In some situations, if not most, you should avoid using if blocks. There are two main issues occurring, regardless of the Nginx build you are using.
There are some cases where if is used inappropriately, in a way that risks saturating your storage device with useless checks:
location / {
# Redirect to index.php if the requested file is not found
if (!-e $request_filename) {
rewrite ^ index.php last;
}
}With such a configuration, every single request received by Nginx will trigger a complete verification of the directory tree for the requested filename, thus requiring multiple storage disk access system calls. If you test /usr/local/nginx/html/hello.html, Nginx will check /, /usr, /usr/local, /usr/local/nginx, and so on. In any case, you should avoid resorting to such a statement. For example, by filtering the file type beforehand (for instance, by making such a check, only if the requested file matches specific extensions):
location / {
# Filter file extension first
if ($request_filename !~ "\.(gif|jpg|jpeg|png)" {
break;
}
if (!-f $request_filename) {
rewrite ^ index.php last;
}
}The if block should ideally be employed for simple situations, as its behavior might be surprising in some cases. Apart from the fact that if statements cannot be nested, the following situations may present issues:
# Two consecutive statements with the same condition:
location / {
if ($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 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_filesandifstatements in the same location block is not recommended as thetry_filesdirective will, in most cases, be ignored.Some directives are theoretically allowed within the
ifblock but can create serious issues, for instance,proxy_passandfastcgi_pass. You should keep those withinlocationblocks.You should avoid using
ifblocks within alocationblock that captures regular expression patterns from its modifier.
The origin of these problems comes from the fact that while the Nginx configuration is established in a declarative language, directives from the Rewrite module such as if, rewrite, return, or break make it look like actual scripting. In general, you should try to avoid using directives from other modules within if blocks as much as possible.