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ngx_http_upstream_hash_module
-This module is not distributed with the Nginx source. Installation instructions are below.
The upstream_hash module provides simple upstream load distribution by hashing a configurable variable (e.g., the request URI, incoming HTTP headers, or some combination). Example usage:
upstream backend {
- server server1;
- server server2;
- hash $request_uri;
-}
-Here, Nginx will choose server1 or server2 by hashing the request URI ($request_uri).
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Directives
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hash
-syntax hash $variable
context upstream
Enables upstream hashing of $variable.
When present, the "server" directives cannot take any arguments ("weight", "max_fails", etc.).
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hash_again
-syntax hash_again number
default 0
context upstream
Number of times to rehash the value and choose a different server if the backend connection fails. Increase this number to provide high availability.
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Installation
-This module is not distributed with the Nginx source. You can download the request_hash module here: nginx_upstream_hash-0.3.tar.gz
After extracting, you will need to patch the latest Nginx source (0.7.11 as of this writing). Run patch like this:
cd nginx-0.7.11 - patch -p0 < /path/to/upstream/hash/directory/nginx.patch -
Then add the following option to your Nginx ./configure command:
--add-module=path/to/upstream/hash/directory -
Then "make" and "make install" as usual.
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The hash algorithm
-As of 0.3, the hash algorithm and the failover algorithm use a CRC-32 computation compatible with PECL Memcache.
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Changes
-- * 0.3: Feature: PECL Memcache compatibility. Change: Removed "hash_method" directive.
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Bugs
-Send bug reports to Evan Miller.