# Setting cache parameters via if directives

**URL:** <https://www.ruby-forum.com/t/setting-cache-parameters-via-if-directives/202397>\
**Category:** NGINX\
**Created:** [January 28, 2011, 6:09am UTC](https://www.ruby-forum.com/t/setting-cache-parameters-via-if-directives/202397 "2011-01-28T06:09:44Z")\
**Posts on this page:** 8\
**Page:** 1

<div class="post-metadata">

**Author:** ![luislavena](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/0ea827/32.png) [@luislavena](https://www.ruby-forum.com/u/luislavena)\
**Post date:** [January 28, 2011, 6:09am UTC](https://www.ruby-forum.com/t/setting-cache-parameters-via-if-directives/202397/1 "2011-01-28T06:09:44Z")

</div>

Hello,

We have a particular application (gitweb) that performs a particular,  
extraordinarily slow function when the home page is loaded. As the  
number of repositories has increased, this has grown to take several  
_minutes_ per page view (yes, ugh).

To combat this, we tried setting up cache so that this only occurs once  
an hour, but it’s still causing too much of a problem…both because it  
doesn’t always last an hour (sometimes we see the delay happen again  
sooner) and because when it does expire, it simply takes too long (and  
if multiple clients connect at that same time making that request, it  
gets even worse).

As a result, what I’d like to do is to have the cache expire after an  
hour, but once every twenty or thirty minutes manually refresh the  
cache. That way clients can use the existing cache while the new page is  
being rebuilt, which will then save the new values into the cache and  
reset the timer.

So my thought was that I could do something like the code below, but it  
doesn’t work since I can’t put the directives I want into the if block,  
and the proxy\_pass in the if block (if I remove the cache values) honors  
the cache values in the outside location block anyways:

```
location = / {
    if ($remote_addr = "1.2.3.4") {
        proxy_pass http://127.0.0.1:80;
        proxy_cache gitweb;
        proxy_cache_valid 200 20m;
        proxy_read_timeout 300;
        proxy_send_timeout 300;
    }
    proxy_pass http://127.0.0.1:80;
    proxy_cache gitweb;
    proxy_cache_valid 200 60m;
    proxy_cache_use_stale off;
    proxy_read_timeout 60;
    proxy_send_timeout 60;
}

```

Any help much appreciated.

Thanks,  
Jeff

---

<div class="post-metadata">

**Author:** ![sithadmin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/858c86/32.png) [@sithadmin](https://www.ruby-forum.com/u/sithadmin)\
**Post date:** [January 28, 2011, 4:57pm UTC](https://www.ruby-forum.com/t/setting-cache-parameters-via-if-directives/202397/2 "2011-01-28T16:57:25Z")

</div>

On Thu, Jan 27, 2011 at 11:08 PM, Jeff M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> ```
> proxy_cache_valid 200 60m;
> proxy_cache_use_stale off;
> proxy_read_timeout 60;
> proxy_send_timeout 60;
> 
> ```
> 
> }
> 
> Any help much appreciated.

I do something similar using the conditinal setting of variables  
inside the if block to set Cache-Control values, perhaps you can use a  
similar method to set the values of proxy\_cache\_valid. Since setting  
variables is one of the few “safe” things to do inside an if block,  
and most directives can take variables as agurments, it is generally  
useful.

location / {  
set $mycc = “private, max-age=0”;

if ($foo = “bar”) {  
set $mycc = “public, max-age=3600”  
}

proxy\_pass [http://backend](http://backend);  
add\_header Cache-Control $mycc;  
}

–  
RPM

---

<div class="post-metadata">

**Author:** ![sithadmin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/858c86/32.png) [@sithadmin](https://www.ruby-forum.com/u/sithadmin)\
**Post date:** [January 29, 2011, 5:07pm UTC](https://www.ruby-forum.com/t/setting-cache-parameters-via-if-directives/202397/3 "2011-01-29T17:07:29Z")

</div>

On 01/29/2011 03:19 AM, Jeff M. wrote:

> > if ($foo = “bar”) {  
> > set $mycc = “public, max-age=3600”  
> > }
> > 
> > proxy\_pass [http://backend](http://backend);  
> > add\_header Cache-Control $mycc;  
> > }
> 
> Great idea, thank you.

Unfortunately, this doesn’t work:

```
    set $cachevalidval "60m";
    if ($remote_addr = "1.2.3.4") {
        set $cachevalidval "1m";
    }
    proxy_pass http://127.0.0.1:80;
    proxy_cache gitweb;
    proxy_cache_valid any $cachevalidval;

```

I get complaints that $cachevalidval is an invalid time value. I’ve  
tried doing things like having $cachevalidval only have a number and  
then using "$cachevalidval"m but nothing works so far…

Thanks,  
Jeff

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<div class="post-metadata">

**Author:** ![sithadmin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/858c86/32.png) [@sithadmin](https://www.ruby-forum.com/u/sithadmin)\
**Post date:** [January 29, 2011, 9:21am UTC](https://www.ruby-forum.com/t/setting-cache-parameters-via-if-directives/202397/4 "2011-01-29T09:21:13Z")

</div>

On 01/28/2011 10:55 AM, Ryan M. wrote:

> if ($foo = “bar”) {  
> set $mycc = “public, max-age=3600”  
> }
> 
> proxy\_pass [http://backend](http://backend);  
> add\_header Cache-Control $mycc;  
> }

Great idea, thank you.

–Jeff

---

<div class="post-metadata">

**Author:** ![sithadmin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/858c86/32.png) [@sithadmin](https://www.ruby-forum.com/u/sithadmin)\
**Post date:** [January 30, 2011, 12:59am UTC](https://www.ruby-forum.com/t/setting-cache-parameters-via-if-directives/202397/5 "2011-01-30T00:59:16Z")

</div>

Hello Jeff…

On Fri, Jan 28, 2011 at 3:08 AM, Jeff M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> sooner) and because when it does expire, it simply takes too long (and  
> if multiple clients connect at that same time making that request, it  
> gets even worse).

I think you look the wrong way at the problem you have. You should fix  
these  
issues you mention which are NOT the expected behavior before trying to  
fix  
your situation with your proposed patch of allowing a different time to  
a  
special IP and leave a bot requesting the page.

First problem: early renewal of page.

This is not a mistery why it happens: Either your server it’s returning  
a  
header that tells nginx to refresh the cache, or you have a problem  
inside  
your configuration. If you tell nginx to update each 60 min, it will  
always  
respect that except backend server tells nginx to refresh the cache.

Second problem: multiple clientes renewing cache.

This can easily be fixed by using proxy\_cache\_stale, you can set it up  
to  
return users the last cached page while the backend ends updating the  
first  
request that expired. This means that after a requests pass to the  
backend,  
while that request does not complete, nginx will return the last cached  
(which already expired) version to any new request for that page.

If you fix those both problems then I think you won’t need all that  
workaround you want to do.

I’m not nginx guru and maybe it’s me looking the wrong way at your  
problem  
but in case it help this is how I dealt before with the same problem you  
described.

Good Luck!

Guzmn B.

---

<div class="post-metadata">

**Author:** ![sithadmin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/858c86/32.png) [@sithadmin](https://www.ruby-forum.com/u/sithadmin)\
**Post date:** [February 1, 2011, 9:48am UTC](https://www.ruby-forum.com/t/setting-cache-parameters-via-if-directives/202397/6 "2011-02-01T09:48:41Z")

</div>

On Fri, Jan 28, 2011 at 11:55 PM, Ryan M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> if ($foo = “bar”) {  
> set $mycc = “public, max-age=3600”  
> }
> 
> proxy\_pass [http://backend](http://backend);  
> add\_header Cache-Control $mycc;  
> }

I’m amazed to see the config above works for you. I’m not sure if  
you’re using some ancient versions of nginx that I know very little  
about (like 0.6.x or 0.5.x or even earlier).

Consider the following config snippet:

```
location /test {
    set $a 3;
    if ($a = 3) {
        set $a 4;
    }
    echo $a;
}

```

GET /test will give you nothing for nginx 0.7.21 ~ 0.9.4. Don’t tell  
me that the ngx\_echo module’s echo directive is buggy because it’s too  
dead simple to get wrong.

Basically for “modern” versions of nginx, the location “if” block  
creates an anonymous nested location and will trap the execution flow,  
that is, once you get in, you’ll never go out of it to reach the  
content phase. And that’s one of the reasons why people call nginx’s  
“if” an evil monster 😉

Cheers,  
-agentzh

---

<div class="post-metadata">

**Author:** ![sithadmin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/858c86/32.png) [@sithadmin](https://www.ruby-forum.com/u/sithadmin)\
**Post date:** [February 1, 2011, 9:55am UTC](https://www.ruby-forum.com/t/setting-cache-parameters-via-if-directives/202397/7 "2011-02-01T09:55:00Z")

</div>

On Tue, Feb 1, 2011 at 4:47 PM, agentzh [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> GET /test will give you nothing for nginx 0.7.21 ~ 0.9.4.  
> Forgot to mention that we’ve been in favor of ngx\_lua’s set\_by\_lua and  
> rewrite\_by\_lua directives to do something like this:

```
location /test {
    set $a 3;
    set_by_lua $a '
        if ngx.var.a == "3" then
            return 4
        end
    ';
    echo $a;
}

```

and GET /test will give you the expected answer, “4” and the  
performance remains outstanding especially when you’ve enabled LuaJIT  
2.0 😉

Cheers,  
-agentzh

---

<div class="post-metadata">

**Author:** ![sithadmin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/858c86/32.png) [@sithadmin](https://www.ruby-forum.com/u/sithadmin)\
**Post date:** [February 1, 2011, 4:47pm UTC](https://www.ruby-forum.com/t/setting-cache-parameters-via-if-directives/202397/8 "2011-02-01T16:47:40Z")

</div>

On Tue, Feb 1, 2011 at 2:47 AM, agentzh [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> > 
> 
> you’re using some ancient versions of nginx that I know very little  
> }

It does in fact work in production on nginx 0.7.6x. Below is my actual  
configuration (trimmed to the essentials and with a few substitutions  
of actual URIs).

location /MyApp {  
proxy\_pass [http://backendTomcat](http://backendTomcat);  
proxy\_set\_header Host $host;  
proxy\_read\_timeout 900;  
proxy\_next\_upstream error timeout;  
proxy\_redirect [http://example.com/](http://example.com/) $scheme://example.com/;

#hide caching related headers from backend  
#the backend is dumb about this but we can’t change it  
proxy\_hide\_header Pragma;  
proxy\_hide\_header Cache-Control;  
proxy\_hide\_header Expires;

#these variables are the new values for caching headers

set $mycc “private,max-age=0”;  
set $myexp “Fri, 01 Jan 1990 00:34:56 GMT”;

#create a variable that includes both scheme and URI so we  
#can redirect in and out of SSL if needed  
set $schemeuri $scheme$uri;

#add exception for dynamic CSS stylesheet, make it cache for 1 hour  
if ($request\_uri ~\* uiframework.Theme) {  
set $mycc “private,max-age=3600”;  
set $myexp “”;  
}  
if ($schemeuri = “http/MyApp/changePassword”) {  
rewrite ^(.\*)$ https://$host$1 redirect;  
}

#add our new headers  
add\_header “Cache-Control” $mycc;  
add\_header “Expires” $myexp;  
}

–  
RPM