Assume there are 5 second-level domain names:

aaa.example.com
bbb.example.com
ccc.example.com
ddd.example.com
eee.example.com

When configuring nginx, the server module looks like this:

server {
    listen 443 ssl http2;
    
    server_name  aaa.example.com;
    
    root   /var/www/aaa.example.com/public;
    index  index.php index.html index.htm;
    
    location / {
        root   /var/www/aaa.example.com/public;
        try_files $uri $uri/ /index.php?$query_string;
        index  index.php index.html index.htm;
    }


    location ~ \.php$ {
        try_files $uri /index.php =404;
        fastcgi_split_path_info ^(.+\.php)(/.+)$;
        fastcgi_pass   unix:/dev/shm/php-fpm.sock;
        fastcgi_index  index.php;
        fastcgi_param  SCRIPT_FILENAME  $document_root$fastcgi_script_name;
        include        fastcgi_params;
    }
    
    #...
    #...
    #...
}

Question:
1. There are 5 second-level domain names. Do I need to write 5 server modules? Can I write a general-purpose server module that only uses one?

2. If you write 5 server modules, the location ~ \.php${ } modules in each server module are the same. This location ~ \.php${ } Can a module be written only once and shared? That is, can it be moved to the http module, the upper module of the server module?

3. In many examples, the root and index must be written twice, once in the server, and again in the next layer's location / { } module. Why is this?