Drupal, subsites, and path-based URLs - php

Question

I'm working on trying to get a Drupal 9 site set up. The site was formerly a Drupal 7 multisite, but the developers working on it have broken it up into individual sites. So far, so good. However, they want to maintain the path-based URLs that were previously used, ie example.com/site1, example.com/site2, and so on (as opposed to site1.example.com). I've done this path-based config for multisites, so I assumed this wouldn't be much different, but I haven't had any luck getting Drupal to recognize that the other sites exist.
As best I've been able to figure out, I should be able to put the stand along site into the sites directory, configure sites.php to point to it, add the domain to the apache virtual hosts, and that should work (using the same .htaccess and settings.php as the multisites). I've also tried manipulating that configuration a few ways, with different results:
If I put the entire Drupal 9 site into a directory in sites, drush -l site1` gives me the db info for the default site and I get a 404 error
If I put on the web directory into sites, drush -l site1 gives me the db info for the default site and I get a 404 error
If I put the web directory in sites, but copy the settings.php to the sites/site1, drush -l site1 reports the db is connected, and I get a 500 http error
At this point, I'm running out of ideas as to what might be wrong - I haven't been working with Drupal for very long, and I'm not sure of better ways to troubleshoot. I've been able to confirm that the sites work as stand-alone sites, at least. Any ideas would be appreciated!
Here's the .htaccess:
#
# Apache/PHP/Drupal settings:
#
# Protect files and directories from prying eyes.
<FilesMatch "\.(engine|inc|install|make|module|profile|po|sh|.*sql|theme|twig|tpl(\.php)?|xtmpl|yml)(~|\.sw[op]|\.bak|\.orig|\.save)?$|^(\.(?!well-known).*|Entries.*|Repository|Root|Tag|Template|composer\.(json|lock)|web\.config)$|^#.*#$|\.php(~|\.sw[op]|\.bak|\.orig|\.save)$">
<IfModule mod_authz_core.c>
Require all denied
</IfModule>
<IfModule !mod_authz_core.c>
Order allow,deny
</IfModule>
</FilesMatch>
# Don't show directory listings for URLs which map to a directory.
Options -Indexes
# Set the default handler.
DirectoryIndex index.php index.html index.htm
# Add correct encoding for SVGZ.
AddType image/svg+xml svg svgz
AddEncoding gzip svgz
# Most of the following PHP settings cannot be changed at runtime. See
# sites/default/default.settings.php and
# Drupal\Core\DrupalKernel::bootEnvironment() for settings that can be
# changed at runtime.
# PHP 7, Apache 1 and 2.
<IfModule mod_php7.c>
php_value assert.active 0
</IfModule>
# PHP 8, Apache 1 and 2.
<IfModule mod_php.c>
php_value assert.active 0
</IfModule>
# Requires mod_expires to be enabled.
<IfModule mod_expires.c>
# Enable expirations.
ExpiresActive On
# Cache all files for 2 weeks after access (A).
ExpiresDefault A1209600
<FilesMatch \.php$>
# Do not allow PHP scripts to be cached unless they explicitly send cache
# headers themselves. Otherwise all scripts would have to overwrite the
# headers set by mod_expires if they want another caching behavior. This may
# fail if an error occurs early in the bootstrap process, and it may cause
# problems if a non-Drupal PHP file is installed in a subdirectory.
ExpiresActive Off
</FilesMatch>
</IfModule>
# Set a fallback resource if mod_rewrite is not enabled. This allows Drupal to
# work without clean URLs. This requires Apache version >= 2.2.16. If Drupal is
# not accessed by the top level URL (i.e.: http://example.com/drupal/ instead of
# http://example.com/), the path to index.php will need to be adjusted.
<IfModule !mod_rewrite.c>
FallbackResource /index.php
</IfModule>
# Various rewrite rules.
<IfModule mod_rewrite.c>
RewriteEngine on
# Set "protossl" to "s" if we were accessed via https://. This is used later
# if you enable "www." stripping or enforcement, in order to ensure that
# you don't bounce between http and https.
RewriteRule ^ - [E=protossl]
RewriteCond %{HTTPS} on
RewriteRule ^ - [E=protossl:s]
# Make sure Authorization HTTP header is available to PHP
# even when running as CGI or FastCGI.
RewriteRule ^ - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
# Block access to "hidden" directories whose names begin with a period. This
# includes directories used by version control systems such as Subversion or
# Git to store control files. Files whose names begin with a period, as well
# as the control files used by CVS, are protected by the FilesMatch directive
# above.
#
# NOTE: This only works when mod_rewrite is loaded. Without mod_rewrite, it is
# not possible to block access to entire directories from .htaccess because
# <DirectoryMatch> is not allowed here.
#
# If you do not have mod_rewrite installed, you should remove these
# directories from your webroot or otherwise protect them from being
# downloaded.
RewriteRule "/\.|^\.(?!well-known/)" - [F]
# If your site can be accessed both with and without the 'www.' prefix, you
# can use one of the following settings to redirect users to your preferred
# URL, either WITH or WITHOUT the 'www.' prefix. Choose ONLY one option:
#
# To redirect all users to access the site WITH the 'www.' prefix,
# (http://example.com/foo will be redirected to http://www.example.com/foo)
# uncomment the following:
# RewriteCond %{HTTP_HOST} .
# RewriteCond %{HTTP_HOST} !^www\. [NC]
# RewriteRule ^ http%{ENV:protossl}://www.%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
#
# To redirect all users to access the site WITHOUT the 'www.' prefix,
# (http://www.example.com/foo will be redirected to http://example.com/foo)
# uncomment the following:
# RewriteCond %{HTTP_HOST} ^www\.(.+)$ [NC]
# RewriteRule ^ http%{ENV:protossl}://%1%{REQUEST_URI} [L,R=301]
# Modify the RewriteBase if you are using Drupal in a subdirectory or in a
# VirtualDocumentRoot and the rewrite rules are not working properly.
# For example if your site is at http://example.com/drupal uncomment and
# modify the following line:
# RewriteBase /drupal
#
# If your site is running in a VirtualDocumentRoot at http://example.com/,
# uncomment the following line:
# RewriteBase /
# Redirect common PHP files to their new locations.
RewriteCond %{REQUEST_URI} ^(.*)?/(install\.php) [OR]
RewriteCond %{REQUEST_URI} ^(.*)?/(rebuild\.php)
RewriteCond %{REQUEST_URI} !core
RewriteRule ^ %1/core/%2 [L,QSA,R=301]
# Rewrite install.php during installation to see if mod_rewrite is working
RewriteRule ^core/install\.php core/install.php?rewrite=ok [QSA,L]
# Pass all requests not referring directly to files in the filesystem to
# index.php.
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} !=/favicon.ico
RewriteRule ^ index.php [L]
# For security reasons, deny access to other PHP files on public sites.
# Note: The following URI conditions are not anchored at the start (^),
# because Drupal may be located in a subdirectory. To further improve
# security, you can replace '!/' with '!^/'.
# Allow access to PHP files in /core (like authorize.php or install.php):
RewriteCond %{REQUEST_URI} !/core/[^/]*\.php$
# Allow access to test-specific PHP files:
RewriteCond %{REQUEST_URI} !/core/modules/system/tests/https?\.php
# Allow access to Statistics module's custom front controller.
# Copy and adapt this rule to directly execute PHP files in contributed or
# custom modules or to run another PHP application in the same directory.
RewriteCond %{REQUEST_URI} !/core/modules/statistics/statistics\.php$
# Deny access to any other PHP files that do not match the rules above.
# Specifically, disallow autoload.php from being served directly.
RewriteRule "^(.+/.*|autoload)\.php($|/)" - [F]
# Rules to correctly serve gzip compressed CSS and JS files.
# Requires both mod_rewrite and mod_headers to be enabled.
<IfModule mod_headers.c>
# Serve gzip compressed CSS files if they exist and the client accepts gzip.
RewriteCond %{HTTP:Accept-encoding} gzip
RewriteCond %{REQUEST_FILENAME}\.gz -s
RewriteRule ^(.*)\.css $1\.css\.gz [QSA]
# Serve gzip compressed JS files if they exist and the client accepts gzip.
RewriteCond %{HTTP:Accept-encoding} gzip
RewriteCond %{REQUEST_FILENAME}\.gz -s
RewriteRule ^(.*)\.js $1\.js\.gz [QSA]
# Serve correct content types, and prevent double compression.
RewriteRule \.css\.gz$ - [T=text/css,E=no-gzip:1,E=no-brotli:1]
RewriteRule \.js\.gz$ - [T=text/javascript,E=no-gzip:1,E=no-brotli:1]
<FilesMatch "(\.js\.gz|\.css\.gz)$">
# Serve correct encoding type.
Header set Content-Encoding gzip
# Force proxies to cache gzipped & non-gzipped css/js files separately.
Header append Vary Accept-Encoding
</FilesMatch>
</IfModule>
</IfModule>
# Various header fixes.
<IfModule mod_headers.c>
# Disable content sniffing, since it's an attack vector.
Header always set X-Content-Type-Options nosniff
# Disable Proxy header, since it's an attack vector.
RequestHeader unset Proxy
</IfModule>