How can I check that the nginx gzip_static module is working?

How can I check that nginx is serving the .gz version of static files, if they exist?

I compiled nginx with the gzip static module, but I don't see any mention of the .gz version being served in my log开发者_开发问答s. (I have minified global.js and global.css files with .gz versions of them in the same directory).

The relevant part of nginx.conf looks like this:

gzip  on;
gzip_static on;
gzip_http_version 1.0;
gzip_disable "MSIE [1-6]\.";
gzip_vary on;

gzip_comp_level 2;
gzip_proxied any;
gzip_types text/plain text/html text/css application/x-javascript text/xml application/xml application/xml+rss text/javascript;

Any pointers would be appreciated.

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Use strace. First, you need to detect PID of nginx process:

# ps ax | grep nginx
25043 ?        Ss     0:00 nginx: master process /usr/sbin/nginx -c /etc/nginx/nginx.conf
25044 ?        S      0:02 nginx: worker process

Ok, so 25044 is the worker process. Now, we trace it:

# strace -p 25044 2>&1 | grep gz
open("/var/www/css/ymax.css.gz", O_RDONLY|O_NONBLOCK) = 438
open("/var/www/css/patches/patch_my_layout.css.gz", O_RDONLY|O_NONBLOCK) = -1 ENOENT (No such file or directory)
open("/var/www/yaml/core/iehacks.css.gz", O_RDONLY|O_NONBLOCK) = -1 ENOENT (No such file or directory)
open("/var/www/js/koznazna5.js.gz", O_RDONLY|O_NONBLOCK) = -1 ENOENT (No such file or directory)
open("/var/www/css/ymax.css.gz", O_RDONLY|O_NONBLOCK) = 216

As you can see, it is trying to find .gz versions of files.

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Change the content of the non-gzipped file. And then touch both files (simultaneously—that is: in the same instantiation of touch). If when you load the file in an browser (cache-wiped) you get the non-changed file, then nginx served the static-cached-gzipped file.

An easy way to avoid “did I just fetch the cache?” worries is to fetch from the command-line with curl since curl doesn’t cache.

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I would disable automatic compression and log gzip_ratio:

http {
   gzip off;
   gzip_static on;

   log_format log_with_ratio "... $gzip_ratio ...";

   server {
      access_log /var/log/nginx/file.log log_with_ratio;
   }
}

Note, that you may override gzip, gzip_static and access_log per server and location levels.

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There is some hint I've noticed regarding ETag response header.

If static file is served by nginx, then header looks like this: ETag: "135a-BQhu6KL71dyeCXcVZme6ug", however, when nginx is compressing the response (through gzip module) it looks like this: ETag: W/"135a-BQhu6KL71dyeCXcVZme6ug" (notice W/).

You can use this as well as Content-Encoding: gzip to distinguish plain static files, pre-compressed static files, and files compressed on the fly.

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I usually use Chrome Dev tools and look at the file sizes for the files in question.

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You can use Chrome Dev Tools via the Network tab if you enable the Content-Encoding column (right-click on the columns to enable/disable specific content in the table):

Chrome Dev Tools with Content-Encoding column enabled screenshot