Nginx, echo module & lua

Server NGINX
1

Hi all,

I’m trying to use both echo module & lua, but I’m having some issues:

  1. I reach quickly “subrequests cycle”. Looking @ the code, subrequests
    is unsigned:8,
    but I would need thousands of subrequests sometimes. putting
    subrequests to unsigned just
    results to crashes.

  2. when in config: set_by_lua_file $varname luafile.lua , and
    luafile.lua references to ngx.ctx,
    I get the following error:
    (lua-error)…no request ctx found
    according to the doc, ngx.ctx is available in set_lua*, but does not
    work. Would anybody suggest
    me a workaround ?

I’m using luajit, openresty last version.

Thanks a lot in advance,
Pierre

2

Hello!

On Wed, May 2, 2012 at 4:11 PM, Pierre [email protected] wrote:

I’m trying to use both echo module & lua, but I’m having some issues:

  1. I reach quickly “subrequests cycle”. Looking @ the code, subrequests is
    unsigned:8,
    but I would need thousands of subrequests sometimes. putting subrequests to
    unsigned just
    results to crashes.

There’s no way to support thousands of subrequests in a single main
request without patching the nginx core.

But you’re encouraged to try out ngx_lua’s cosocket API to avoid
subrequests altogether. And the cosocket stuff does not have such
limitations.

There’s already several Lua drivers based on that, including
memcached, redis, mysql, http, and mongodb. For instance, the
lua-resty-redis library:

  1. when in config: set_by_lua_file $varname luafile.lua , and luafile.lua
    references to ngx.ctx,
    I get the following error:
    (lua-error)…no request ctx found
    according to the doc, ngx.ctx is available in set_lua*, but does not work.
    Would anybody suggest
    me a workaround ?

This is indeed a bug. Thanks for reporting this!

I’ve just committed a patch for it:

Could you try out the git master HEAD on your side?

Thanks!
-agentzh

3

On 02/mai - 19:46, agentzh wrote:

There’s no way to support thousands of subrequests in a single main
request without patching the nginx core.
ok

But you’re encouraged to try out ngx_lua’s cosocket API to avoid
subrequests altogether. And the cosocket stuff does not have such
limitations.
hmm, any more documentation about that ?
More about: how to implement it in my lua scripts ?

is that it ? :

local tcp = ngx.socket.tcp

function new(self)
return setmetatable({ sock = tcp() }, mt)
end

?

There’s already several Lua drivers based on that, including
memcached, redis, mysql, http, and mongodb. For instance, the
lua-resty-redis library:
mongodb: you mean mongofs or mongodb ?

This is indeed a bug. Thanks for reporting this!

I’ve just committed a patch for it:

bugfix: ngx.ctx was not accessible at all in set_by_lua*. thanks Pierre. · openresty/lua-nginx-module@bee1cab · GitHub
woh, thx !

Could you try out the git master HEAD on your side?
I will

4

On Wed, May 2, 2012 at 9:39 PM, Pierre [email protected] wrote:

But you’re encouraged to try out ngx_lua’s cosocket API to avoid
subrequests altogether. And the cosocket stuff does not have such
limitations.
hmm, any more documentation about that ?

See the official documentation for ngx_lua cosocket:

http://wiki.nginx.org/HttpLuaModule#ngx.socket.tcp

More about: how to implement it in my lua scripts ?

is that it ? :

local tcp = ngx.socket.tcp

function new(self)
return setmetatable({ sock = tcp() }, mt)
end
?

See the lua-resty-redis, lua-resty-memcached, and lua-resty-mysql
libraries as examples:

https://github.com/agentzh/lua-resty-redis
https://github.com/agentzh/lua-resty-memcached
https://github.com/agentzh/lua-resty-mysql

bigplum has been working on lua-resty-mongol:

https://github.com/bigplum/lua-resty-mongol

I’m not sure about its state, but you can read the document or contact
the author directly.

Best regards,
-agentzh

5

A little thread hijacking. Are there plans to provide an HTTP response
parser? I suppose that for performance reasons that would have to
be in C along the lines of the Redis parser.

That’s what’s missing, IMHO, in order to completely replace
luasocket.

Great work as usual.

–appa

6

Investigating a bit more, here is the conclusion:

location = /store {
internal;
#test 1
#echo_subrequest_async PUT /trucalacon -q ‘filename=$arg_filename’
-b $echo_request_body;
#test 2
#content_by_lua ’

local filename = ngx.req.get_uri_args()[“md5”]

local res = ngx.location.capture(“/trucalacon”,

{ args = {filename = filename } ,

ctx = ngx.ctx })

#';
}
location = /trucalacon {
proxy_set_header X-Real-IP $remote_addr;
proxy_pass http://otherserver;
}

using echo_subrequest_async, I directly reach :
2012/05/03 12:08:25 [error] 13204#0: *1 subrequests cycle while
processing “/trucalacon”,

using echo_subrequest, I get the same behaviour as ngx.location.capture

using content_by_lua + location.capture, everything is smooth.

/store is called by another lua script, which does
location.capture.multi(‘/store’), 20 by 20

Last interrogation:
What is the best way to discard body (I mean free the memory by body
passed to subrequests ) ?

7

On 02/mai - 19:46, agentzh wrote:

lua-resty-redis library:

GitHub - openresty/lua-resty-redis: Lua redis client driver for the ngx_lua based on the cosocket API

how can I combine cosocket & foreign upstream ?
also, I didn’t find any example involving cosocket between locations, or
maybe
I’m getting it wrong.

I’ve just committed a patch for it:

bugfix: ngx.ctx was not accessible at all in set_by_lua*. thanks Pierre. · openresty/lua-nginx-module@bee1cab · GitHub

works like a charm, thanks !

8

On Thu, May 3, 2012 at 3:53 PM, Antonio P.P. Almeida [email protected]
wrote:

A little thread hijacking. Are there plans to provide an HTTP response
parser? I suppose that for performance reasons that would have to
be in C along the lines of the Redis parser.

GitHub - openresty/lua-redis-parser: Lua module for parsing raw redis responses

That’s what’s missing, IMHO, in order to completely replace
luasocket.

Liseen Wan has been working on the lua-resty-http library:

https://github.com/liseen/lua-resty-http

We’ll extend that to support more and more HTTP features in the near
future.

But I think it will remain pure Lua because introducing C may not
really help here given the performance of LuaJIT 2.0 (and it has
already been proven in lua-resty-mysql where rewriting the MySQL
packet parser in C actually slowed things down because going across
language boundary is more expensive).

But anyway we can provide pure C API for ngx_lua cosocket, just like
ngx_http_upstream, so a pure C implementation for those lua-resty-*
library will have a chance to achieve better performance than the pure
Lua implementations, but I’m not 100% sure :wink:

Regards,
-agentzh

9

On Thu, May 3, 2012 at 7:34 AM, Pierre [email protected] wrote:

The cosocket API is used to talk to remote servers in TCP or unix
domain sockets directly. It does not support the subrequest model at
all so it is not used for reusing existing upstream modules.

The “cosocket” term is short for “coroutine-based socket”, it is a
parallel implementation as ngx_http_usptream, see the following graph:

http://agentzh.org/misc/slides/libdrizzle-lua-nginx/#57

I’ve just committed a patch for it:

bugfix: ngx.ctx was not accessible at all in set_by_lua*. thanks Pierre. · openresty/lua-nginx-module@bee1cab · GitHub

works like a charm, thanks !

Sorry, my previous patch introduced a bad memory leak and I’ve just
committed the following patch to fix this:

https://github.com/chaoslawful/lua-nginx-module/commit/8d2878

Best regards,
-agentzh

10

On 03/mai - 21:03, agentzh wrote:

On Thu, May 3, 2012 at 6:43 PM, Pierre [email protected] wrote:

using echo_subrequest_async, I directly reach :
2012/05/03 12:08:25 [error] 13204#0: *1 subrequests cycle while processing
“/trucalacon”,

Which version of nginx are you using?
tested on openresty 10.0.10 abd 1.0.11
the lifetime of the main request.
ok, thx

It’s worth mentioning that the ngx_lua cosocket API does not suffer
from this issue because Lua GC handles the resource lifetime there.
:slight_smile:

11

On Thu, May 3, 2012 at 6:43 PM, Pierre [email protected] wrote:

using echo_subrequest_async, I directly reach :
2012/05/03 12:08:25 [error] 13204#0: *1 subrequests cycle while processing
“/trucalacon”,

Which version of nginx are you using?

Last interrogation:
What is the best way to discard body (I mean free the memory by body passed to
subrequests ) ?

There’s no way to release all the memory of a subrequest instantly
because nginx subrequests share the same memory pool as their parent
request. So for long-running requests that issue a lot of serial
subrequests, there will be a good chance of temporary memory leaks in
the lifetime of the main request.

It’s worth mentioning that the ngx_lua cosocket API does not suffer
from this issue because Lua GC handles the resource lifetime there.

Best regards,
-agentzh