Actions after cache miss is detected

[Maxim Dounin]

Hello!

On Fri, Aug 10, 2018 at 09:05:30AM -0700, Roger Fischer wrote:

> Is there a way to perform an action after a cache miss is 
> detected but before the request is forwarded to the upstream 
> server?
> 
> Specifically, on a cache miss I want to:
> Return a response instead of forwarding the request to the 
> upstream server.
> Trigger a handler (module or script) that executes 
> asynchronously to the request.
> 
> The latter I could do by looking at the logs. But I was 
> wondering if there is a more elegant way.

There is no direct way to do this.  There are multiple of ways to 
do this indirectly though, including:

- configure a backend which returns a non-cacheable response and 
  triggers appropriate actions;

- configure a non-responding backend and error_page 502 to return 
  a response and trigger appropriate processing.

Alternatively, in some cases it might be more convenient to use 
proxy_store instead of proxy_cache, and then work with responses 
on the file system - with try_files and so on.

-- 
Maxim Dounin
http://mdounin.ru/