Handler invokation after upstream server being picked

Jan Algermissen jan.algermissen at nordsc.com
Tue Nov 12 14:28:48 UTC 2013


a while ago you replied to my question below. 

Since yesterday I am trying to get hold of the proxy_host variable set by the proxy module but without success, maybe you can help a little with the code.

From the source I understood that the proxy module sets the proxy_host var during NGINX startup. I guess, that happens on a per-location basis, depending on encountering a proxy_pass directive.


I should then be able to access the proxy_host variable during the authentication phase (this is where my module sits).


To get hold of it, I try to find the index of the proxy_host var in my location config merge handler:

    var.data = (unsigned char*)"proxy_host";
    var.len = 10;
    child->proxy_host_var_index = ngx_http_get_variable_index(cf, &var);
    if (child->proxy_host_var_index == NGX_ERROR) {  /* NOT FOUND, TRY TO INHERIT */
        child->proxy_host_var_index = parent->proxy_host_var_index;
        return NGX_CONF_OK;

  /* FOUND - This loca config has its own proxy_pass configuration */

In my handler, I then do this:

   ngx_http_variable_value_t  *value;
    value = ngx_http_get_indexed_variable(r, conf->proxy_host_var_index);
Does that make sense? I does not work for me, unfortunately.

(The log module does see the proxy_host variable and logs the expected value for it.


> Hello!
> On Fri, Oct 25, 2013 at 12:30:34PM +0200, Jan Algermissen wrote:
>> Hi,
>> I am writing a module that needs to add/change the HTTP 
>> Authorization server for an upstream request.
>> Since I am using a signature based authentication scheme where 
>> the signature base string includes the request host and port the 
>> header can only be added *after* the upstream module has 
>> determined which server to send the request to (e.g. after 
>> applying round-robin).
>> Is it possible to hook my module into that 'phase' and if so - 
>> what is the preferred way to do that?
>> I saw that I at least can access the target host and port set by 
>> the proxy module by reading the proxy module variables. However, 
>> that (of course) does only give the server group name to be used 
>> by the upstream module in the next step.
> A request to an upstream is created once, before a particular 
> server is known, and the same request is used for requests to all 
> upstream servers.  That is, what you are trying to do isn't 
> something currently possible.
> -- 
> Maxim Dounin

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