Pre-compressed (gzip) HTML using fastcgi_cache?

[seo010]

Hi!

I was wondering if anyone has an idea to serve pre-compressed (gzip) HTML
using proxy_cache / fastcgi_cache.

I tried a solution with a map of http_accept_encoding as part of the
fastcgi_cache_key with gzip compressed output from the script, but it
resulted into strange behavior (the MD5 hash for the first request
corresponds to the KEY, the next requests with an unknown MD5 hash using the
same KEY.

Nginx version: 1.11.1

The initial solution to serve pre-compressed gzip HTML from proxy_cache /
fastcgi_cache was the following:

Map:
map $http_accept_encoding $gzip_enabled {
    ~*gzip                gzip;
}

Server:
fastcgi_cache_path /path/to/cache/nginx levels=1:2 keys_zone=XXX:20m
max_size=4g inactive=7d;

PHP-FPM proxy:
set $cache_key "$gzip_enabled$request_method$request_uri";

fastcgi_pass unix:/path/to/php-fpm.sock;
fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
fastcgi_param PHP_VALUE "error_log=/path/to/logs/php.error.log";
fastcgi_intercept_errors on;

# full page cache
fastcgi_no_cache $skip_cache_save;
fastcgi_cache_bypass $skip_cache;
fastcgi_cache XXX;
fastcgi_cache_use_stale error timeout invalid_header updating http_500;
fastcgi_ignore_headers Cache-Control Expires Set-Cookie;
fastcgi_cache_valid 200 7d; # valid for 7 days
fastcgi_cache_valid 301 302 304 1h;
fastcgi_cache_valid any 5m;
fastcgi_cache_lock on;
fastcgi_cache_lock_timeout 5s;
fastcgi_cache_key $cache_key;

add_header X-Cache $upstream_cache_status;
#add_header X-Cache-Key $cache_key;

include fastcgi_params;

It did work when testing in 1 browser: it showed "MISS" and "HIT" for 2
requests. The cache directory showed the correct MD5 hash for the key.

But when testing the same URL again in a different browser, a yet
unexplained behavior occurred. A totally new MD5 hash was used to store the
same pre-compressed content. When viewing the cached file, the exact same
KEY was shown (without additional spaces or special characters).

Although the solution with a GZIP parameter may work, I was wondering if
anyone knows of a better solution to serve pre-compressed HTML from Nginx
cache as it results into 4 to 10ms latency saving per request on a idle
quad-core server with 4x SSD in RAID 10.

I could not find any information related to a solution in Google while it
appears to be a major potential for performance gain on high traffic
websites.

Best Regards,
Jan Jaap

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,270604,270604#msg-270604