location.capture and proxy_pass

tzury · 2012-05-22T18:01:02+00:00

2012/5/22 wei deng <dengwei28@gmail.com> > > 最近一直在学习nginx 在网上看&#x8fc...

location.capture and proxy_pass

tzury

Hi,

In a setup of nginx as reversed proxy, I am using the location.capture to fetch data from back-end server and analyze it before submitting it to the client.

My questions are:

1. Looking at back-end server's logs shows that capture and proxy_pass both executed meaning each request to nginx causes two requests to the back-end server.

2. I wish location.capture to take exclusive control over what will be sent back to client, how can I do so using ngx.print?

agentzh

On Tue, May 22, 2012 at 6:00 PM, Tzury Bar Yochay <tz...@reblaze.com> wrote:
>
> In  a setup of nginx as reversed proxy, I am using the location.capture to
> fetch data from back-end server and analyze it before submitting it to the
> client.
> My questions are:
>
> 1. Looking at back-end server's logs shows that capture and proxy_pass
> both executed meaning each request to nginx causes two requests to the
> back-end server.

This should not happen. If it's indeed the case, then there must be a
bug somewhere. Can you prepare a minimized example that can help
reproducing this issue on *my* side?

> 2. I wish location.capture to take exclusive control over what will be
> sent back to client, how can I do so using ngx.print?
>

It should.

Regards,
-agentzh

tzury

This should not happen. If it's indeed the case, then there must be a
bug somewhere. Can you prepare a minimized example that can help
reproducing this issue on *my* side?

Below are the two files involved, the lua and the conf.

The log I am looking at is the apache's back-end which provide 2 lines per request.

-----8<-----8<-----8<----- my_proxy.lua -----8<-----8<-----8<-----

local ngx = require "ngx"

-- do nothing at the moment

local res = ngx.location.capture(ngx.var.request_uri)

-----8<-----8<-----8<----- nginx.conf -----8<-----8<-----8<-----

http {
default_type application/octet-stream;

upstream local_apache {
server localhost:8080;
}

sendfile on;
keepalive_timeout 65;

gzip on;

lua_regex_cache_max_entries 51200;

server {

listen 8880;
server_name localhost;
access_log /var/log/http.access.log ;
error_log /var/log/http.error.log ;

lua_need_request_body on;
access_by_lua_file /tmp/my_proxy.lua;

location / {
proxy_pass http://local_apache;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
more_clear_headers 'server*';
more_clear_headers 'Server*';
}

}

}

> 2. I wish location.capture to take exclusive control over what will be
> sent back to client, how can I do so using ngx.print?
>

It should.

How's that should be done?

agentzh

On Tue, May 22, 2012 at 6:17 PM, Tzury Bar Yochay <tz...@reblaze.com> wrote:
> Below are the two files involved, the lua and the conf.
> The log I am looking at is the apache's back-end  which provide 2 lines per
> request.
>
> -----8<-----8<-----8<-----  my_proxy.lua -----8<-----8<-----8<-----
>
> local ngx           = require "ngx"
>
> -- do nothing at the moment
> local res = ngx.location.capture(ngx.var.request_uri)
>
>
>
> -----8<-----8<-----8<-----  nginx.conf -----8<-----8<-----8<-----
>
[...]
>
>         lua_need_request_body on;
>         access_by_lua_file /tmp/my_proxy.lua;
>

Okay...you're using access_by_lua here. I thought you were using content_by_lua.

The nginx processes requests in phases, and common phases run in the order like:

     rewrite phase => access phase => content phase

Your access_by_lua runs in the access phase while proxy_pass runs in
the content phase. So your Lua code runs first, and then nginx
continues to run proxy_pass after that.

To short-circuit the processing flow, i.e., to finish the whole
request processing cycle in your Lua code running at the access phase,
you need to use ngx.exit(200) (or something like that) at the end of
your access_by_lua's Lua script, see

    http://wiki.nginx.org/HttpLuaModule#ngx.exit

You can learn more about the nginx request processing phases by
reading the English transcript of my Nginx serial tutorials here:

    http://agentzh.org/misc/nginx/agentzh-nginx-tutorials-enuk.html

Regards,
-agentzh

tzury

To short-circuit the processing flow, i.e., to finish the whole
request processing cycle in your Lua code running at the access phase,
you need to use ngx.exit(200) (or something like that) at the end of
your access_by_lua's Lua script, see

thanks for clarification.

so assume I want to handle the request (from client side) at access phase,

and response (from back-end server) at content phase, is it possible?

(this approach make sense to me as I do not wish to replace the entire proxy capability with

the lua function)

how hooking code should look like?

agentzh

On Tue, May 22, 2012 at 6:57 PM, Tzury Bar Yochay <tz...@reblaze.com> wrote:
>> To short-circuit the processing flow, i.e., to finish the whole
>> request processing cycle in your Lua code running at the access phase,
>> you need to use ngx.exit(200) (or something like that) at the end of
>> your access_by_lua's Lua script, see
>
>
> thanks for clarification.
>
> so assume I want to handle the request (from client side) at access phase,
> and response (from back-end server) at content phase, is it possible?
>

If subrequests are involved here, then each (sub)request has its own
processing phases.

For example, if your main request (to /main) issues a subrequest (to
/sub) at access phase by calling ngx.location.capture(), then the
running phases looks like:

    /main        /sub
    access
                    rewrite
                    access
                    content
    access
    content

That is, the access phase of /main will stay until the /sub completes
all of its own phases.

> (this approach make sense to me as  I do not wish to replace the entire
> proxy capability with
> the lua function)
>

In your case, I think you should use content_by_lua instead of access_by_lua.

Regards,
-agentzh