The if block should ideally be employed for simple situations, as its behavior might be surprising in some cases. Apart from the fact that if statements cannot be nested, the following situations may present issues:

# Two consecutive statements with the same condition: 
location / { 
    if ($uri = "/test.html") { 
       add_header X-Test-1 1; 
       expires 7; 
    } 
    if ($uri = "/test.html") { 
       add_header X-Test-1 1; 
    } 
} 

In this case, the first if block is ignored and only the second one is processed. However, if you insert a Rewrite module directive in the first block, such as rewrite, break, or return, the first block will be processed and the second one will be ignored.

There are many other cases where the use of if causes problems:

• Having try_files and if statements in the same location block is not recommended, as the try_files directive will, in most cases, be ignored.
• Some directives are theoretically allowed within the if block, but can create serious issues; for instance, proxy_pass and fastcgi_pass. You should keep those within location blocks.
• You should avoid using if blocks within a location block that captures regular expression patterns from within its modifier.

These issues originate from the fact that while the Nginx configuration is written in what appears to be a declarative language, directives from the Rewrite module, such as if, rewrite, return, or break, make it look like event-based programming. In general, you should try to avoid using directives from other modules within if blocks as much as possible.