Overview of the process:
Step 1: Instantiate the master site
In this example, we install Drupal with the following steps:
1.1: Create a database for the multisite root site, ex: d8multisite.
1.2: Download and extract a copy of Drupal 8 into your web directory.
1.3: Create an Apache virtual host for the root site. Read up on virtual host configuration. An example virtual host config:
<VirtualHost *:80>
# virtual host configuration for for drupal 8 multisite root site
ServerAdmin me@domain.com
DocumentRoot /var/www/d8multisite
ServerName d8multisite.com
ServerAlias www.d8multisite.com
<Directory />
Options FollowSymLinks
AllowOverride None
</Directory>
<Directory /var/www/d8multisite>
Options Indexes FollowSymLinks MultiViews
AllowOverride All
Order allow,deny
Allow from all
</Directory>
ErrorLog ${APACHE_LOG_DIR}/d8multisite_error.log
LogLevel warn
CustomLog ${APACHE_LOG_DIR}/d8multisite_access.log combined
</VirtualHost>
1.4: Install Drupal by visiting d8multisite.com and following the install UI.
Step 2: Configure the first site for the multisite
Now that we have the root site set up, can begin configuring our first site called site1. Here are the steps in this process:
2.1: Create a folder for site1 in your multisite: /d8multisite/sites/site1.d8multisite.com
2.1: Create a database for site1, ex: d8multisite-site1
2.3: Make a copy of /d8multisite/sites/example.sites.php called /d8multisite/sites/sites.php
2.4: Edit sites.php so the end of the file looks like this:
# make the root drupal site aware of site1:
$sites['site1.d8multisite.com'] = 'site1.d8multisite.com';
2.5: Create an Apache virtual host for site1. Note that this virtual host should point to the root site, not the site's subdirectory. Also note that you can also forego creating a new virtual host configuration for this site and just the new site as a ServerAlias to the root site. In this example, we will, however, create a separate virtual host for site1:
<VirtualHost *:80>
ServerAdmin me@domain.com
DocumentRoot /var/www/d8multisite
ServerName site1.d8multisite.com
<Directory />
Options FollowSymLinks
AllowOverride None
</Directory>
<Directory /var/www/d8multisite>
Options Indexes FollowSymLinks MultiViews
AllowOverride All
Order allow,deny
Allow from all
</Directory>
ErrorLog ${APACHE_LOG_DIR}/site1-d8multisite_error.log
LogLevel warn
CustomLog ${APACHE_LOG_DIR}/site1-d8multisite_error.log combined
</VirtualHost>
2.6: Copy /d8multisite/sites/default/default.settings.php to the new site's directory as settings.php:
#from the drupal root folder
cp sites/default/default.settings.php sites/site1.d8multisite.com/settings.php
2.7: Finish the Drupal installation process for site1 by visiting the site's domain.
You can repeat these steps each time you want to build a site in your multisite. You can also use domains like example.com and site1.anotherdomain.com. More details on domains, URLs, and sites subdirectory names.
Step 3: Enable per-site modules
In some cases, you may want one of your sites within your multisite to have its own modules. To enable this, you simply need to create the appropriate folders within the target site’s folder. In this example, we will enable site1 to have its own modules:
Note: The assumption here is that you can do this with themes, libraries, and files. More testing and documentation is needed here.