# Change blank uwsgi\_cache\_key default, or log warning **URL:** \ **Category:** NGINX\ **Created:** [September 9, 2014, 8:25pm UTC](https://www.ruby-forum.com/t/change-blank-uwsgi-cache-key-default-or-log-warning/231957 "2014-09-09T20:25:44Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\ **Post date:** [September 9, 2014, 8:25pm UTC](https://www.ruby-forum.com/t/change-blank-uwsgi-cache-key-default-or-log-warning/231957/1 "2014-09-09T20:25:44Z")
Hello, Because uwsgi\_cache\_key has no default value (or rather, has the empty string as its default value), a configuration with uwsgi\_cache set but uwsgi\_cache\_key not set behaves in a way that is very unlikely to be desired: Nginx caches the first publicly cacheable response it gets from upstream (for any request), and serves that cached response to _any_ request mapping to the same location. The internals of that can be seen in the debug log, where the cache key is empty for all requests: 2014/09/09 17:41:02 [debug] 91211#0: \*13 http cache key: “” This is in contrast to a configuration with proxy\_cache enabled but proxy\_cache\_key not set; that behaves OK because proxy\_cache\_key has a useful default. Because of the _general_ correspondence between the http\_proxy and http\_uwsgi modules, it’s easy to fall into this trap, defining uwsgi\_cache but not uwsgi\_cache\_key. When that happens, and unexpected responses start coming back, the first place one looks is error.log, and there’s nothing there. To get rid of this gotcha, I suggest either: 1. log a warning whenever a location/server/http block has uwsgi\_cache set but no uwsgi\_cache\_key set. or 1. change the default value of uwsgi\_cache\_key to a more useful default, such as $scheme$host$request\_uri, similar to proxy\_cache\_key (not quite the same, because the proxy\_cache\_key has $proxy\_host in its default, and there is no corresponding $uwsgi\_host). You might not want to make such a default-behavior change in a subminor release — but as a counterargument, the current default seems quite unlikely to be relied on by anyone. Cheers, Gulli Posted at Nginx Forum: > **[Change blank uwsgi\_cache\_key default, or log warning](https://forum.nginx.org/read.php?2,253149,253149#msg-253149)** > > Hello, Because uwsgi\_cache\_key has no default value (or rather, has the empty string as its default value), a configuration with uwsgi\_cache set but uwsgi\_cache\_key not set behaves in a way that is very unlikely to be desired: Nginx caches the first... ---
**Author:** ![gthb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/cc9497/32.png) [@gthb](https://www.ruby-forum.com/u/gthb)\ **Post date:** [September 10, 2014, 7:49pm UTC](https://www.ruby-forum.com/t/change-blank-uwsgi-cache-key-default-or-log-warning/231957/2 "2014-09-10T19:49:31Z")
Hello! On Tue, Sep 09, 2014 at 02:25:15PM -0400, gthb wrote: > 2014/09/09 17:41:02 [debug] 91211#0: \*13 http cache key: “” > > To get rid of this gotcha, I suggest either: > > 1. log a warning whenever a location/server/http block has uwsgi\_cache set > but no uwsgi\_cache\_key set. Yes, this is mostly trivial and certainly makes sense. Patch below. # HG changeset patch # User Maxim D. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) # Date 1410371072 -14400 # Wed Sep 10 21:44:32 2014 +0400 # Node ID bc4ee0b7cf2643fdcea310638302b9cadc7ac939 # Parent aaa82dc56c9460db1b4233fc1d4559fdd07ff7ed Added warning about unset cache keys. In fastcgi, scgi and uwsgi modules there are no default cache keys, and using a cache without a cache key set is likely meaningless. diff --git a/src/http/modules/ngx\_http\_fastcgi\_module.c b/src/http/modules/ngx\_http\_fastcgi\_module.c — a/src/http/modules/ngx\_http\_fastcgi\_module.c +++ b/src/http/modules/ngx\_http\_fastcgi\_module.c @@ -2582,6 +2582,11 @@ ngx\_http\_fastcgi\_merge\_loc\_conf(ngx\_conf conf-\>cache\_key = prev-\>cache\_key; } - if (conf-\>upstream.cache && conf-\>cache\_key.value.data == NULL) { - ``` ngx_conf_log_error(NGX_LOG_WARN, cf, 0, ``` - ``` "no \"fastcgi_cache_key\" for ``` "fastcgi\_cache""); - } - ngx\_conf\_merge\_value(conf-\>upstream.cache\_lock, prev-\>upstream.cache\_lock, 0); diff --git a/src/http/modules/ngx\_http\_scgi\_module.c b/src/http/modules/ngx\_http\_scgi\_module.c — a/src/http/modules/ngx\_http\_scgi\_module.c +++ b/src/http/modules/ngx\_http\_scgi\_module.c @@ -1337,6 +1337,11 @@ ngx\_http\_scgi\_merge\_loc\_conf(ngx\_conf\_t conf-\>cache\_key = prev-\>cache\_key; } - if (conf-\>upstream.cache && conf-\>cache\_key.value.data == NULL) { - ``` ngx_conf_log_error(NGX_LOG_WARN, cf, 0, ``` - ``` "no \"scgi_cache_key\" for \"scgi_cache\""); ``` - } - ngx\_conf\_merge\_value(conf-\>upstream.cache\_lock, prev-\>upstream.cache\_lock, 0); diff --git a/src/http/modules/ngx\_http\_uwsgi\_module.c b/src/http/modules/ngx\_http\_uwsgi\_module.c — a/src/http/modules/ngx\_http\_uwsgi\_module.c +++ b/src/http/modules/ngx\_http\_uwsgi\_module.c @@ -1524,6 +1524,11 @@ ngx\_http\_uwsgi\_merge\_loc\_conf(ngx\_conf\_t conf-\>cache\_key = prev-\>cache\_key; } - if (conf-\>upstream.cache && conf-\>cache\_key.value.data == NULL) { - ``` ngx_conf_log_error(NGX_LOG_WARN, cf, 0, ``` - ``` "no \"uwsgi_cache_key\" for ``` "uwsgi\_cache""); - } - ngx\_conf\_merge\_value(conf-\>upstream.cache\_lock, prev-\>upstream.cache\_lock, 0); – Maxim D. > **[nginx](http://nginx.org/)**