Directives are brought in by modules; if you activate a new module, a specific set of directives become available. Modules may also enable directive blocks, which allow for a logical construction of the configuration:

events { 
    worker_connections 1024; 
} 

The events block that you can find in the default configuration file is brought in by the events module. The directives that the module enables can only be used within that block. In the preceding example, worker_connections will only make sense in the context of the events block. On the other hand, some directives must be placed at the root of the configuration file because they have a global effect on the server. The root of the configuration file is also known as the main block.

For the most part, blocks can be nested into each other, following a specific logic. The following sequence demonstrates the structure of a simple website setup, making use of nested blocks:

http { 
    server { 
        listen 80; 
        server_name example.com; 
        access_log /var/log/nginx/example.com.log; 
        location ^~ /admin/ { 
            index index.php; 
       } 
    } 
} 

The topmost directive block is the http block, in which you may declare a variety of configuration directives, as well as one or more server blocks. A server block allows you to configure a virtual host, in other words, a website that is to be hosted on your machine. The server block, in this example, contains some configuration that applies to all HTTP requests with a Host header exactly matching example.com.

Within this server block, you may insert one or more location blocks. These allow you to enable settings only when the requested URI matches the specified path. More information is provided in the The Location block section of Chapter 3, HTTP Configuration.

Last but not least, configuration is inherited within children blocks. The access_log directive (defined at the server block level in this example) specifies that all HTTP requests for this server should be logged into a text file. This is still true within the location child block, although you have the possibility of disabling it by reusing the access_log directive:

[...] 
    location ^~ /admin/ { 
        index index.php; 
        access_log off; 
    } 
[...] 

In this case, logging will be enabled everywhere on the website, except for the /admin/ location path. The value set for the access_log directive at the server block level is overridden by the one at the location block level.