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NgxWSGIModule

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Nginx WSGI module

Updates

This is a copy of the page at http://hg.mperillo.ath.cx/nginx/mod_wsgi/file/tip/README

Always check that page for updated information.

Important Notes

From LoONeYChIKuN: I was able to successfully get this to compile on 0.8.30 and 0.7.64 using this patch.
From JacobSingh: I tested this against 0.6.23 and it didn't compile.
Error was:
rc/ngx_http_wsgi_handler.c: In function 'ngx_http_wsgi_handler':
/root/mod_wsgi-8994b058d2db/src/ngx_http_wsgi_handler.c:74: warning: implicit declaration of function 'ngx_http_discard_body'
make[1] : *** [objs/addon/src/ngx_http_wsgi_handler.o] Error 1
make[1] : Leaving directory /tmp/src-0.6.32-orig
Possible Solution
You should change that line to read ngx_http_discard_request_body(

Introduction

mod_wsgi is an implementation of the Python Web Server Gateway Interface v1.0 for the Nginx web server.

Nginx is a fast asynchronous HTTP server.

The design of this software was in part influenced by the mod_wsgi module for Apache by Graham Dumpleton and obtainable from http://www.modwsgi.org. This software also contains code from the Apache mod_wsgi module and is being used here with the permission of Graham Dumpleton.

Installation

mod_wsgi has been tested with Nginx 0.5.34. Other versions may require patches (see patches/README).

  1. Download the Nginx sources from http://nginx.net/ and unpack it.
  2. Building Nginx
    • change to the directory which contains the Nginx sources
    • run the configuration script making sure to add the path to the mod_wsgi sources using the --add-module option.
    • It is recommended to enable debugging. ::
      • $ ./configure --add-module=/path/to/mod_wsgi/ --with-debug
    • Nginx will use as default prefix path the directory /usr/local/nginx.
    • Now you can build and install the software:
      • $ make
      • $ make install (make sure to be root when calling make install)

mod_wsgi tested with Nginx 0.8.31 and python-2.6.2

  1. Download the Nginx sources from http://nginx.net/ and unpack it.
  2. Building instructions same as above.

Special Cases

OSX

If the config script tells you something like this:
:: checking for wsgi ... not found
:: ./configure: error: the WSGI addon requires Python library.
diff -r a338320b9197 config
--- a/config    Sun Jan 06 15:15:25 2008 +0100
+++ b/config    Tue Jan 08 10:49:11 2008 -0600
@@ -18,7 +18,7 @@ ngx_feature_run=no
ngx_feature_run=no
ngx_feature_incs="#include <Python.h>"
ngx_feature_path=${PYTHON_PATH}
-ngx_feature_libs="-L ${PYTHON_LIBDIR} ${PYTHON_LDFLAGS} -lpython${PYTHON_VERSION}"
+ngx_feature_libs="-L${PYTHON_LIBDIR} ${PYTHON_LDFLAGS} -lpython"
ngx_feature_test="Py_Initialize()"
. auto/feature
Removing the version number from the lib directive got it to configure on OS X 10.4.

Examples

In the mod_wsgi distribution, there are some examples in the examples directory.

Design goals of mod_wsgi

  1. make everything as simple as possible, but not simpler.
  2. Nginx is not Apache, it is not designed to support generic embedded modules.
  3. If a module blocks, the entire application will blocks.
  4. This is somewhat mitigated by the fact that Nginx uses an arbitrary number of worker process.
  5. Unlike Apache, the number of worker processes in nginx is fixed.

So why implement a wsgi module for nginx?

  1. The reason is: because writing a module for an existing web server is easier that write a web server from scratch.
  2. Nginx is a very efficient web server and its code and memory usage is very compact.
  3. Mod_wsgi can be used for a fast deployment with *batteries included*, as a replacement for the Python standard HTTP server.
  4. mod_wsgi can also be used for a robust deployment with mod_proxy, as a replacement for a Python FastCGI implementation like flup
  5. In a shared hosting this is valuable, since mod_wsgi usually requires less resources than a pure Python server.

Future

Since Nginx is a *pure* asynchronous server, without threads support, it is important to implement WSGI extensions for asynchronous programming

Directives

.. main configuration commands

wsgi_python_optimize ++++++++++++++++++++

Syntax: wsgi_python_optimize *n*
Default: wsgi_python_optimize 0
Context: http, server, location
Description:
Directive sets the optimization level of the Python compiler.
This is equivalent to the -O option of the Python Interpreter.

wsgi_python_executable ++++++++++++++++++++++

Syntax: wsgi_python_executable *path*
Default:
Context: http, server, location
Description:
Directive sets the path to the python interpreter executable.
This value is used to find the Python run-time libraries relative
to the interpreter executable.

wsgi_python_home ++++++++++++++++

Syntax: wsgi_python_home *path*
Default:
Context: http, server, location
Description:
XXX

wsgi_enable_subinterpreters +++++++++++++++++++++++++++

Syntax: wsgi_enable_subinterpreters *on | off*
Default: wsgi_enable_subinterpreters off
Context: http, server, location
Description:
Directive enables the use of sub interpreters.
When enabled, each WSGI application will be executed in a separate
sub interpreter, unless wsgi_use_main_interpreter_ directive is
used.
    • NOTE**: some applications may have problems when executed inside
a subinterpreter.

.. location configuration commands

wsgi_pass_authorization +++++++++++++++++++++++

Syntax: wsgi_pass_authorization *on | off*
Default: wsgi_pass_authorization off
Context: http, server, location
Description:
By default, as suggested by the CGI spec, mod_wsgi does not pass
the Authorization header to the WSGI application.
Enable this directive if the WSGI application handles HTTP
authentication.

wsgi_allow_ranges +++++++++++++++++

Syntax: wsgi_allow_ranges *on | off*
Default: wsgi_allow_ranges off
Context: http, server, location
Description:
Directive enables integrated support to partial HTTP requests,
using the nginx range filter module.
    • NOTE**: in the current version nginx supports ranges for single
buffer responses only.

wsgi_script_reloading +++++++++++++++++++++

Syntax: wsgi_script_reloading *on | off*
Default: wsgi_script_reloading off
Context: http, server, location
Description:
If enabled, mod_wsgi will check, at every request, if the WSGI
script has been modified.
If the script has been modified, it will reload the application
using the reload mechanism specified in the
wsgi_reload_mechanism directive.

wsgi_reload_mechanism +++++++++++++++++++++

Syntax: wsgi_reload_mechanism *module | process*
Default: wsgi_script_reloading module
Context: http, server, location
Description:
This directive specifies how to reload a WSGI application whose
file has been modified.
When module mechanism is in use, mod_wsgi will remove the script
module from the system modules dictionary and will reload it.
When process mechanism is in use, mod_wsgi will raise a QUIT
signal.
This signal will request Nginx to do a graceful shutdown of the
process (see the Nginx documentation for detailed info).
The current request is served using the *old* WSGI application, but
mod_wsgi will add a Refresh: 0 header, so that clients that
recognize this header can execute a new request to obtain the
updated resource.
    • NOTE**:
it is possible to reload a WSGI application by sending a
HUP signal to the master process.
See http://wiki.codemongers.com/NginxCommandLine for more info.
    • WARNING**: if the master process is not active, the Nginx process
will be terminated.

wsgi_optimize_send_headers ++++++++++++++++++++++++++

Syntax: wsgi_optimize_send_headers *on | off*
Default: wsgi_optimize_send_headers off
Context: http, server, location
Description:
Directive enables to optimize away content generation, when HTTP
request does not requires a response body (as an example for HEAD
request, or for a GET request when the client has a fresh cache of
the resource entity).
For an effective use of this optimization, the WSGI application
must return a generator and yield an empty string after having
called start_response.
    • NOTE**: WSGI spec explicitly requires that the headers must be
sent when the first not empty string is yielded.

wsgi_output_buffering +++++++++++++++++++++

Syntax: wsgi_output_buffering *on | off*
Default: wsgi_output_buffering off
Context: http, server, location
Description:
When output buffering is enabled, Nginx can buffer the data yielded
by the WSGI application iterable.
This increments the performance, especially if the application yield
small strings.
Note however that the WSGI spec recommend that the buffering should
be done by the application and not by the gateway.
    • BUG**: there seems to be problems when this directive is enabled.

wsgi_write_buffering +++++++++++++++++++++

Syntax: wsgi_write_buffering *on | off*
Default: wsgi_write_buffering off
Context: http, server, location
Description:
This directive activates buffering of the write callable.
If buffering is activated, then mod_wsgi will store all the data
written by the WSGI application in a buffer, assigned by directive
wsgi_write_buffer_size.
The headers will be sent only when the WSGI application returns.
If the data can not all be placed in memory, then parts of it will
be written to disk.
If buffering is switched off, then the data is *synchronously*
transferred to client immediately.
    • NOTE**: WSGI explicitly requires that the WSGI gateway **must**
not buffer the data.
    • NOTE**: sending data synchronously can have a severe impact on
nginx performances.

wsgi_write_buffer_size ++++++++++++++++++++++

Syntax: wsgi_write_buffer_size *buffer_size*
Default: wsgi_write_buffer_size 4k/8k
Context: http, server, location
Description:
This directive controls the size of the buffer to use.
By default, the size of the buffer is equal to the size of
page. Depending on platform this is either 4K or 8K.

wsgi_temp_path ++++++++++++++

Syntax: wsgi_temp_path *dir-path [ level1 [ level2 [ level3 ] *
Default: $NGX_PREFIX/wsgi_temp controlled by NGX_HTTP_WSGI_TEMP_PATH in configure script
Context: http, server, location
Description:
This directive works like client_body_temp_path to specify a
location to buffer large data generated by the write callable, if
wsgi_write_buffering is enabled.

wsgi_var ++++++++

Syntax: wsgi_var *variable value*
Default:
Context: http, server, location
Description:
Directive assigns the variable, which will be added to the
environment dictionary passed to the WSGI application.
It is possible to use strings, nginx variables and their
combination as values. Directives not set are inherited from the
outer level.
    • NOTE**:
variables defined using this directive are added to the
environment dictionary after HTTP headers, so user can override
these values.
It can be useful, as an example, to override HTTP_COOKIE with: ::
wsgi_var HTTP_COOKIE $http_cookie;
since the $http_cookie variable combines multiple Cookie headers.

wsgi_use_main_interpreter +++++++++++++++++++++++++

Syntax: wsgi_use_main_interpreter *on | off*
Default: wsgi_use_main_interpreter off
Context: http, server, location
Description:
Directive enables the execution of the WSGI application using the
main Python interpreter.
This directive is only used when wsgi_enable_subinterpreters_
directive is enabled.

wsgi_middleware +++++++++++++++

Syntax: wsgi_middleware *module_name [callable_name] *
Default: wsgi_pass module_name "middleware"
Context: http, server, location
Description:
Directive push the specified middleware in the middleware stack.

wsgi_pass +++++++++

Syntax: wsgi_pass *module_path [callable_name] *
Default: wsgi_pass module_path "application"
Context: location, if in location, limit_except
Description:
Directive assigns the module path and the callable name of the WSGI
application to execute.