Wordpress Suspected bug with Redis Caching when Accept-Encoding is "gzip, deflate, br"

This is a VERY peculiar issue which took me forever to figure out...

CentOS Linux release 7.9.2009 (Core)
Centmin Mod version: 130.00beta01
nginx version: nginx/1.25.3 (091123-121301-centos7-kvm-48ad4d7)
WordPress installed with option 2: Redis Nginx Level Caching
nginx helper plugin configured and working correctly.

I have Cloudflare in front of my website with the proxy enabled (but no APO, caching rules etc.)

Everything works perfectly fine with the caching config when I access the website via Cloudflare.

---

Redis cache keys look like:

Code:

1707585329.721277 [0 127.0.0.1:41916] "get" "nginx-cache:httpsGETwww.mydomain.com/mypage/gzip"

and X-Cache: returns a HIT for $srcache_fetch_status as expected.

I had to briefly set a host header in /etc/hosts on my local workstation to bypass Cloudflare to do some testing before I moved the site from one server to another, when I noticed that X-Cache: persistently returned a MISS status which I thought was unusual.

Running redis-cli->MONITOR I then noticed that the cache key was storing a different value for http_accept_encoding as follows:

Code:

1707585546.242559 [0 127.0.0.1:41916] "get" "nginx-cache:httpsGETwww.mydomain.com/mypage/gzip,%20deflate,%"

this then triggered a srcache_store event with the following key:

Code:

1707585546.942840 [0 127.0.0.1:41916] "set" "nginx-cache:httpsGETwww.mydomain.com/mypage/gzip, deflate, br"

Note the difference in the values for http_accept_encoding ?

I wonder is this due to the differences in how the keys are set when there are multiple accepted encoding values?

Code:

   
srcache_fetch GET /redis-fetch $key;
srcache_store PUT /redis-store key=$escaped_key;

CloudFlare seems to only send "gzip" as the Accept-Encoding value, whereas when I bypass Cloudflare completey, Chrome is sending "gzip, deflate, br" as the Accept-Encoding value.

 

it's always a miss.
likely because of the difference in set/get rules

if you look again the SET rule ends with "gzip,%20deflate," and GET rule ends with "gzip, deflate, br"

 

@eva2000 you are an absolute legend!
that works perfectly!
thanks so much for solving that so quickly AND on a weekend.
do you ever sleep?

 

Yes correct.

No - I didn't follow the steps to enable Brotli compression, but... interestingly, checking this on my 2 most recent Centmin Mod machines, looks like Brotli is in place on the AlmaxLinux version.

Machine 1:
AlmaLinux release 8.9 (Midnight Oncilla)
Centmin Mod 130.00beta01

Brotli looks to be in place

Code:

nginx version: nginx/1.25.3 (140124-161036-almalinux8-kvm-a6feed4-br-a71f931)
built with OpenSSL 3.1.4 24 Oct 2023
TLS SNI support enabled
configure arguments: --with-ld-opt='-Wl,-E -L/usr/local/zlib-cf/lib -L/usr/local/nginx-dep/lib -lpcre2-8 -ljemalloc -Wl,-z,relro,-z,now -Wl,-rpath,/usr/local/nginx-dep/lib:/usr/local/zlib-cf/lib:/usr/local/nginx-dep/lib -pie -B/usr/local/libexec/mold' --with-cc-opt='-I/usr/local/zlib-cf/include -I/usr/local/nginx-dep/include -m64 -march=x86-64-v3 -mavx -mavx2 -mpclmul -msse4 -msse4.1 -msse4.2 -fPIC -g -O3 -Wno-strict-aliasing -fstack-protector-strong -B/usr/local/libexec/mold --param=ssp-buffer-size=4 -Wformat -Werror=format-security -Wno-pointer-sign -Wimplicit-fallthrough=0 -Wno-implicit-function-declaration -Wno-int-conversion -Wno-error=unused-result -Wno-unused-result -Wno-error=vla-parameter -fcode-hoisting -Wno-cast-function-type -Wno-format-extra-args -Wp,-D_FORTIFY_SOURCE=2' --prefix=/usr/local/nginx --sbin-path=/usr/local/sbin/nginx --conf-path=/usr/local/nginx/conf/nginx.conf --build=140124-161036-almalinux8-kvm-a6feed4-br-a71f931 --with-compat --with-http_stub_status_module --with-http_secure_link_module --with-http_flv_module --with-http_mp4_module --add-module=../nginx-rtmp-module --with-libatomic --with-http_gzip_static_module --add-dynamic-module=../ngx_brotli --add-dynamic-module=../ngx_http_geoip2_module --with-http_sub_module --with-http_addition_module --with-http_image_filter_module=dynamic --with-http_geoip_module --add-dynamic-module=../njs/nginx --with-stream_geoip_module --with-stream_realip_module --with-stream_ssl_preread_module --with-threads --with-stream --with-stream_ssl_module --with-http_slice_module --with-http_realip_module --add-dynamic-module=../ngx-fancyindex-0.4.2 --add-module=../ngx_cache_purge-2.5.1 --add-dynamic-module=../ngx_devel_kit-0.3.2 --add-dynamic-module=../set-misc-nginx-module-0.33 --add-dynamic-module=../echo-nginx-module-0.63 --add-module=../redis2-nginx-module-0.15 --add-module=../ngx_http_redis-0.4.0-cmm --add-module=../memc-nginx-module-0.19 --add-module=../srcache-nginx-module-0.33 --add-dynamic-module=../headers-more-nginx-module-0.34 --with-pcre-jit --with-zlib=../zlib-cloudflare-1.3.3 --with-zlib-opt=-fPIC --with-http_ssl_module --with-http_v2_module --with-openssl=../openssl-3.1.4 --with-openssl-opt='enable-ec_nistp_64_gcc_128 enable-tls1_3 -fuse-ld=gold'

Machine 2:
CentOS Linux release 7.9.2009 (Core)
Centmin Mod 130.00beta01

Code:

nginx version: nginx/1.25.3 (091123-121301-centos7-kvm-48ad4d7)
built by gcc 10.2.1 20210130 (Red Hat 10.2.1-11) (GCC)
built with OpenSSL 1.1.1w  11 Sep 2023
TLS SNI support enabled
configure arguments: --with-ld-opt='-Wl,-E -L/usr/local/zlib-cf/lib -L/usr/local/nginx-dep/lib -ljemalloc -Wl,-z,relro -Wl,-rpath,/usr/local/zlib-cf/lib:/usr/local/nginx-dep/lib -flto=4 -fuse-ld=gold' --with-cc-opt='-I/usr/local/zlib-cf/include -I/usr/local/nginx-dep/include -m64 -march=x86-64 -g -O3 -fstack-protector-strong -flto=4 -fuse-ld=gold --param=ssp-buffer-size=4 -Wformat -Werror=format-security -Wno-pointer-sign -Wimplicit-fallthrough=0 -Wno-missing-profile -Wno-implicit-function-declaration -Wno-int-conversion -Wno-unused-result -Wno-unused-result -Wno-stringop-overflow -fcode-hoisting -Wno-cast-function-type -Wno-format-extra-args -Wno-vla-parameter -Wno-stringop-overflow -Wp,-D_FORTIFY_SOURCE=2' --sbin-path=/usr/local/sbin/nginx --conf-path=/usr/local/nginx/conf/nginx.conf --build=091123-121301-centos7-kvm-48ad4d7 --with-compat --without-pcre2 --with-http_stub_status_module --with-http_secure_link_module --with-libatomic --with-http_gzip_static_module --with-http_sub_module --with-http_addition_module --with-http_image_filter_module=dynamic --with-http_geoip_module --with-stream_geoip_module --with-stream_realip_module --with-stream_ssl_preread_module --with-threads --with-stream --with-stream_ssl_module --with-http_realip_module --add-dynamic-module=../ngx-fancyindex-0.4.2 --add-module=../ngx_cache_purge-2.5.1 --add-dynamic-module=../ngx_devel_kit-0.3.2 --add-dynamic-module=../set-misc-nginx-module-0.33 --add-dynamic-module=../echo-nginx-module-0.63 --add-module=../redis2-nginx-module-0.15 --add-module=../ngx_http_redis-0.4.0-cmm --add-module=../memc-nginx-module-0.19 --add-module=../srcache-nginx-module-0.33 --add-dynamic-module=../headers-more-nginx-module-0.34 --with-pcre-jit --with-zlib=../zlib-cloudflare-1.3.3 --with-http_ssl_module --with-http_v2_module --with-openssl=../openssl-1.1.1w --with-openssl-opt='enable-ec_nistp_64_gcc_128 enable-tls1_3 -fuse-ld=gold'

Chrome 121.0.6167.85 (macOS 14.2.1)

 

Ah yip I did indeed use the EL8+ edge installer

Fantastic! Will let you know if I spot any other side effects. thanks again!