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HttpMemcModule

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[edit] Name

memc-nginx-module - An extended version of the standard memcached module that supports set, add, delete, and many more memcached commands.

This module is not distributed with the Nginx source. See the installation instructions.

[edit] Version

This document describes memc-nginx-module v0.13rc2 released on 24 November 2011.

[edit] Synopsis 

    # GET /foo?key=dog
    #
    # POST /foo?key=cat
    # Cat's value...
    #
    # PUT /foo?key=bird
    # Bird's value...
    #
    # DELETE /foo?key=Tiger
    location /foo {
        set $memc_key $arg_key;
 
        # $memc_cmd defaults to get for GET,
        #   add for POST, set for PUT, and
        #   delete for the DELETE request method.
 
        memc_pass 127.0.0.1:11211;
    }
    # GET /bar?cmd=get&key=cat
    #
    # POST /bar?cmd=set&key=dog
    # My value for the "dog" key...
    #
    # DELETE /bar?cmd=delete&key=dog
    # GET /bar?cmd=delete&key=dog
    location /bar {
        set $memc_cmd $arg_cmd;
        set $memc_key $arg_key;
        set $memc_flags $arg_flags; # defaults to 0
        set $memc_exptime $arg_exptime; # defaults to 0
 
        memc_pass 127.0.0.1:11211;
    }
    # GET /bar?cmd=get&key=cat
    # GET /bar?cmd=set&key=dog&val=animal&flags=1234&exptime=2
    # GET /bar?cmd=delete&key=dog
    # GET /bar?cmd=flush_all
    location /bar {
        set $memc_cmd $arg_cmd;
        set $memc_key $arg_key;
        set $memc_value $arg_val;
        set $memc_flags $arg_flags; # defaults to 0
        set $memc_exptime $arg_exptime; # defaults to 0
 
        memc_cmds_allowed get set add delete flush_all;
 
        memc_pass 127.0.0.1:11211;
    }
  http {
    ...
    upstream backend {
       server 127.0.0.1:11984;
       server 127.0.0.1:11985;
    }
    server {
        location /stats {
            set $memc_cmd stats;
            memc_pass backend;
        }
        ...
    }
  }
  ...
    # read the memcached flags into the Last-Modified header
    # to respond 304 to conditional GET
    location /memc {
        set $memc_key $arg_key;
 
        memc_pass 127.0.0.1:11984;
 
        memc_flags_to_last_modified on;
    }
    location /memc {
        set $memc_key foo;
        set $memc_cmd get;
 
        # access the unix domain socket listend by memcached
        memc_pass unix:/tmp/memcached.sock;
    }

[edit] Description

This module extends the standard memcached module to support almost the whole memcached ascii protocol.

It allows you to define a custom REST interface to your memcached servers or access memcached in a very efficient way from within the nginx server by means of subrequests or independent fake requests.

This module is not supposed to be merged into the Nginx core because I've used Ragel to generate the memcached response parsers (in C) for joy :)

If you are going to use this module to cache location responses out of the box, try HttpSRCacheModule with this module to achieve that.

[edit] Keep-alive connections to memcached servers

You need HttpUpstreamKeepaliveModule together with this module for keep-alive TCP connections to your backend memcached servers.

Here's a sample configuration: 

  http {
    upstream backend {
      server 127.0.0.1:11211;
 
      # a pool with at most 1024 connections
      # and do not distinguish the servers:
      keepalive 1024;
    }
 
    server {
        ...
        location /memc {
            set $memc_cmd get;
            set $memc_key $arg_key;
            memc_pass backend;
        }
    }
  }

[edit] How it works

It implements the memcached TCP protocol all by itself, based upon the upstream mechansim. Everything involving I/O is non-blocking.

The module itself does not keep TCP connections to the upstream memcached servers across requests, just like other upstream modules. For a working solution, see section Keep-alive connections to memcached servers.

[edit] Memcached commands supported

The memcached storage commands set, add, replace, prepend, and append uses the $memc_key as the key, $memc_exptime as the expiration time (or delay) (defaults to 0), $memc_flags as the flags (defaults to 0), to build the corresponding memcached queries.

If $memc_value is not defined at all, then the request body will be used as the value of the $memc_value except for the incr and decr commands. Note that if $memc_value is defined as an empty string (""), that empty string will still be used as the value as is.

The following memcached commands have been implemented and tested (with their parameters marked by corresponding nginx variables defined by this module):

[edit] get $memc_key

Retrieves the value using a key. 

  location /foo {
      set $memc_cmd 'get';
      set $memc_key 'my_key';
 
      memc_pass 127.0.0.1:11211;
 
      add_header X-Memc-Flags $memc_flags;
  }

Returns 200 OK with the value put into the response body if the key is found, or 404 Not Found otherwise. The flags number will be set into the $memc_flags variable so it's often desired to put that info into the response headers by means of the standard add_header directive.

It returns 502 for ERROR, CLIENT_ERROR, or SERVER_ERROR.

[edit] set $memc_key $memc_flags $memc_exptime $memc_value

To use the request body as the memcached value, just avoid setting the $memc_value variable: 

  # POST /foo
  # my value...
  location /foo {
      set $memc_cmd 'set';
      set $memc_key 'my_key';
      set $memc_flags 12345;
      set $memc_exptime 24;
 
      memc_pass 127.0.0.1:11211;
  }

Or let the $memc_value hold the value: 

  location /foo {
      set $memc_cmd 'set';
      set $memc_key 'my_key';
      set $memc_flags 12345;
      set $memc_exptime 24;
      set $memc_value 'my_value';
 
      memc_pass 127.0.0.1:11211;
  }

Returns 201 Created if the upstream memcached server replies STORED, 200 for NOT_STORED, 404 for NOT_FOUND, 502 for ERROR, CLIENT_ERROR, or SERVER_ERROR.

The original memcached responses are returned as the response body except for 404 NOT FOUND.

[edit] add $memc_key $memc_flags $memc_exptime $memc_value

Similar to the set command.

[edit] replace $memc_key $memc_flags $memc_exptime $memc_value

Similar to the set command.

[edit] append $memc_key $memc_flags $memc_exptime $memc_value

Similar to the set command.

Note that at least memcached version 1.2.2 does not support the "append" and "prepend" commands. At least 1.2.4 and later versions seem to supports these two commands.

[edit] prepend $memc_key $memc_flags $memc_exptime $memc_value

Similar to the append command.

[edit] delete $memc_key

Deletes the memcached entry using a key. 

  location /foo
      set $memc_cmd delete;
      set $memc_key my_key;
 
      memc_pass 127.0.0.1:11211;
  }

Returns 200 OK if deleted successfully, 404 Not Found for NOT_FOUND, or 502 for ERROR, CLIENT_ERROR, or SERVER_ERROR.

The original memcached responses are returned as the response body except for 404 NOT FOUND.

[edit] delete $memc_key $memc_exptime

Similar to the delete $memc_key command except it accepts an optional expiration time specified by the $memc_exptime variable.

This command is no longer available in the latest memcached version 1.4.4.

[edit] incr $memc_key $memc_value

Increments the existing value of $memc_key by the amount specified by $memc_value: 

  location /foo {
      set $memc_key my_key;
      set $memc_value 2;
      memc_pass 127.0.0.1:11211;
  }

In the preceding example, every time we access /foo will cause the value of my_key increments by 2.

Returns 200 OK with the new value associated with that key as the response body if successful, or 404 Not Found if the key is not found.

It returns 502 for ERROR, CLIENT_ERROR, or SERVER_ERROR.

[edit] decr $memc_key $memc_value

Similar to incr $memc_key $memc_value.

[edit] flush_all

Mark all the keys on the memcached server as expired: 

  location /foo {
      set $memc_cmd flush_all;
      memc_pass 127.0.0.1:11211;
  }

[edit] flush_all $memc_exptime

Just like flush_all but also accepts an expiration time specified by the $memc_exptime variable.

[edit] stats

Causes the memcached server to output general-purpose statistics and settings 

  location /foo {
      set $memc_cmd stats;
      memc_pass 127.0.0.1:11211;
  }

Returns 200 OK if the request succeeds, or 502 for ERROR, CLIENT_ERROR, or SERVER_ERROR.

The raw stats command output from the upstream memcached server will be put into the response body.

[edit] version

Queries the memcached server's version number: 

  location /foo {
      set $memc_cmd version;
      memc_pass 127.0.0.1:11211;
  }

Returns 200 OK if the request succeeds, or 502 for ERROR, CLIENT_ERROR, or SERVER_ERROR.

The raw version command output from the upstream memcached server will be put into the response body.

[edit] Directives

All the standard memcached module directives in nginx 0.8.28 are directly inherited, with the memcached_ prefixes replaced by memc_. For example, the memcached_pass directive is spelled memc_pass.

Here we only document the most important two directives (the latter is a new directive introduced by this module).

[edit] memc_pass

syntax: memc_pass <memcached server IP address>:<memcached server port>

syntax: memc_pass <memcached server hostname>:<memcached server port>

syntax: memc_pass <upstream_backend_name>

syntax: memc_pass unix:<path_to_unix_domain_socket>

default: none

context: http, server, location, if

phase: content

Specify the memcached server backend.

[edit] memc_cmds_allowed

syntax: memc_cmds_allowed <cmd>...

default: none

context: http, server, location, if

Lists memcached commands that are allowed to access. By default, all the memcached commands supported by this module are accessible. An example is 

   location /foo {
       set $memc_cmd $arg_cmd;
       set $memc_key $arg_key;
       set $memc_value $arg_val;
 
       memc_pass 127.0.0.1:11211;
 
       memc_cmds_allowed get;
   }

[edit] memc_flags_to_last_modified

syntax: memc_flags_to_last_modified on|off

default: off

context: http, server, location, if

Read the memcached flags as epoch seconds and set it as the value of the Last-Modified header. For conditional GET, it will signal nginx to return 304 Not Modified response to save bandwidth.

[edit] memc_connect_timeout

syntax: memc_connect_timeout <time>

default: 60s

context: http, server, location

The timeout for connecting to the memcached server, in seconds by default.

It's wise to always explicitly specify the time unit to avoid confusion. Time units supported are "s"(seconds), "ms"(milliseconds), "y"(years), "M"(months), "w"(weeks), "d"(days), "h"(hours), and "m"(minutes).

This time must be less than 597 hours.

[edit] memc_send_timeout

syntax: memc_send_timeout <time>

default: 60s

context: http, server, location

The timeout for sending TCP requests to the memcached server, in seconds by default.

It's wise to always explicitly specify the time unit to avoid confusion. Time units supported are "s"(seconds), "ms"(milliseconds), "y"(years), "M"(months), "w"(weeks), "d"(days), "h"(hours), and "m"(minutes).

This time must be less than 597 hours.

[edit] memc_read_timeout

syntax: memc_read_timeout <time>

default: 60s

context: http, server, location

The timeout for reading TCP responses from the memcached server, in seconds by default.

It's wise to always explicitly specify the time unit to avoid confusion. Time units supported are "s"(seconds), "ms"(milliseconds), "y"(years), "M"(months), "w"(weeks), "d"(days), "h"(hours), and "m"(minutes).

This time must be less than 597 hours.

[edit] memc_buffer_size

syntax: memc_buffer_size <size>

default: 4k/8k

context: http, server, location

This buffer size is used for the memory buffer to hold

  • the complete response for memcached commands other than get,
  • the complete response header (i.e., the first line of the response) for the get memcached command.

This default size is the page size, may be 4k or 8k.

[edit] Installation

You're recommended to install this module (as well as the Nginx core and many other goodies) via the ngx_openresty bundle. See the installation steps for ngx_openresty.

Alternatively, you can compile this module into the standard Nginx source distribution by hand:

Grab the nginx source code from nginx.org, for example, the version 1.2.1 (see nginx compatibility), and then build the source with this module: 

    wget 'http://nginx.org/download/nginx-1.2.1.tar.gz'
    tar -xzvf nginx-1.2.1.tar.gz
    cd nginx-1.2.1/
 
    # Here we assume you would install you nginx under /opt/nginx/.
    ./configure --prefix=/opt/nginx \
        --add-module=/path/to/memc-nginx-module
 
    make -j2
    make install

Download the latest version of the release tarball of this module from memc-nginx-module file list.

[edit] For Developers

The memached response parsers were generated by Ragel. If you want to regenerate the parser's C file, i.e., src/ngx_http_memc_response.c, use the following command from the root of the memc module's source tree: 

    $ ragel -G2 src/ngx_http_memc_response.rl

[edit] Compatibility

The following versions of Nginx should work with this module:

  • 1.2.x (last tested: 1.2.1)
  • 1.1.x (last tested: 1.1.5)
  • 1.0.x (last tested: 1.0.10)
  • 0.9.x (last tested: 0.9.4)
  • 0.8.x (last tested: 0.8.54)
  • 0.7.x >= 0.7.46 (last tested: 0.7.68)

It's worth mentioning that some 0.7.x versions older than 0.7.46 might also work, but I can't easily test them because the test suite makes extensive use of the echo module's echo_location directive, which requires at least nginx 0.7.46 :)

Earlier versions of Nginx like 0.6.x and 0.5.x will not work.

If you find that any particular version of Nginx above 0.7.46 does not work with this module, please consider reporting a bug.

[edit] Report Bugs

Although a lot of effort has been put into testing and code tuning, there must be some serious bugs lurking somewhere in this module. So whenever you are bitten by any quirks, please don't hesitate to

  1. create a ticket on the issue tracking interface provided by GitHub,
  2. or send a bug report or even patches to the nginx mailing list.

[edit] Source Repository

Available on github at agentzh/memc-nginx-module.

[edit] ChangeLog

[edit] v0.12

  • fixed the spots that trigger the unused-but-set-variable warning by gcc 4.6.
  • added more debug information when memcached sends back "invalid" responses.
  • we now document the timeout units properly. it should default to seconds.
  • now we use the 2-clause bsd license.
  • added an error message when no upstream backend is found in "memc_pass $backend".

[edit] v0.11

  • fixed the zero size buf alert in error.log when $memc_value is set to empty (""). thanks iframist.

[edit] v0.10

  • we no longer use the problematic ngx_strXcmp macros in our source because it may cause invalid reads and thus segmentation faults. thanks Piotr Sikora.

[edit] v0.09

  • now we copy out r->request_body->bufs for our memcached request to avoid modifying the original request body. Thanks Matthieu Tourne.

[edit] v0.08

  • now the memc commands other than get work with subrequests in memory. Thanks Yao Xinming for reporting it. Using storage memcached commands in ngx_eval module's eval blocks no longer hang the server.

[edit] v0.07

  • applied the patch from nginx 0.8.35 that fixed a bug that ngx_eval may issue the incorrect error message "memcached sent invalid trailer".

[edit] v0.06

[edit] v0.05

  • removed the memc_bind directive since it won't compile with nginx 0.8.31.

[edit] v0.04

  • to ensure Maxim's ngx_http_upstream_keepalive module caches our connections even if u->headers_in->status is 201 (Created).
  • updated docs to make it clear that this module can work with "upstream" multi-server backends. thanks Bernd Dorn for reporting it.

[edit] v0.03

  • fixed a connection leak caused by an extra r->main->count++ operation: we should NOT do r->main->count++ after calling the ngx_http_read_client_request_body function in our content handler.

[edit] v0.02

  • applied the (minor) optimization trick suggested by Marcus Clyne: creating our variables and save their indexes at post-config phase when the memc_pass directive is actually used in the config file.

[edit] v0.01

  • initial release.

[edit] Test Suite

This module comes with a Perl-driven test suite. The test cases are declarative too. Thanks to the Test::Base module in the Perl world.

To run it on your side: 

    $ PATH=/path/to/your/nginx-with-memc-module:$PATH prove -r t

You need to terminate any Nginx processes before running the test suite if you have changed the Nginx server binary.

Either LWP::UserAgent or IO::Socket is used by the test scaffold.

Because a single nginx server (by default, localhost:1984) is used across all the test scripts (.t files), it's meaningless to run the test suite in parallel by specifying -jN when invoking the prove utility.

You should also keep a memcached server listening on the 11211 port at localhost before running the test suite.

Some parts of the test suite requires modules rewrite and echo to be enabled as well when building Nginx.

[edit] TODO

  • add support for the memcached commands cas, gets and stats $memc_value.
  • add support for the noreply option.

[edit] Getting involved

You'll be very welcomed to submit patches to the author or just ask for a commit bit to the source repository on GitHub.

[edit] Author

agentzh (章亦春) <agentzh@gmail.com>

This wiki page is also maintained by the author himself, and everybody is encouraged to improve this page as well.

[edit] Copyright & License

The code base is borrowed directly from the standard memcached module in the Nginx 0.8.28 core. This part of code is copyrighted by Igor Sysoev.

Copyright (c) 2009, 2010, 2011, Zhang "agentzh" Yichun (章亦春) <agentzh@gmail.com>.

This module is licensed under the terms of the BSD license.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

  • Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
  • Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

[edit] See Also

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