run systemctl edit myservice, which will create an override file for you or let you edit an existing one.

In normal installations this will create a directory /etc/systemd/system/myservice.service.d, and inside that directory create a file whose name ends in .conf (typically, override.conf), and in this file you can add to or override any part of the unit shipped by the distribution.

For instance, in a file /etc/systemd/system/myservice.service.d/myenv.conf:

[Service]
Environment="SECRET=pGNqduRFkB4K9C2vijOmUDa2kPtUhArN"
Environment="ANOTHER_SECRET=JP8YLOc2bsNlrGuD6LVTq7L36obpjzxd"

Also note that if the directory exists and is empty, your service will be disabled! If you don't intend to put something in the directory, ensure that it does not exist.

For reference, the old way was:

The recommended way to do this is to create a file /etc/sysconfig/myservice which contains your variables, and then load them with EnvironmentFile.

For complete details, see Fedora's documentation on how to write a systemd script.

I agree with what Tvon says and would like to add more specifically that systemd would really be the wrong place to put those Apache environment variables. Other applications or processes that use Systemd have no need to know about those variables.

I would also consider whether you would be hosting multiple PHP sites on the same server and if so rather than sticking everything in

/etc/httpd/conf.d/vhosts.conf

I would also consider using the site-available method aka the "debian-way"

How to configure Apache (sites-available vs httpd.conf)

Below method based on this guide for Centos https://www.digitalocean.com/community/tutorials/how-to-set-up-apache-virtual-hosts-on-centos-7#step-four-%E2%80%94-create-new-virtual-host-files

sudo mkdir /etc/httpd/sites-available
sudo mkdir /etc/httpd/sites-enabled

Tell Apache to look for virtual hosts in the sites-enabled directory. by editing Apache's main config file and add a line declaring an optional directory for additional configuration files:

sudo nano /etc/httpd/conf/httpd.conf

Add a line to end of file IncludeOptional sites-enabled/*.conf

Save and close the file. Then create a virtual host file.

sudo nano /etc/httpd/sites-available/example.com.conf

<VirtualHost *:80>

</VirtualHost>

Then add the directvies for your first website

<VirtualHost *:80>
    ServerName www.example.com
    ServerAlias example.com

    SetEnv API_USERNAME 'my_special_username'
    SetEnv API_PASSWORD 'my_special_password'

    DocumentRoot /var/www/example.com/public_html
    ErrorLog /var/www/example.com/error.log
    CustomLog /var/www/example.com/requests.log combined

</VirtualHost>

Save and close the file. Then make a copy called example2.com.conf for your second website

sudo cp /etc/httpd/sites-available/example.com.conf /etc/httpd/sites-available/example2.com.conf

Edit the file and make relevant changes

sudo nano /etc/httpd/sites-available/example2.com.conf

<VirtualHost *:80>
    ServerName www.example2.com
    ServerAlias example2.com

    SetEnv API_USERNAME 'my_other_special_username'
    SetEnv API_PASSWORD 'my_other_special_password'

    DocumentRoot /var/www/example2.com/public_html
    ErrorLog /var/www/example2.com/error.log
    CustomLog /var/www/example2.com/requests.log combined

</VirtualHost>

You will then need to enable the sites by creating a symlink from the sites-enabled directory to the sites-available directory

sudo ln -s /etc/httpd/sites-available/example.com.conf /etc/httpd/sites-enabled/example.com.conf
sudo ln -s /etc/httpd/sites-available/example2.com.conf /etc/httpd/sites-enabled/example2.com.conf

Then restart apache (usually I do a configtest first to see if any errors)

sudo apachectl configtest

if all okay

sudo apachectl restart

Other benefits of this method is you could create new versions of existing configs and use symlink to point back and forth if any issues with new config or enable/disable websites when necessary.