ngx_http_upstream_memcached_hash_module

Skip to the end for download. Git repository: git clone git://openhack.ru/nginx-patched.git branch memcached_hash.

---

syntax: memcached_hash [ketama_points=points] [weight_scale=weight] default: none context: upstream

syntax: set $memcached_namespace "string"; default: "" context: server, location, if

This module implements memcached_hash directive for upstream blocks. The purpose of this directive is to direct nginx to the right memcached server, the one that would be used by  Cache::Memcached::Fast (or its ancestor  Cache::Memcached) for the same key. Thus you may upload the data to memcached cluster with the Perl script using C::M::F (or in general with any client that is compatible with C::M), and then serve that data with nginx.

Parameters of memcached_hash directive:

ketama_points=points - how many points the server has

weight_scale=scale - denominator by which ketama points and server weights are scaled down. Thus, if you have ketama_points=150 and weight_scale=10 the server gets 150/10 = 15 points.

The typical configuration will be

server {
    location / {
        set             $memcached_key   "$uri$is_args$args";
        set             $memcached_namespace   "prefix";
        memcached_pass  memcached_cluster;
        error_page      404 502 504 = @fallback;
    }

    location @fallback {
        proxy_pass      http://backend;
    }
}

and memcached_cluster will be defined as

upstream memcached_cluster {
    memcached_hash;

    server localhost:11211 weight=2;
    server 192.168.254.2:11211;
    server unix:/path/to/unix.sock weight=4;
}

or

upstream memcached_cluster {
    memcached_hash ketama_points=150 weight_scale=10;

    server localhost:11211 weight=25;
    server 192.168.254.2:11211 weight=10;
    server unix:/path/to/unix.sock weight=40;
}

when corresponding parameters to Cache::Memcached::Fast are

my $memd = new Cache::Memcached::Fast({
    servers => [ { address => 'localhost:11211', weight => 2 },
                 '192.168.254.2:11211',
                 { address => '/path/to/unix.sock', weight => 4 } ],
    namespace => 'prefix',
    ...
});

or

my $memd = new Cache::Memcached::Fast({
    servers => [ { address => 'localhost:11211', weight => 2.5 },
                 '192.168.254.2:11211',
                 { address => '/path/to/unix.sock', weight => 4 } ],
    namespace => 'prefix',
    ketama_points => 150,
    ...
});

respectively. See  README for further details.

Back to nginx-patched.